dextromethorphan/quinidine (Rx)

Brand and Other Names:Nuedexta
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Dosing & Uses

AdultPediatricGeriatric

Dosing Forms & Strengths

dextromethorphan/quinidine

capsule

  • 20mg/10mg

Pseudobulbar Affect

Indicated for PBA and symptoms associated with a variety of neurological conditions (eg, MS, ALS) that result in involuntary, sudden, and frequent episodes of laughing and/or crying

PBA occurs secondary to a variety of otherwise unrelated neurologic conditions, and is characterized by involuntary, sudden, and frequent episodes of laughing and/or crying; episodes typically occur out of proportion or incongruent to the underlying emotional state

PBA is a specific condition, distinct from other types of emotional lability that may occur in patients with neurological disease or injury

1 capsule PO qDay for 7days, THEN 1 capsule q12h

Dosage Modifications

Renal impairment

  • Mild or moderate: No dose adjustment required
  • Severe: Safety and effaicacy not established

Hepatic impairment

  • Mild or moderate: No dosage adjustment required; increase in adverse reactions possible with moderate impairment
  • Severe: Safety and efficacy not established

Amyotrophic Lateral Sclerosis (Orphan)

Orphan designation for treatment of amyotrophic lateral sclerosis (ALS)

Sponsor

  • Avanir Pharmaceuticals; 30 Enterprise, Suite 400; Aliso Viejo, California 92656

Safety and efficacy not established

Dose selection for elderly should be cautious, usually starting at low end of dosing range, reflecting greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy

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Interactions

Interaction Checker

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            Contraindicated (72)

            • amitriptyline

              quinidine and amitriptyline both increase QTc interval. Contraindicated.

            • amoxapine

              quinidine and amoxapine both increase QTc interval. Contraindicated.

            • artemether/lumefantrine

              quinidine and artemether/lumefantrine both increase QTc interval. Contraindicated.

            • chloroquine

              quinidine will increase the level or effect of chloroquine by Other (see comment). Contraindicated. Quinidine is contraindicated in patients receiving drugs that both prolong the QT interval and are metabolized by CYP2D6, such as chloroquine

            • chlorpromazine

              chlorpromazine and quinidine both increase QTc interval. Contraindicated.

            • clarithromycin

              quinidine and clarithromycin both increase QTc interval. Contraindicated.

            • clomipramine

              quinidine and clomipramine both increase QTc interval. Contraindicated.

            • cobimetinib

              quinidine will increase the level or effect of cobimetinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Avoid coadministration with strong CYP3A4 inhibitors with (increases cobimetinib systemic exposure by 6.7-fold).

            • conivaptan

              quinidine will increase the level or effect of conivaptan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of conivaptan with strong CYP3A4 inhibitors is contraindicated.

            • desipramine

              quinidine and desipramine both increase QTc interval. Contraindicated.

            • dihydroergotamine

              quinidine increases levels of dihydroergotamine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

            • dihydroergotamine intranasal

              quinidine increases levels of dihydroergotamine intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

            • disopyramide

              quinidine and disopyramide both increase QTc interval. Contraindicated.

            • dofetilide

              quinidine and dofetilide both increase QTc interval. Contraindicated.

              quinidine, dofetilide. Either increases effects of the other by pharmacodynamic synergism. Contraindicated. Additive cardiac effects.

            • dosulepin

              quinidine and dosulepin both increase QTc interval. Contraindicated.

            • doxepin

              quinidine and doxepin both increase QTc interval. Contraindicated.

            • dronedarone

              quinidine and dronedarone both increase QTc interval. Contraindicated.

            • droperidol

              quinidine and droperidol both increase QTc interval. Contraindicated.

            • eliglustat

              quinidine will increase the level or effect of eliglustat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors are contraindicated with eliglustat poor or intermediate metabolizers; reduce eliglustat dose from 84 mg BID to 84 mg once daily in extensive metabolizers; eliglustat is contraindiated if strong or moderate CYP2D6 inhibitors are given concomitantly with strong or moderate CYP3A inhibitors

              quinidine increases levels of eliglustat by affecting hepatic enzyme CYP2D6 metabolism. Contraindicated. If coadministered with strong or moderate CYP2D6 inhibitors, reduce eliglustat dose from 84 mg BID to 84 mg once daily in extensive and intermediate metabolizers; eliglustat is contraindiated if strong or moderate CYP2D6 inhibitors are given concomitantly with strong or moderate CYP3A inhibitors.

            • epinephrine

              epinephrine and quinidine both increase QTc interval. Contraindicated.

            • epinephrine racemic

              epinephrine racemic and quinidine both increase QTc interval. Contraindicated.

            • erythromycin base

              quinidine and erythromycin base both increase QTc interval. Contraindicated.

            • erythromycin ethylsuccinate

              quinidine and erythromycin ethylsuccinate both increase QTc interval. Contraindicated.

            • erythromycin lactobionate

              quinidine and erythromycin lactobionate both increase QTc interval. Contraindicated.

            • erythromycin stearate

              quinidine and erythromycin stearate both increase QTc interval. Contraindicated.

            • fingolimod

              fingolimod increases effects of quinidine by pharmacodynamic synergism. Contraindicated. Due to increased risk of bradycardia, AV block, and torsade de pointes, concomitant use is contraindicated.

            • flibanserin

              quinidine will increase the level or effect of flibanserin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of flibanserin with moderate or strong CYP3A4 inhibitors is contraindicated. Severe hypotension or syncope can occur.

            • fluconazole

              fluconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

              quinidine and fluconazole both increase QTc interval. Contraindicated.

            • fluphenazine

              fluphenazine and quinidine both increase QTc interval. Contraindicated.

            • goserelin

              goserelin increases toxicity of quinidine by QTc interval. Contraindicated. Increases risk of torsades de pointes.

            • haloperidol

              quinidine and haloperidol both increase QTc interval. Contraindicated.

            • ibutilide

              quinidine and ibutilide both increase QTc interval. Contraindicated.

            • imipramine

              quinidine and imipramine both increase QTc interval. Contraindicated.

            • indapamide

              quinidine and indapamide both increase QTc interval. Contraindicated.

            • isocarboxazid

              isocarboxazid and dextromethorphan both increase serotonin levels. Contraindicated.

            • itraconazole

              itraconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Both drugs will increase QT interval. Coadministration of quinidine and itraconazole is contraindicated during and 2 weeks after itraconazole treatment.

              quinidine will increase the level or effect of itraconazole by P-glycoprotein (MDR1) efflux transporter. Contraindicated. Both drugs will increase QT interval

              quinidine and itraconazole both increase QTc interval. Contraindicated.

            • ivabradine

              quinidine will increase the level or effect of ivabradine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of ivabradine with strong CYP3A4 inhibitors is contraindicated.

            • ketoconazole

              quinidine and ketoconazole both increase QTc interval. Contraindicated.

            • lefamulin

              lefamulin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Lefamulin is contraindicated with CYP3A substrates know to prolong the QT interval.

            • leuprolide

              leuprolide increases toxicity of quinidine by QTc interval. Contraindicated. Increases risk of torsades de pointes.

            • lofepramine

              quinidine and lofepramine both increase QTc interval. Contraindicated.

            • lomitapide

              quinidine increases levels of lomitapide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Increases lomitapide levels several folds.

            • lovastatin

              quinidine will increase the level or effect of lovastatin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors increase systemic statin exposure and risk of myopathy, including rhabdomyolysis

            • lumefantrine

              quinidine and lumefantrine both increase QTc interval. Contraindicated.

            • maprotiline

              quinidine and maprotiline both increase QTc interval. Contraindicated.

            • mifepristone

              mifepristone increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Contraindicated with CYP3A substrates that have a narrow therapeutic index; combination may prolong QT interval .

            • moxifloxacin

              quinidine and moxifloxacin both increase QTc interval. Contraindicated.

            • naloxegol

              quinidine will increase the level or effect of naloxegol by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Coadministration of naloxegol with strong CYP3A4 inhibitors can significantly increase naloxegol systemic exposure which may precipitate opioid withdrawal symptoms

            • nilotinib

              quinidine and nilotinib both increase QTc interval. Contraindicated.

            • nortriptyline

              quinidine and nortriptyline both increase QTc interval. Contraindicated.

            • octreotide

              quinidine and octreotide both increase QTc interval. Contraindicated.

            • octreotide (Antidote)

              quinidine and octreotide (Antidote) both increase QTc interval. Contraindicated.

            • pentamidine

              quinidine and pentamidine both increase QTc interval. Contraindicated.

            • perphenazine

              perphenazine and quinidine both increase QTc interval. Contraindicated.

            • phenelzine

              phenelzine and dextromethorphan both increase serotonin levels. Contraindicated.

            • pimozide

              quinidine and pimozide both increase QTc interval. Contraindicated.

            • procainamide

              quinidine and procainamide both increase QTc interval. Contraindicated.

            • procarbazine

              procarbazine and dextromethorphan both increase serotonin levels. Contraindicated. Combination is contraindicated within 2 weeks of MAOI use.

            • prochlorperazine

              prochlorperazine and quinidine both increase QTc interval. Contraindicated.

            • promazine

              promazine and quinidine both increase QTc interval. Contraindicated.

            • promethazine

              promethazine and quinidine both increase QTc interval. Contraindicated.

            • protriptyline

              quinidine and protriptyline both increase QTc interval. Contraindicated.

            • rasagiline

              rasagiline and dextromethorphan both increase serotonin levels. Contraindicated. Risk of psychosis episodes or bizarre behavior.

            • regorafenib

              quinidine, regorafenib. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Strong CYP3A4 inhibitors increase regorafenib levels and decrease exposure of the active metabolites M-2 and M-5.

            • safinamide

              dextromethorphan, safinamide. Other (see comment). Contraindicated. Comment: Coadministration of MAOIs and dextromethorphan has been reported to cause episodes of psychosis or bizarre behavior.

            • saquinavir

              saquinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

            • selegiline

              selegiline and dextromethorphan both increase serotonin levels. Contraindicated.

            • sotalol

              quinidine and sotalol both increase QTc interval. Contraindicated.

            • thioridazine

              thioridazine and quinidine both increase QTc interval. Contraindicated.

            • tipranavir

              tipranavir increases levels of quinidine by decreasing metabolism. Contraindicated.

              tipranavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated.

            • tranylcypromine

              tranylcypromine and dextromethorphan both increase serotonin levels. Contraindicated.

            • trazodone

              quinidine and trazodone both increase QTc interval. Contraindicated.

            Serious - Use Alternative (224)

            • abametapir

              abametapir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. For 2 weeks after abametapir application, avoid taking drugs that are CYP3A4 substrates. If not feasible, avoid use of abametapir.

            • ado-trastuzumab emtansine

              quinidine increases levels of ado-trastuzumab emtansine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. DM1, the cytotoxic component, is metabolized mainly by CYP3A4; strong CYP3A4 inhibitors may increase DM1 exposure and toxicity.

            • afatinib

              quinidine increases levels of afatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Reduce afatinib daily dose by 10 mg if not tolerated when coadministered with P-gp inhibitors.

            • alfuzosin

              alfuzosin and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • amikacin

              quinidine will increase the level or effect of amikacin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • amiodarone

              quinidine will increase the level or effect of amiodarone by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

              quinidine and amiodarone both increase QTc interval. Avoid or Use Alternate Drug.

            • amitriptyline

              amitriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

              quinidine will increase the level or effect of amitriptyline by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • amoxapine

              amoxapine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • apalutamide

              apalutamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of apalutamide, a strong CYP3A4 inducer, with drugs that are CYP3A4 substrates can result in lower exposure to these medications. Avoid or substitute another drug for these medications when possible. Evaluate for loss of therapeutic effect if medication must be coadministered. Adjust dose according to prescribing information if needed.

            • apixaban

              quinidine will increase the level or effect of apixaban by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If taking apixaban dose >2.5 mg BID, decrease dose by 50% if coadministered with strong dual inhibitors of CYP3A4 and P-gp; if currently taking apixaban 2.5 mg PO BID, avoid coadministration with strong dual inhibitors of CYP3A4 and P-gp

            • apomorphine

              apomorphine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • aripiprazole

              aripiprazole and quinidine both increase QTc interval. Contraindicated.

            • arsenic trioxide

              quinidine and arsenic trioxide both increase QTc interval. Avoid or Use Alternate Drug.

            • atomoxetine

              atomoxetine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • atorvastatin

              quinidine will increase the level or effect of atorvastatin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • axitinib

              quinidine increases levels of axitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If unable to avoid coadministration with strong CYP3A4 inhibitors, reduce axitinib dose by 50%.

            • bazedoxifene/conjugated estrogens

              quinidine will increase the level or effect of bazedoxifene/conjugated estrogens by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • bedaquiline

              quinidine will increase the level or effect of bedaquiline by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of bedaquiline with strong CYP3A4 inhibitors for >14 consecutive days, unless the benefit of treatment outweighs the risk

            • bosutinib

              quinidine increases levels of bosutinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Strong CYP3A4 inhibitors increases bosutinib plasma concentration ~5-fold.

              quinidine increases levels of bosutinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • bremelanotide

              bremelanotide will decrease the level or effect of quinidine by Other (see comment). Avoid or Use Alternate Drug. Bremelanotide may slow gastric emptying and potentially reduces the rate and extent of absorption of concomitantly administered oral medications. Avoid use when taking any oral drug that is dependent on threshold concentrations for efficacy. Interactions listed are representative examples and do not include all possible clinical examples.

            • brigatinib

              brigatinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Brigatinib induces CYP3A4 in vitro. Coadministration with CYP3A4 substrates, particularly those with a narrow therapeutic index, can result in decreased concentrations and loss of efficacy. If unable to avoid coadministration, monitor CYP3A4 substrate levels and adjust dose as needed.

            • budesonide

              quinidine will increase the level or effect of budesonide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • buspirone

              buspirone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • cabozantinib

              quinidine will increase the level or effect of cabozantinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of cabozantinib with strong CYP3A4 inhibitors. If a strong CYP3A4 inhibitor is required, decrease cabozantinib dose by 40 mg/day (Cometriq) or by 20 mg/day (Cabometyx). Resume previous dose 2-3 days after strong CYP3A4 inhibitor discontinued.

            • carbamazepine

              carbamazepine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • carvedilol

              quinidine will increase the level or effect of carvedilol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • ceritinib

              quinidine increases levels of ceritinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid if possible; if concomitant use is unavoidable, reduce ceritinib dose by ~33%; after discontinuation of strong CYP3A inhibitor, resume at previous dose.

              ceritinib increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concurrent use of CYP3A substrates known to have narrow therapeutic indices or substrates primarily metabolized by CYP3A during treatment with ceritinib; if use of these medications is unavoidable, consider dose.

              ceritinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • chloroquine

              chloroquine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.

            • chlorpromazine

              quinidine, chlorpromazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • cimetidine

              cimetidine will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

              quinidine will increase the level or effect of cimetidine by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

            • citalopram

              citalopram and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Combination may increase risk of serotonin syndrome or neuroleptic malignant syndrome-like reactions.

            • clarithromycin

              clarithromycin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • clobetasone

              quinidine will increase the level or effect of clobetasone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • clomipramine

              clomipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

              quinidine will increase the level or effect of clomipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • clozapine

              clozapine and quinidine both increase QTc interval. Contraindicated.

            • desipramine

              desipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • colchicine

              quinidine will increase the level or effect of colchicine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Avoid use of colchicine with P-gp inhibitors. If coadministration is necessary, decrease colchicine dose or frequency as recommended in prescribing information. Use of any colchicine product in conjunction with P-gp inhibitors is contraindicated in patients with renal or hepatic impairment.

            • conjugated estrogens

              quinidine will increase the level or effect of conjugated estrogens by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • conjugated estrogens, vaginal

              quinidine will increase the level or effect of conjugated estrogens, vaginal by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • cortisone

              quinidine will increase the level or effect of cortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • crizotinib

              crizotinib increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of crizotinib with CYP3A substrates with narrow therapeutic indices should be avoided. ECG monitoring is recommended, along with drugs that may prolong the QT interval.

              crizotinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • dabrafenib

              quinidine increases levels of dabrafenib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • dapsone topical

              quinidine, dapsone topical. unspecified interaction mechanism. Avoid or Use Alternate Drug. Avoid coadministration of dapsone topical with oral dapsone or antimalarial medications because of the potential for hemolytic reactions.

            • dasatinib

              quinidine and dasatinib both increase QTc interval. Avoid or Use Alternate Drug.

            • deflazacort

              quinidine will increase the level or effect of deflazacort by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • desipramine

              quinidine will increase the level or effect of desipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • desvenlafaxine

              dextromethorphan and desvenlafaxine both increase serotonin levels. Avoid or Use Alternate Drug.

            • dexamethasone

              quinidine will increase the level or effect of dexamethasone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • digoxin

              quinidine will increase the level or effect of digoxin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              quinidine will increase the level or effect of digoxin by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

            • diphenhydramine

              quinidine, diphenhydramine. Mechanism: pharmacodynamic synergism. Contraindicated. Risk of prolonged QTc interval.

            • docetaxel

              quinidine will increase the level or effect of docetaxel by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • dofetilide

              quinidine will increase the level or effect of dofetilide by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

              dofetilide increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.

            • dolasetron

              quinidine and dolasetron both increase QTc interval. Avoid or Use Alternate Drug.

            • doxepin

              quinidine will increase the level or effect of doxepin by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Both agents increase QTc interval.

              doxepin and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • duloxetine

              duloxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

              quinidine will increase the level or effect of duloxetine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              duloxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • edoxaban

              quinidine will increase the level or effect of edoxaban by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Dose adjustment may be required with strong P-gp inhibitors. DVT/PE treatment: Decrease dose to 30 mg PO once daily. NVAF: No dose reduction recommended

            • escitalopram

              escitalopram and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • encorafenib

              encorafenib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Encorafenib is associated with dose-dependent QTc interval prolongation. Avoid with drugs known to prolong QT interval.

            • entrectinib

              quinidine and entrectinib both increase QTc interval. Avoid or Use Alternate Drug.

            • erdafitinib

              erdafitinib, quinidine. Other (see comment). Avoid or Use Alternate Drug. Comment: Avoid coadministration during initial dosing adjustment period (ie, first 21 days). Increases in serum phosphate levels are a pharmacodynamic effect of FGFR inhibition. Serum phosphate binders may obscure decisions regarding initial dosage increase.

              erdafitinib, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration with erdafitinib and sensitive CYP3A4 substrates with narrow therapeutic indices. Erdafitinib may altered plasma concentrations of CYP3A4 substrates, leading to either loss of activity or increased toxicity of the substrate.

              erdafitinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If coadministration unavoidable, separate administration by at least 6 hr before or after administration of P-gp substrates with narrow therapeutic index.

            • eribulin

              eribulin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Potential for enhanced QTc-prolonging effects; if concurrent use is necessary then ECG monitoring is recommended.

            • erlotinib

              quinidine will increase the level or effect of erlotinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • erythromycin base

              erythromycin base will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • erythromycin ethylsuccinate

              erythromycin ethylsuccinate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • erythromycin lactobionate

              erythromycin lactobionate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • erythromycin stearate

              erythromycin stearate will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • escitalopram

              escitalopram increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug.

            • estradiol

              quinidine will increase the level or effect of estradiol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • estrogens conjugated synthetic

              quinidine will increase the level or effect of estrogens conjugated synthetic by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • estropipate

              quinidine will increase the level or effect of estropipate by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • ethinylestradiol

              quinidine will increase the level or effect of ethinylestradiol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • everolimus

              quinidine will increase the level or effect of everolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • fentanyl

              quinidine will increase the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

            • fentanyl intranasal

              quinidine will increase the level or effect of fentanyl intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

            • fentanyl transdermal

              quinidine will increase the level or effect of fentanyl transdermal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

            • fentanyl transmucosal

              quinidine will increase the level or effect of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of CYP3A4 inhibitors with fentanyl is necessary, monitor patients for respiratory depression and sedation at frequent intervals and consider fentanyl dose adjustments until stable drug effects are achieved.

            • fexinidazole

              fexinidazole and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Avoid coadministration of fexinidazole with drugs known to block potassium channels and/or prolong QT interval.

              fexinidazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Fexinidazole inhibits CYP3A4. Coadministration may increase risk for adverse effects of CYP3A4 substrates.

            • flecainide

              quinidine will increase the level or effect of flecainide by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              quinidine and flecainide both increase QTc interval. Avoid or Use Alternate Drug.

            • fludrocortisone

              quinidine will increase the level or effect of fludrocortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • fluoxetine

              fluoxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

              quinidine will increase the level or effect of fluoxetine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              fluoxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              quinidine and fluoxetine both increase QTc interval. Avoid or Use Alternate Drug.

            • fluphenazine

              quinidine, fluphenazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • fluvoxamine

              fluvoxamine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • fluticasone intranasal

              quinidine will increase the level or effect of fluticasone intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Strong CYP3A4 inhibitors may increase systemic corticosteroid adverse effects; monitor for signs/symptoms of high corticosteroid concentrations including Cushing type signs/symptoms.

            • fluvoxamine

              fluvoxamine and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • formoterol

              quinidine and formoterol both increase QTc interval. Avoid or Use Alternate Drug.

            • fosamprenavir

              fosamprenavir increases levels of quinidine by unspecified interaction mechanism. Avoid or Use Alternate Drug.

            • foscarnet

              quinidine and foscarnet both increase QTc interval. Avoid or Use Alternate Drug.

            • gentamicin

              quinidine will increase the level or effect of gentamicin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • glasdegib

              quinidine and glasdegib both increase QTc interval. Avoid or Use Alternate Drug. If coadministration unavoidable, monitor for increased risk of QTc interval prolongation.

            • grapefruit

              grapefruit will increase the level or effect of dextromethorphan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • haloperidol

              quinidine will increase the level or effect of haloperidol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • histrelin

              histrelin increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

            • hydrocortisone

              quinidine will increase the level or effect of hydrocortisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • hydromorphone

              quinidine will increase the level or effect of hydromorphone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • hydroxychloroquine sulfate

              hydroxychloroquine sulfate and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • hydroxyzine

              hydroxyzine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

            • ibrutinib

              quinidine increases levels of ibrutinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concomitant use of ibrutinib and strong CYP3A4 inhibitors. If a strong CYP3A4 inhibitor must be used short-term (eg, anti-infectives for =7 days), interrupt ibrutinib therapy until strong CYP3A4 inhibitor is discontinued.

            • idelalisib

              quinidine will increase the level or effect of idelalisib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministered with strong CYP3A inhibitors, monitor for signs of idelalisib toxicity; follow recommendations for dosage modifications if adverse reactions occur

              idelalisib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Idelalisib is a strong CYP3A inhibitor; avoid coadministration with sensitive CYP3A substrates

            • iloperidone

              quinidine will increase the level or effect of iloperidone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              quinidine and iloperidone both increase QTc interval. Avoid or Use Alternate Drug.

            • imatinib

              quinidine will increase the level or effect of imatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • imipramine

              imipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

              quinidine will increase the level or effect of imipramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • indinavir

              quinidine will increase the level or effect of indinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • levomilnacipran

              levomilnacipran and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • inotuzumab

              inotuzumab and quinidine both increase QTc interval. Avoid or Use Alternate Drug. If unable to avoid concomitant use, obtain ECGs and electrolytes before and after initiation of any drug known to prolong QTc, and periodically monitor as clinically indicated during treatment.

            • ivermectin

              quinidine will increase the level or effect of ivermectin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • ivosidenib

              ivosidenib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Avoid coadministration of QTc prolonging drugs with ivosidenib or replace with alternate therapies. If coadministration of a QTc prolonging drug is unavoidable, monitor for increased risk of QTc interval prolongation.

              ivosidenib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sensitive CYP3A4 substrates with ivosidenib or replace with alternative therapies. If coadministration is unavoidable, monitor patients for loss of therapeutic effect of these drugs.

            • ketoconazole

              ketoconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • lapatinib

              quinidine will increase the level or effect of lapatinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              quinidine and lapatinib both increase QTc interval. Avoid or Use Alternate Drug.

            • lasmiditan

              lasmiditan increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • levofloxacin

              quinidine and levofloxacin both increase QTc interval. Avoid or Use Alternate Drug.

            • linezolid

              linezolid and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Linezolid may increase serotonin as a result of MAO-A inhibition. If linezolid must be administered, discontinue serotonergic drug immediately and monitor for CNS toxicity. Serotonergic therapy may be resumed 24 hours after last linezolid dose or after 2 weeks of monitoring, whichever comes first.

            • lofepramine

              quinidine will increase the level or effect of lofepramine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              lofepramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • lonafarnib

              lonafarnib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration with sensitive CYP3A substrates. If coadministration unavoidable, monitor for adverse reactions and reduce CYP3A substrate dose in accordance with product labeling.

              quinidine will increase the level or effect of lonafarnib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration of lonafarnib (a sensitive CYP3A substrate) with weak CYP3A inhibitors is unavoidable, reduce to, or continue lonafarnib at starting dose. Closely monitor for arrhythmias and events (eg, syncope, heart palpitations) since lonafarnib effect on QT interval is unknown.

            • lorcaserin

              dextromethorphan and lorcaserin both increase serotonin levels. Avoid or Use Alternate Drug.

            • loperamide

              quinidine will increase the level or effect of loperamide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • lopinavir

              lopinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • lorlatinib

              lorlatinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid use of lorlatinib with CYP3A substrates, where minimal concentration changes may lead to serious therapeutic failures of the substrate. If concomitant use is unavoidable, increase CYP3A substrate dosage in accordance with approved product labeling.

            • lovastatin

              quinidine will increase the level or effect of lovastatin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • lumacaftor/ivacaftor

              lumacaftor/ivacaftor will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Lumacaftor is a strong inducer of CYP3A. Avoid coadministration with sensitive CYP3A substrates or CYP3A substrates with a narrow therapeutic index.

            • lurasidone

              lurasidone increases toxicity of quinidine by Other (see comment). Avoid or Use Alternate Drug. Comment: Interaction applies only in setting of acute lurasidone overdose. Lurasidone may enhance QTc prolonging effects of quinidine in overdose setting.

            • macimorelin

              macimorelin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Macimorelin causes an increase of ~11 msec in the corrected QT interval. Avoid coadministration with drugs that prolong QT interval, which could increase risk for developing torsade de pointes-type ventricular tachycardia. Allow sufficient washout time of drugs that are known to prolong the QT interval before administering macimorelin.

            • macitentan

              quinidine will increase the level or effect of macitentan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministering macitentan with strong CYP3A4 inhibitors

            • maprotiline

              maprotiline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • maraviroc

              quinidine will increase the level or effect of maraviroc by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • mefloquine

              quinidine, mefloquine. Mechanism: pharmacodynamic synergism. Contraindicated. Risk of ECG abnormalities, cardiac arrest.

              mefloquine increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Mefloquine may enhance the QTc prolonging effect of high risk QTc prolonging agents.

            • memantine

              memantine, dextromethorphan. Either increases toxicity of the other by pharmacodynamic synergism. Contraindicated.

            • meperidine

              dextromethorphan and meperidine both increase serotonin levels. Avoid or Use Alternate Drug.

            • mestranol

              quinidine will increase the level or effect of mestranol by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • methadone

              quinidine and methadone both increase QTc interval. Avoid or Use Alternate Drug.

            • methamphetamine

              quinidine will increase the level or effect of methamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • methylene blue

              methylene blue and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug. Methylene blue may increase serotonin as a result of MAO-A inhibition. If methylene blue must be administered, discontinue serotonergic drug immediately and monitor for CNS toxicity. Serotonergic therapy may be resumed 24 hours after last methylene blue dose or after 2 weeks of monitoring, whichever comes first.

            • methylprednisolone

              quinidine will increase the level or effect of methylprednisolone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • metoclopramide intranasal

              quinidine will increase the level or effect of metoclopramide intranasal by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Concurrent use of metoclopramide intranasal and strong CYP2D6 inhibitors is not recommended since the metoclopramide intranasal dose cannot be adjusted.

            • metoprolol

              quinidine will increase the level or effect of metoprolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. If concurrent therapy required, monitor cardiac function carefully (blood pressure, heart rate). A dosage adjustment may be required for both drugs.

            • mexiletine

              quinidine will increase the level or effect of mexiletine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • milnacipran

              milnacipran and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • mobocertinib

              mobocertinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If use is unavoidable, increase CYP3A4 substrate dosage in accordance with its prescribing information.

              mobocertinib and quinidine both increase QTc interval. Avoid or Use Alternate Drug. If coadministration unavoidable, reduce mobocertinib dose and monitor QTc interval more frequently.

            • morphine

              quinidine will increase the level or effect of morphine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • nebivolol

              quinidine will increase the level or effect of nebivolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Monitor blood pressure. Reduced doses of nebivolol may be necessary.

            • nefazodone

              nefazodone will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

              nefazodone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • nelfinavir

              quinidine will increase the level or effect of nelfinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              nelfinavir increases levels of quinidine by decreasing metabolism. Contraindicated.

            • nortriptyline

              nortriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • neomycin PO

              quinidine will increase the level or effect of neomycin PO by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • nilotinib

              nilotinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Additive QT prolongation may occur during coadministration of nilotinib and quinidine. Coadministration of nilotinib and a drug that prolongs the QT interval such as dronedarone is not advised

              quinidine will increase the level or effect of nilotinib by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • nortriptyline

              quinidine will increase the level or effect of nortriptyline by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • ofloxacin

              quinidine and ofloxacin both increase QTc interval. Avoid or Use Alternate Drug.

            • olaparib

              quinidine will increase the level or effect of olaparib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If coadministration with strong CYP3A inhibitors cannot be avoided, reduce olaparib dose to 150 mg (capsule) or 100 mg (tablet) PO BID. Do not substitute tablets with capsules.

            • ondansetron

              quinidine and ondansetron both increase QTc interval. Avoid or Use Alternate Drug. Avoid with congenital long QT syndrome; ECG monitoring recommended with concomitant medications that prolong QT interval, electrolyte abnormalities, CHF, or bradyarrhythmias.

            • oxycodone

              quinidine will increase the level or effect of oxycodone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              quinidine increases levels of oxycodone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Oxycodone dose reduction may be warranted when coadministered with strong CYP3A4 inhibitors.

            • oxymorphone

              quinidine will increase the level or effect of oxymorphone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • paclitaxel

              quinidine will increase the level or effect of paclitaxel by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • paclitaxel protein bound

              quinidine will increase the level or effect of paclitaxel protein bound by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • palbociclib

              quinidine will increase the level or effect of palbociclib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of palbociclib with strong CYP3A inhibitors. If unable to avoid, reduce palbociclib dose to 75 mg/day.

            • paliperidone

              quinidine will increase the level or effect of paliperidone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              quinidine and paliperidone both increase QTc interval. Avoid or Use Alternate Drug.

            • panobinostat

              quinidine and panobinostat both increase QTc interval. Avoid or Use Alternate Drug. Panobinostat is known to significantly prolong QT interval. Panobinostat prescribing information states use with drugs known to prolong QTc is not recommended.

            • paromomycin

              quinidine will increase the level or effect of paromomycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • paroxetine

              paroxetine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              paroxetine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

              quinidine and paroxetine both increase QTc interval. Avoid or Use Alternate Drug.

            • perphenazine

              quinidine, perphenazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • protriptyline

              protriptyline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • pexidartinib

              quinidine and pexidartinib both increase inhibition of GI absorption. Applies only to oral form of both agents. Avoid or Use Alternate Drug. Pexidartinib can cause hepatotoxicity. Avoid coadministration of pexidartinib with other products know to cause hepatoxicity.

              pexidartinib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Coadministration of pexidartinib (a CYP3A4 inducer) with sensitive CYP3A substrates may lead to serious therapeutic failures. If concomitant use is unavoidable, increase the CYP3A substrate dosage in accordance with approved product labeling.

            • pimavanserin

              pimavanserin and quinidine both increase QTc interval. Avoid or Use Alternate Drug. Coadministration may increase the risk of QT prolongation and cardiac arrhythmia.

            • pitolisant

              quinidine and pitolisant both increase QTc interval. Avoid or Use Alternate Drug.

            • pomalidomide

              quinidine increases levels of pomalidomide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

              quinidine increases levels of pomalidomide by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • ponatinib

              quinidine increases levels of ponatinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Decrease ponatinib starting dose to 30 mg qDay if coadministration with strong CYP3A4 inhibitors cannot be avoided.

            • ponesimod

              ponesimod, quinidine. Either increases effects of the other by QTc interval. Avoid or Use Alternate Drug. Consult cardiologist if considering treatment. Generally, should not be initiated in patients who are concurrently taking QT prolonging drugs with known arrhythmogenic properties, such as HR-lowering calcium channel blockers (eg, verapamil, diltiazem).

            • posaconazole

              posaconazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Use of posaconazole in combination with drugs that both prolong the QT interval and are substrates for CYP3A4 is contraindicated

              quinidine will increase the level or effect of posaconazole by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              quinidine and posaconazole both increase QTc interval. Avoid or Use Alternate Drug.

            • prednisolone

              quinidine will increase the level or effect of prednisolone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • prednisone

              quinidine will increase the level or effect of prednisone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • pretomanid

              quinidine, pretomanid. Either increases toxicity of the other by Other (see comment). Avoid or Use Alternate Drug. Comment: Pretomanid regimen associated with hepatotoxicity. Avoid alcohol and hepatotoxic agents, including herbal supplements and drugs other than bedaquiline and linezolid.

            • procainamide

              quinidine will increase the level or effect of procainamide by basic (cationic) drug competition for renal tubular clearance. Avoid or Use Alternate Drug.

            • prochlorperazine

              quinidine, prochlorperazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • promazine

              quinidine, promazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • promethazine

              quinidine, promethazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • propafenone

              quinidine will increase the level or effect of propafenone by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • propranolol

              quinidine will increase the level or effect of propranolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Monitor patients for hypotension, bradycardia, arrhythmias and heart failure.

            • ranolazine

              quinidine and ranolazine both increase QTc interval. Avoid or Use Alternate Drug.

            • red yeast rice

              quinidine will increase the level or effect of red yeast rice by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. May increase creatine kinase levels and increase risk of myopathy or rhabdomyolysis; red yeast rice contains monocolin K (reportedly identical to lovastatin)

            • ribociclib

              ribociclib and quinidine both increase QTc interval. Avoid or Use Alternate Drug.

            • rifabutin

              rifabutin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • rifampin

              rifampin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • rimegepant

              quinidine will increase the level or effect of rimegepant by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • riociguat

              quinidine will increase the level or effect of riociguat by decreasing metabolism. Avoid or Use Alternate Drug. Coadministration of riociguat (substrate of CYP isoenzymes 1A1, 2C8, 3A, 2J2) with strong CYP inhibitors may require a decreased initial dose of 0.5 mg PO TID; monitor for signs of hypotension and reduce dose if needed

              quinidine will increase the level or effect of riociguat by Other (see comment). Avoid or Use Alternate Drug. Coadministration of riociguat (an ABCG2 [BCRP] substrate) with strong ABCG2 inhibitors may require a decreased initial dose of 0.5 mg PO TID; monitor for signs of hypotension and reduce dose if needed

            • risperidone

              quinidine will increase the level or effect of risperidone by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              quinidine and risperidone both increase QTc interval. Avoid or Use Alternate Drug.

            • ritonavir

              quinidine will increase the level or effect of ritonavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              ritonavir increases levels of quinidine by decreasing metabolism. Contraindicated.

            • romidepsin

              quinidine will increase the level or effect of romidepsin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

              quinidine and romidepsin both increase QTc interval. Avoid or Use Alternate Drug.

            • ruxolitinib

              quinidine will increase the level or effect of ruxolitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Reduce ruxolitinib starting dose to 10 mg BID with platelet count 100 X 10^9/L or more and concurrent use of strong CYP3A4 inhibitors; avoid with platelet counts <100 X 10^9/L

            • saquinavir

              quinidine will increase the level or effect of saquinavir by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • selegiline transdermal

              selegiline transdermal and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • sertraline

              sertraline and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • St John's Wort

              dextromethorphan and St John's Wort both increase serotonin levels. Avoid or Use Alternate Drug.

            • silodosin

              quinidine will increase the level or effect of silodosin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • siponimod

              siponimod, quinidine. Either increases effects of the other by QTc interval. Avoid or Use Alternate Drug. Because of the potential additive effects on heart rate, siponimod should generally not be initiated in patients taking QT prolonging drugs with known arrhythmogenic properties, heart rate lowering calcium channel blockers, or other drugs that may decrease heart rate. If treatment considered, obtain cardiology consult regarding switching to non-heart-rate lowering drugs or appropriate monitoring for treatment initiation.

            • sirolimus

              quinidine will increase the level or effect of sirolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • sonidegib

              quinidine will increase the level or effect of sonidegib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sonidegib with strong CYP3A4 inhibitors.

            • sotorasib

              sotorasib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. If use is unavoidable, refer to the prescribing information of the CYP3A4 substrate for dosage modifications

              sotorasib will decrease the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If use is unavoidable, refer to the prescribing information of the P-gp substrate for dosage modifications.

            • squill

              quinidine increases toxicity of squill by pharmacodynamic synergism. Avoid or Use Alternate Drug.

            • St John's Wort

              St John's Wort will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • streptomycin

              quinidine will increase the level or effect of streptomycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • sulfamethoxazole

              quinidine and sulfamethoxazole both increase QTc interval. Avoid or Use Alternate Drug.

            • suvorexant

              quinidine increases levels of suvorexant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Suvorexant not recommended with use of strong CYP3A4 inhibitors.

            • tacrolimus

              quinidine will increase the level or effect of tacrolimus by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • tamsulosin

              quinidine increases levels of tamsulosin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

            • telavancin

              quinidine and telavancin both increase QTc interval. Avoid or Use Alternate Drug.

            • tepotinib

              tepotinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If concomitant use unavoidable, reduce the P-gp substrate dosage if recommended in its approved product labeling.

            • thioridazine

              quinidine will increase the level or effect of thioridazine by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              quinidine, thioridazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • timolol

              quinidine will increase the level or effect of timolol by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

            • tobramycin

              quinidine will increase the level or effect of tobramycin by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • tofacitinib

              quinidine increases levels of tofacitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Reduce tofacitinib dose to 5 mg qDay when coadministered with potent CYP3A4 inhibitors.

            • tolvaptan

              quinidine will increase the level or effect of tolvaptan by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug.

            • topotecan

              quinidine will increase the level or effect of topotecan by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. Product labeling for PO topotecan recommends avoiding concomitant use of P-gp inhibitors; the interaction with IV topotecan may be less severe but is still likely of clinical significance

            • toremifene

              quinidine and toremifene both increase QTc interval. Avoid or Use Alternate Drug. Concurrent use of toremifene with agents causing QT prolongation should be avoided. If concomitant use is required it's recommended that toremifene be interrupted. If interruption not possible, patients requiring therapy with a drug that prolongs QT should be closely monitored. ECGs should be obtained for high risk patients.

            • trazodone

              trazodone and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • trifluoperazine

              quinidine, trifluoperazine. Either increases effects of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Additive cardiac effects.

            • trimethoprim

              quinidine and trimethoprim both increase QTc interval. Avoid or Use Alternate Drug.

            • trimipramine

              trimipramine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • triptorelin

              triptorelin increases toxicity of quinidine by QTc interval. Avoid or Use Alternate Drug. Increases risk of torsades de pointes.

            • tropisetron

              quinidine and tropisetron both increase QTc interval. Avoid or Use Alternate Drug.

            • tucatinib

              tucatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Avoid concomitant use of tucatinib with CYP3A substrates, where minimal concentration changes may lead to serious or life-threatening toxicities. If unavoidable, reduce CYP3A substrate dose according to product labeling.

            • umeclidinium bromide/vilanterol inhaled

              quinidine increases toxicity of umeclidinium bromide/vilanterol inhaled by QTc interval. Avoid or Use Alternate Drug. Exercise extreme caution when vilanterol coadministered with drugs that prolong QTc interval; adrenergic agonist effects on the cardiovascular system may be potentiated.

            • vandetanib

              quinidine, vandetanib. Either increases toxicity of the other by QTc interval. Avoid or Use Alternate Drug. Avoid coadministration with drugs known to prolong QT interval; if a drug known to prolong QT interval must be used, more frequent ECG monitoring is recommended.

            • venetoclax

              quinidine will increase the level or effect of venetoclax by P-glycoprotein (MDR1) efflux transporter. Avoid or Use Alternate Drug. If a P-gp inhibitor must be used, reduce the venetoclax dose by at least 50%. Monitor more closely for signs of venetoclax toxicities.

            • venlafaxine

              quinidine and venlafaxine both increase QTc interval. Avoid or Use Alternate Drug.

              venlafaxine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug.

              venlafaxine and dextromethorphan both increase serotonin levels. Avoid or Use Alternate Drug.

            • vilanterol/fluticasone furoate inhaled

              quinidine increases toxicity of vilanterol/fluticasone furoate inhaled by QTc interval. Avoid or Use Alternate Drug. Exercise extreme caution when vilanterol coadministered with drugs that prolong QTc interval; adrenergic agonist effects on the cardiovascular system may be potentiated.

            • vilazodone

              dextromethorphan, vilazodone. Either increases toxicity of the other by serotonin levels. Avoid or Use Alternate Drug. Concomitant therapy should be discontinued immediately if signs or symptoms of serotonin syndrome emerge and supportive symptomatic treatment should be initiated. .

            Monitor Closely (287)

            • 5-HTP

              5-HTP and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • abiraterone

              abiraterone increases levels of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Avoid coadministration of abiraterone with substrates of CYP2D6. If alternative therapy cannot be used, exercise caution and consider a dose reduction of the CYP2D6 substrate.

            • acetazolamide

              acetazolamide will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

            • albuterol

              albuterol and quinidine both increase QTc interval. Use Caution/Monitor.

            • alfuzosin

              quinidine and alfuzosin both increase QTc interval. Use Caution/Monitor.

            • aliskiren

              quinidine will increase the level or effect of aliskiren by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • almotriptan

              almotriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • aluminum hydroxide

              aluminum hydroxide will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

            • alvimopan

              quinidine will increase the level or effect of alvimopan by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • amantadine

              quinidine will increase the level or effect of amantadine by decreasing renal clearance. Use Caution/Monitor. Coadministration of quinine or quinidine with amantadine was shown to reduce the renal clearance of amantadine by ~30%.

            • amiloride

              amiloride, quinidine. Mechanism: unspecified interaction mechanism. Use Caution/Monitor. Increased risk of arrhythmias in pts. with ventricular tachycardia.

            • amobarbital

              amobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • aprepitant

              aprepitant will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • arformoterol

              arformoterol and quinidine both increase QTc interval. Use Caution/Monitor.

            • aripiprazole

              dextromethorphan, aripiprazole. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

              quinidine will increase the level or effect of aripiprazole by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • armodafinil

              armodafinil will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              quinidine will increase the level or effect of armodafinil by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • artemether/lumefantrine

              artemether/lumefantrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • artemether

              artemether and quinidine both increase QTc interval. Use Caution/Monitor.

            • artemether/lumefantrine

              artemether/lumefantrine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • asenapine

              dextromethorphan, asenapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • atazanavir

              atazanavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • atomoxetine

              quinidine will increase the level or effect of atomoxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Reduced initial doses of atomoxetine are recommended with strong CYP2D6 inhibitors.

            • avapritinib

              quinidine will increase the level or effect of avapritinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • azithromycin

              quinidine and azithromycin both increase QTc interval. Modify Therapy/Monitor Closely.

            • bedaquiline

              quinidine and bedaquiline both increase QTc interval. Modify Therapy/Monitor Closely. ECG should be monitored closely

            • benzhydrocodone/acetaminophen

              quinidine will increase the level or effect of benzhydrocodone/acetaminophen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone [benzhydrocodone is prodrug of hydrocodone]) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

            • berotralstat

              quinidine increases levels of berotralstat by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Reduced berotralstat dose to 110 mg/day when coadministered with P-gp inhibitors.

              berotralstat will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor or titrate P-gp substrate dose if coadministered.

              berotralstat will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor or titrate substrate dose when berotralstat is coadministered with narrow therapeutic index drugs that are CYP3A substrates.

            • betrixaban

              quinidine increases levels of betrixaban by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Decrease betrixaban dose to 80 mg PO once, then 40 mg PO qDay if coadministered with a P-gp inhibitor.

            • blinatumomab

              blinatumomab increases levels of quinidine by decreasing metabolism. Modify Therapy/Monitor Closely. Treatment initiation causes transient release of cytokines that may suppress CYP450 enzymes; highest drug-drug interaction risk is during the first 9 days of the first cycle and the first 2 days of the 2nd cycle in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index.

            • bosentan

              bosentan will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • bosutinib

              bosutinib increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

              bosutinib and quinidine both increase QTc interval. Use Caution/Monitor.

            • brexpiprazole

              quinidine will increase the level or effect of brexpiprazole by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Administer half of the usual brexpiprazole dose when coadministered with strong CYP2D6 inhibitors. If also administered with a strong/moderate CYP3A4 inhibitor, administer a quarter of brexpiprazole dose. NOTE: In MDD clinical trials, brexpiprazole dosage was not adjusted for strong CYP2D6 inhibitors (eg, paroxetine, fluoxetine); thus, CYP considerations are already factored into general dosing recommendations and brexpiprazole may be administered without dosage adjustment in patients with MDD.

              quinidine will increase the level or effect of brexpiprazole by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Administer half of the usual brexpiprazole dose when coadministered with strong CYP3A4 inhibitors. If also administered with a strong/moderate CYP2D6 inhibitor, administer a quarter of brexpiprazole dose.

            • brodalumab

              brodalumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, brodalumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of brodalumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

            • budesonide

              budesonide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • bupivacaine implant

              quinidine, bupivacaine implant. Either increases toxicity of the other by Other (see comment). Use Caution/Monitor. Comment: Local anesthetics may increase the risk of developing methemoglobinemia when concurrently exposed to drugs that also cause methemoglobinemia.

            • bupropion

              bupropion will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • butabarbital

              butabarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • butalbital

              butalbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • calcium carbonate

              calcium carbonate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

            • capecitabine

              capecitabine and quinidine both increase QTc interval. Use Caution/Monitor.

            • cariprazine

              quinidine will increase the level or effect of cariprazine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration with strong CYP3A4 inhibitors requires cariprazine dose reduction. See Dosage Modification section in drug monograph.

              dextromethorphan, cariprazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • cenobamate

              cenobamate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Increase dose of CYP3A4 substrate, as needed, when coadministered with cenobamate.

            • clobazam

              clobazam will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Lower doses of drugs metabolized by CYP2D6 may be required when used concomitantly.

            • ceritinib

              quinidine increases levels of ceritinib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • chlorpromazine

              quinidine will increase the level or effect of chlorpromazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • ciprofloxacin

              ciprofloxacin and quinidine both increase QTc interval. Use Caution/Monitor. Ciprofloxacin elicits minimal effects on QT interval. Caution if used in combination with other drugs known to affect QT interval or in patients with other risk factors.

            • citalopram

              quinidine and citalopram both increase QTc interval. Use Caution/Monitor. ECG monitoring is recommended, along with drugs that may prolong the QT interval.

            • clozapine

              dextromethorphan, clozapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • cobicistat

              cobicistat will increase the level or effect of quinidine by Other (see comment). Modify Therapy/Monitor Closely. Quinidine is a substrate of CYP3A4 and P-gp, and inhibits CYP2D6 and P-gp; cobicistat is a substrate and inhibitor of both isoenzymes and a P-gp inhibitor

              cobicistat will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • cocaine

              cocaine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • codeine

              quinidine will decrease the level or effect of codeine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Prevents conversion of codeine to its active metabolite morphine.

            • conivaptan

              conivaptan will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • cortisone

              cortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • crofelemer

              crofelemer increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Crofelemer has the potential to inhibit CYP3A4 at concentrations expected in the gut; unlikely to inhibit systemically because minimally absorbed.

            • cyclosporine

              quinidine will increase the level or effect of cyclosporine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

              cyclosporine will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • dabigatran

              quinidine will increase the level or effect of dabigatran by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Atrial fibrillation: Avoid coadministering dabigatran with P-gp inhibitors if CrCl <30 mL/min. DVT/PE treatment: Avoid coadministering dabigatran with P-gp inhibitors if CrCl <50 mL/min

            • dabrafenib

              dabrafenib will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely.

            • darifenacin

              darifenacin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • darunavir

              darunavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • dasatinib

              dasatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • daunorubicin

              quinidine will increase the level or effect of daunorubicin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • deferasirox

              deferasirox will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • degarelix

              degarelix and quinidine both increase QTc interval. Use Caution/Monitor.

            • desvenlafaxine

              desvenlafaxine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Desvenlafaxine inhibits CYP2D6; with higher desvenlafaxine doses (ie, 400 mg) decrease the CYP2D6 substrate dose by up to 50%; no dosage adjustment needed with desvenlafaxine doses <100 mg

            • deutetrabenazine

              quinidine will increase the level or effect of deutetrabenazine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Strong CYP2D6 inhibitors increase the systemic exposure to the active dihydro-metabolites of deutetrabenazine by approximately 3-fold. Do not exceed 18 mg/dose and 36 mg/day of deutetrabenazine if coadministered with strong CYP2D6 inhibitors.

              quinidine and deutetrabenazine both increase QTc interval. Modify Therapy/Monitor Closely. Quinidine is a strong CYP2D6 inhibitor and also prolongs the QT interval. Strong CYP2D6 inhibitors increase the systemic exposure to the active dihydro-metabolites of deutetrabenazine by approximately 3-fold. Do not exceed 18 mg/dose and 36 mg/day of deutetrabenazine if coadministered with strong CYP2D6 inhibitors.

            • dexamethasone

              dexamethasone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • dexfenfluramine

              dexfenfluramine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

              quinidine will increase the level or effect of dexfenfluramine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • dextroamphetamine

              quinidine will increase the level or effect of dextroamphetamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              dextroamphetamine and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • dextromethorphan

              quinidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • dihydroergotamine

              dextromethorphan and dihydroergotamine both increase serotonin levels. Modify Therapy/Monitor Closely.

            • DHEA, herbal

              DHEA, herbal will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • dienogest/estradiol valerate

              quinidine will increase the level or effect of dienogest/estradiol valerate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor for potential adverse effects such as nausea, irregular uterine bleeding, breast tenderness and headache.

            • dihydroergotamine intranasal

              dextromethorphan and dihydroergotamine intranasal both increase serotonin levels. Modify Therapy/Monitor Closely.

            • diltiazem

              diltiazem will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              quinidine will increase the level or effect of diltiazem by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • donepezil

              quinidine will increase the level or effect of donepezil by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • doxorubicin

              quinidine will increase the level or effect of doxorubicin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • doxorubicin liposomal

              quinidine will increase the level or effect of doxorubicin liposomal by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • dronedarone

              dronedarone will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • dulaglutide

              dulaglutide, quinidine. Other (see comment). Use Caution/Monitor. Comment: Dulaglutide slows gastric emptying and may impact absorption of concomitantly administered oral medications; be particularly cautious when coadministered with drugs that have a narrow therapeutic index.

            • dupilumab

              dupilumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, dupilumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of dupilumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

            • duvelisib

              duvelisib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration with duvelisib increases AUC of a sensitive CYP3A4 substrate which may increase the risk of toxicities of these drugs. Consider reducing the dose of the sensitive CYP3A4 substrate and monitor for signs of toxicities of the coadministered sensitive CYP3A substrate.

              quinidine will increase the level or effect of duvelisib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • efavirenz

              efavirenz will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • elagolix

              elagolix will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

              elagolix decreases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Elagolix is a weak-to-moderate CYP3A4 inducer. Monitor CYP3A substrates if coadministered. Consider increasing CYP3A substrate dose if needed.

            • eletriptan

              eletriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • eliglustat

              eliglustat increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Monitor therapeutic drug concentrations, as indicated, or consider reducing the dosage of the P-gp substrate and titrate to clinical effect.

            • eluxadoline

              quinidine increases levels of eluxadoline by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. As a precautionary measure due to incomplete information on the metabolism of eluxadoline, use caution when coadministered with strong CYP2D6 inhibitors.

              eluxadoline increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Caution when CYP3A substrates that have a narrow therapeutic index are coadministered with eluxadoline.

            • elvitegravir

              quinidine increases levels of elvitegravir by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Elvitegravir is a CYP3A4 substrate; if coadministered with strong CYP3A4 inhibitors may increase levels.

            • elvitegravir/cobicistat/emtricitabine/tenofovir DF

              elvitegravir/cobicistat/emtricitabine/tenofovir DF increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Cobicistat is a CYP3A4 inhibitor; contraindicated with CYP3A4 substrates for which elevated plasma concentrations are associated with serious and/or life-threatening events.

            • encainide

              quinidine will increase the level or effect of encainide by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • encorafenib

              encorafenib, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Encorafenib both inhibits and induces CYP3A4 at clinically relevant plasma concentrations. Coadministration of encorafenib with sensitive CYP3A4 substrates may result in increased toxicity or decreased efficacy of these agents.

            • enzalutamide

              enzalutamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • ergotamine

              dextromethorphan and ergotamine both increase serotonin levels. Modify Therapy/Monitor Closely.

            • eslicarbazepine acetate

              eslicarbazepine acetate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • estrogens esterified

              quinidine will increase the level or effect of estrogens esterified by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely.

            • ethotoin

              ethotoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

            • etoposide

              quinidine will increase the level or effect of etoposide by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • etravirine

              etravirine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • ezogabine

              ezogabine, quinidine. Either increases toxicity of the other by QTc interval. Use Caution/Monitor. Slight and transient QT-prolongation observed with ezogabine, particularly when dose titrated to 1200 mg/day. QT interval should be monitored when ezogabine is prescribed with agents known to increase QT interval.

            • fedratinib

              fedratinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Adjust dose of drugs that are CYP3A4 substrates as necessary.

            • fenfluramine

              dextromethorphan and fenfluramine both increase serotonin levels. Modify Therapy/Monitor Closely.

              fenfluramine, dextromethorphan. Either increases effects of the other by serotonin levels. Use Caution/Monitor. Coadministration with drugs that increase serotoninergic effects may increase the risk of serotonin syndrome.

            • ferric maltol

              ferric maltol, quinidine. Either increases levels of the other by unspecified interaction mechanism. Modify Therapy/Monitor Closely. Coadministration of ferric maltol with certain oral medications may decrease the bioavailability of either ferric maltol and some oral drugs. For oral drugs where reductions in bioavailability may cause clinically significant effects on its safety or efficacy, separate administration of ferric maltol from these drugs. Duration of separation may depend on the absorption of the medication concomitantly administered (eg, time to peak concentration, whether the drug is an immediate or extended release product).

            • fesoterodine

              quinidine will increase the level or effect of fesoterodine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • fexofenadine

              quinidine will increase the level or effect of fexofenadine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • finerenone

              quinidine will increase the level or effect of finerenone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Monitor serum potassium during initiation and dosage adjustment of either finererone or weak CYP3A4 inhibitors. Adjust finererone dosage as needed.

            • fludrocortisone

              fludrocortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • fluphenazine

              quinidine will increase the level or effect of fluphenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              dextromethorphan, fluphenazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • fluticasone furoate

              quinidine will increase the level or effect of fluticasone furoate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Strong CYP3A4 inhibitors may increase fluticasone systemic exposure

            • frovatriptan

              frovatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • fluticasone inhaled

              quinidine will increase the level or effect of fluticasone inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Strong CYP3A4 inhibitors may increase fluticasone systemic exposure

            • fluvoxamine

              quinidine will increase the level or effect of fluvoxamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • fosamprenavir

              fosamprenavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • fosphenytoin

              fosphenytoin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              fosphenytoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

            • fostamatinib

              fostamatinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Concomitant use of fostamatinib may increase concentrations of P-gp substrates. Monitor for toxicities of the P-gp substrate drug that may require dosage reduction when given concurrently with fostamatinib.

            • fostemsavir

              quinidine and fostemsavir both increase QTc interval. Use Caution/Monitor. QTc prolongation reported with higher than recommended doses of fostemsavir.

            • galantamine

              quinidine will increase the level or effect of galantamine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • gefitinib

              quinidine increases levels of gefitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Coadministration of strong CYP3A4 inhibitors may increase risk for gefitinib adverse effects.

            • gemtuzumab

              quinidine and gemtuzumab both increase QTc interval. Use Caution/Monitor.

            • glecaprevir/pibrentasvir

              quinidine will increase the level or effect of glecaprevir/pibrentasvir by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

              glecaprevir/pibrentasvir will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • glycerol phenylbutyrate

              glycerol phenylbutyrate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Glycerol phenylbutyrate is a weak inducer of CYP3A4. Monitor for decreased efficacy of CYP3A4 substrates that have a narrow therapeutic index.

            • grapefruit

              grapefruit will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • griseofulvin

              griseofulvin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • guselkumab

              guselkumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, normalizing the formation of CYP450 enzymes. Upon initiation or discontinuation of guselkumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

            • haloperidol

              dextromethorphan, haloperidol. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • hawthorn

              hawthorn increases effects of quinidine by pharmacodynamic synergism. Use Caution/Monitor.

            • henbane

              henbane, quinidine. unspecified interaction mechanism. Use Caution/Monitor. Combination not recommended by British Herbal Medicine Association.

            • hydrochlorothiazide

              quinidine will increase the level or effect of hydrochlorothiazide by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • hydrocodone

              quinidine will increase the level or effect of hydrocodone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Hydromorphone (<3% of the circulating parent hydrocodone) is mainly formed by CYP2D6 mediated O-demethylation of hydrocodone. Hydromorphone may contribute to the total analgesic effect of hydrocodone.

            • hydrocortisone

              hydrocortisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • iloperidone

              iloperidone increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Iloperidone is a time-dependent CYP3A inhibitor and may lead to increased plasma levels of drugs predominantly eliminated by CYP3A4.

              dextromethorphan, iloperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • incobotulinumtoxinA

              quinidine, incobotulinumtoxinA. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Use of anticholinergic drugs after administration of botulinum toxin-containing products may potentiate systemic anticholinergic effects.

            • L-tryptophan

              dextromethorphan and L-tryptophan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • isoniazid

              dextromethorphan and isoniazid both increase serotonin levels. Modify Therapy/Monitor Closely.

            • indacaterol, inhaled

              indacaterol, inhaled, quinidine. QTc interval. Use Caution/Monitor. Drugs that are known to prolong the QTc interval may have an increased the risk of ventricular arrhythmias.

            • indinavir

              indinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • isoniazid

              isoniazid will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • istradefylline

              istradefylline will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Istradefylline 40 mg/day increased peak levels and AUC of CYP3A4 substrates in clinical trials. This effect was not observed with istradefylline 20 mg/day. Consider dose reduction of sensitive CYP3A4 substrates.

              istradefylline will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Istradefylline 40 mg/day increased peak levels and AUC of P-gp substrates in clinical trials. Consider dose reduction of sensitive P-gp substrates.

            • ivacaftor

              ivacaftor increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Ivacaftor and its M1 metabolite has the potential to inhibit P-gp; may significantly increase systemic exposure to sensitive P-gp substrates with a narrow therapeutic index.

            • ixekizumab

              ixekizumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, ixekizumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of ixekizumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

            • lacosamide

              quinidine, lacosamide. Either increases levels of the other by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Consider decreasing lacosamide dose when coadministered with strong CYP3A4 inhibitors.

            • lapatinib

              lapatinib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • lemborexant

              quinidine will increase the level or effect of lemborexant by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Lower nightly dose of lemborexant recommended if coadministered with weak CYP3A4 inhibitors. See drug monograph for specific dosage modification.

            • lenvatinib

              quinidine and lenvatinib both increase QTc interval. Use Caution/Monitor. Lenvatinib prescribing information recommends monitoring ECG closely when coadministered with QT prolonging drugs.

            • letermovir

              letermovir increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              letermovir increases levels of dextromethorphan by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • levomilnacipran

              quinidine will increase the level or effect of levomilnacipran by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Do not exceed 80 mg/day of levomilnacipran when coadministered with strong CYP3A4 inhibitors

            • lithium

              dextromethorphan and lithium both increase serotonin levels. Modify Therapy/Monitor Closely.

            • lofexidine

              quinidine will increase the level or effect of lofexidine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Concomitant use of lofexidine with strong CYP2D6 inhibitors may increase lofexidine plasma levels. Monitor for symptoms of orthostasis and bradycardia if coadministered with a CYP2D6 inhibitor. Consider lofexidine dose reduction.

              quinidine and lofexidine both increase QTc interval. Use Caution/Monitor. ECG monitoring is recommended.

            • lomitapide

              lomitapide increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Consider reducing dose when used concomitantly with lomitapide.

            • lonafarnib

              lonafarnib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Lonafarnib is a weak P-gp inhibitor. Monitor for adverse reactions if coadministered with P-gp substrates where minimal concentration changes may lead to serious or life-threatening toxicities. Reduce P-gp substrate dose if needed.

            • loratadine

              quinidine will increase the level or effect of loratadine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              quinidine will increase the level or effect of loratadine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • loxapine

              dextromethorphan, loxapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • loxapine inhaled

              dextromethorphan, loxapine inhaled. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • lsd

              dextromethorphan and lsd both increase serotonin levels. Modify Therapy/Monitor Closely.

            • lumacaftor/ivacaftor

              quinidine increases levels of lumacaftor/ivacaftor by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Strong CYP3A inhibitors do not impact lumacaftor exposure, but increased ivacaftor exposure by 4.3-fold. Due to the induction effect of lumacaftor on CYP3A, at steady-state the net exposure of ivacaftor is not expected to exceed that when given in the absence of lumacaftor at a dose of 150 mg q12hr (the approved dose of ivacaftor monotherapy). Therefore, no dose adjustment is necessary when CYP3A inhibitors are initiated in patients currently taking lumacaftor/ivacaftor. However, when initiating lumacaftor/ivacaftor in patients taking strong CYP3A inhibitors, reduce the dose to 1 tablet daily (lumacaftor 200 mg/ivacaftor 125 mg total daily dose) for the first week of treatment to allow for the steady-state induction effect of lumacaftor. Following this period, continue with the recommended daily dose. No dose adjustment is required for moderate or weak CYP3A4 inhibitors.

            • lumefantrine

              lumefantrine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              lumefantrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • lurasidone

              dextromethorphan, lurasidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • maraviroc

              quinidine will increase the level or effect of maraviroc by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Decrease maraviroc dose to 150 mg BID when coadministered with strong CYP3A4 inhibitors

            • marijuana

              marijuana will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • medroxyprogesterone

              quinidine will increase the level or effect of medroxyprogesterone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Use alternative if available.

            • memantine

              quinidine will increase the level or effect of memantine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • metformin

              quinidine will increase the level or effect of metformin by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • methyclothiazide

              quinidine will increase the level or effect of methyclothiazide by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • methylprednisolone

              methylprednisolone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • metronidazole

              metronidazole will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • miconazole vaginal

              miconazole vaginal will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • midazolam intranasal

              quinidine will increase the level or effect of midazolam intranasal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Coadministration of mild CYP3A4 inhibitors with midazolam intranasal may cause higher midazolam systemic exposure, which may prolong sedation.

            • midodrine

              quinidine will increase the level or effect of midodrine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • mirtazapine

              dextromethorphan and mirtazapine both increase serotonin levels. Modify Therapy/Monitor Closely.

            • mitotane

              mitotane decreases toxicity of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Mitotane is a strong inducer of cytochrome P-4503A4; monitor when coadministered with CYP3A4 substrates for possible dosage adjustments.

            • modafinil

              modafinil will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • molindone

              dextromethorphan, molindone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • morphine

              dextromethorphan and morphine both increase serotonin levels. Modify Therapy/Monitor Closely.

            • nafcillin

              nafcillin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • naldemedine

              quinidine increases levels of naldemedine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor naldemedine for potential adverse effects if coadministered with P-gp inhibitors.

            • naratriptan

              naratriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • nelfinavir

              nelfinavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • netupitant/palonosetron

              quinidine will increase the level or effect of netupitant/palonosetron by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Netupitant is mainly metabolized by CYP3A4; no dosage adjustment is required

            • nevirapine

              nevirapine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • nifedipine

              nifedipine will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              nifedipine decreases levels of quinidine by increasing elimination. Use Caution/Monitor.

              quinidine increases levels of nifedipine by decreasing metabolism. Use Caution/Monitor.

            • nintedanib

              quinidine increases levels of nintedanib by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. If nintedanib adverse effects occur, management may require interruption, dose reduction, or discontinuation of therapy .

            • ofloxacin

              quinidine will increase the level or effect of ofloxacin by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • olanzapine

              dextromethorphan, olanzapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • oliceridine

              quinidine will increase the level or effect of oliceridine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. If concomitant use is necessary, may require less frequent oliceridine dosing. Closely monitor for respiratory depression and sedation and titrate subsequent doses accordingly. If inhibitor is discontinued, consider increase oliceridine dosage until stable drug effects are achieved. Monitor for signs of opioid withdrawal.

            • olodaterol inhaled

              quinidine and olodaterol inhaled both increase QTc interval. Use Caution/Monitor. Drugs that prolong the QTc interval and may potentiate the effects of beta2 agonists on the cardiovascular system; increased risk of ventricular arrhythmias

            • ombitasvir/paritaprevir/ritonavir & dasabuvir

              ombitasvir/paritaprevir/ritonavir & dasabuvir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Caution is warranted and therapeutic concentration monitoring (if available) is recommended for antiarrhythmics when coadministered with Viekira Pak

            • oritavancin

              oritavancin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Oritavancin is a weak CYP3A4 inducer; caution if coadministered with CYP3A4 substrates that have a narrow therapeutic index

            • osilodrostat

              osilodrostat and quinidine both increase QTc interval. Use Caution/Monitor.

            • osimertinib

              osimertinib and quinidine both increase QTc interval. Use Caution/Monitor. Conduct periodic monitoring with ECGs and electrolytes in patients taking drugs known to prolong the QTc interval.

            • ospemifene

              quinidine increases levels of ospemifene by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • oxaliplatin

              oxaliplatin will increase the level or effect of quinidine by Other (see comment). Use Caution/Monitor. Monitor for ECG changes if therapy is initiated in patients with drugs known to prolong QT interval.

            • oxcarbazepine

              oxcarbazepine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • oxycodone

              quinidine decreases effects of oxycodone by decreasing metabolism. Use Caution/Monitor. Decreased conversion of hydrocodone to active metabolite morphine.

            • ozanimod

              ozanimod and quinidine both increase QTc interval. Modify Therapy/Monitor Closely. The potential additive effects on heart rate, treatment with ozanimod should generally not be initiated in patients who are concurrently treated with QT prolonging drugs with known arrhythmogenic properties.

            • palbociclib

              palbociclib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. The dose of sensitive CYP3A substrates with a narrow therapeutic index may need to be reduced if coadministered with palbociclib

            • paliperidone

              dextromethorphan, paliperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • panobinostat

              panobinostat will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Panobinostat can increase the levels and effects of sensitive CYP2D6 substrates or those with a narrow therapeutic index CYP2D6.

              quinidine increases levels of panobinostat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Reduce panobinostat starting dose to 10 mg if coadministered with strong CYP3A4 inhibitors.

            • paroxetine

              quinidine will increase the level or effect of paroxetine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Monitor patients for signs of paroxetine toxicity. Paroxetine doses may need to be reduced.

            • pazopanib

              pazopanib increases levels of dextromethorphan by decreasing metabolism. Use Caution/Monitor.

            • pasireotide

              quinidine and pasireotide both increase QTc interval. Modify Therapy/Monitor Closely.

            • pazopanib

              quinidine and pazopanib both increase QTc interval. Modify Therapy/Monitor Closely.

            • peginterferon alfa 2b

              peginterferon alfa 2b, dextromethorphan. Other (see comment). Use Caution/Monitor. Comment: When patients are administered peginterferon alpha-2b with CYP2D6 substrates, the therapeutic effect of these drugs may be altered. Peginterferon alpha-2b may increase or decrease levels of CYP2D6 substrate.

            • pentazocine

              dextromethorphan and pentazocine both increase serotonin levels. Modify Therapy/Monitor Closely.

            • pentobarbital

              pentobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • perhexiline

              quinidine will increase the level or effect of perhexiline by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • perphenazine

              dextromethorphan, perphenazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

              quinidine will increase the level or effect of perphenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • phenobarbital

              phenobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • pimavanserin

              dextromethorphan, pimavanserin. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • phenytoin

              phenytoin will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              phenytoin decreases levels of quinidine by increasing metabolism. Use Caution/Monitor.

            • pimozide

              dextromethorphan, pimozide. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • pitolisant

              quinidine will increase the level or effect of pitolisant by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. If coadministered with strong CYP2D6 inhibitors, initiate pitolisant at 8.9 mg/day and increase after 7 days to maximum of 17.8 mg/day. For patients currently taking pitolisant, reduce pitolisant dose by half upon initiating strong CYP2D6 inhibitors.

              pitolisant will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Pitolisant is a borderline/weak inducer of CYP3A4. Monitor sensitive CYP3A4 substrates for reduced effectiveness if coadministered.

            • ponatinib

              ponatinib increases levels of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • pramipexole

              quinidine will increase the level or effect of pramipexole by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • prednisone

              prednisone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • primidone

              primidone will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • prochlorperazine

              quinidine will increase the level or effect of prochlorperazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • promazine

              quinidine will increase the level or effect of promazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • promethazine

              quinidine will increase the level or effect of promethazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • quetiapine

              quetiapine, quinidine. Either increases toxicity of the other by QTc interval. Use Caution/Monitor. Avoid use with drugs that prolong QT and in patients with risk factors for prolonged QT interval. Postmarketing cases show QT prolongation with overdose in patients with concomitant illness or with drugs known to cause electrolyte imbalance or prolong QT.

              dextromethorphan, quetiapine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • quinidine

              quinidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • quinine

              quinidine will increase the level or effect of quinine by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

              quinidine and quinine both increase QTc interval. Use Caution/Monitor.

            • quinupristin/dalfopristin

              quinupristin/dalfopristin will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • ribociclib

              ribociclib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Caution if ribociclib is coadministered with sensitive CYP3A4 substrates that have a narrow therapeutic index. Dose reduction for sensitive CYP3A4 substrates may be needed.

            • rifapentine

              rifapentine will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • rifaximin

              quinidine increases levels of rifaximin by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • rilpivirine

              rilpivirine increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Rilpivirine should be used with caution when co-administered with a drug with a known risk of Torsade de Pointes.

            • rimabotulinumtoxinB

              quinidine, rimabotulinumtoxinB. Either increases effects of the other by pharmacodynamic synergism. Use Caution/Monitor. Anticholinergics may enhance botulinum toxin effects. Closely monitor for increased neuromuscular blockade.

            • risperidone

              dextromethorphan, risperidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

              quinidine will increase the level or effect of risperidone by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • ritonavir

              ritonavir will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • rizatriptan

              rizatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • rivaroxaban

              quinidine increases levels of rivaroxaban by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Patients with renal impairment receiving rivaroxaban with drugs that are combined P-gp and weak or moderate CYP3A4 inhibitors may have significant increases in exposure compared with patients with normal renal function and no inhibitor use, since both pathways of rivaroxaban elimination are affected. Since these increases may increase bleeding risk, use rivaroxaban in this situation only if the potential benefit justifies the potential risk.

            • rolapitant

              rolapitant will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Monitor for adverse reactions when unable to avoid coadministration with narrow therapeutic index CYP2D6 substrates.

            • SAMe

              dextromethorphan and SAMe both increase serotonin levels. Modify Therapy/Monitor Closely.

            • rucaparib

              rucaparib will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Adjust dosage of CYP3A4 substrates, if clinically indicated.

            • rufinamide

              rufinamide will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • sarecycline

              sarecycline will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Monitor for toxicities of P-gp substrates that may require dosage reduction when coadministered with P-gp inhibitors.

            • sarilumab

              sarilumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of cytokines such as IL-6. Elevated IL-6 concentration may down-regulate CYP activity, such as in patients with RA, and, hence, increase drug levels compared with subjects without RA. Blockade of IL-6 signaling by IL-6 antagonists (eg, sarilumab) might reverse the inhibitory effect of IL-6 and restore CYP activity, leading to decreased drug concentrations. Caution when initiating or discontinuing sarilumab if coadministered with CYP450 substrates, especially those with a narrow therapeutic index.

            • saxagliptin

              quinidine will increase the level or effect of saxagliptin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Limit saxagliptin dose to 2.5 mg/day when coadministered with strong CYP3A4 inhibitors

            • schisandra

              schisandra will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • secobarbital

              secobarbital will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • secukinumab

              secukinumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, secukinumab could normalize the formation of CYP450 enzymes. Upon initiation or discontinuation of secukinumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

            • selpercatinib

              selpercatinib increases toxicity of quinidine by QTc interval. Use Caution/Monitor.

            • sevelamer

              sevelamer decreases levels of quinidine by increasing elimination. Use Caution/Monitor.

            • siltuximab

              siltuximab, quinidine. Other (see comment). Use Caution/Monitor. Comment: CYP450 activity in the liver is down regulated by infection and inflammation stimuli including cytokines (eg, IL-6); inhibition of IL-6 by siltuximab may restore CYP450 enzymatic activity; caution if coadministered with CYP substrates that have a narrow therapeutic index.

            • sodium bicarbonate

              sodium bicarbonate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

            • sodium citrate/citric acid

              sodium citrate/citric acid will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor. Elevated quinidine plasma levels, possibly with cardiac conduction disturbances and arrhythmias, may occur.

            • sodium lactate

              sodium lactate will increase the level or effect of quinidine by passive renal tubular reabsorption - basic urine. Use Caution/Monitor.

            • sodium sulfate/?magnesium sulfate/potassium chloride

              sodium sulfate/?magnesium sulfate/potassium chloride increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Consider predose and post-colonoscopy ECGs in patients at increased risk of serious cardiac arrhythmias. .

            • sodium sulfate/potassium sulfate/magnesium sulfate

              sodium sulfate/potassium sulfate/magnesium sulfate increases toxicity of quinidine by QTc interval. Use Caution/Monitor. Consider predose and post-colonoscopy ECGs in patients at increased risk of serious cardiac arrhythmias. .

            • sofosbuvir/velpatasvir

              sofosbuvir/velpatasvir increases levels of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Velpatasvir inhibits CYP3A4. Caution if coadministered with drugs with narrow therapeutics indexes.

            • sorafenib

              sorafenib and quinidine both increase QTc interval. Use Caution/Monitor.

            • stiripentol

              stiripentol, quinidine. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Stiripentol is a CYP3A4 inhibitor and inducer. Monitor CYP3A4 substrates coadministered with stiripentol for increased or decreased effects. CYP3A4 substrates may require dosage adjustment.

              stiripentol will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Modify Therapy/Monitor Closely. Consider reducing the dose of P-glycoprotein (P-gp) substrates, if adverse reactions are experienced when administered concomitantly with stiripentol.

            • sulfamethoxazole

              quinidine will increase the level or effect of sulfamethoxazole by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • sumatriptan

              sumatriptan and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • sumatriptan intranasal

              sumatriptan intranasal and dextromethorphan both increase serotonin levels. Modify Therapy/Monitor Closely.

            • talazoparib

              quinidine will increase the level or effect of talazoparib by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Talazoparib is a P-glycoprotein (P-gp) substrate; coadministration with P-gp inhibitors may increase talazoparib systemic exposure.

            • tamoxifen

              quinidine decreases effects of tamoxifen by decreasing metabolism. Use Caution/Monitor. Inhibition of CYP2D6 metabolism to tamoxifen's active metabolite, endoxifen.

            • tamsulosin

              quinidine increases levels of tamsulosin by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • tasimelteon

              quinidine will increase the level or effect of tasimelteon by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • tazemetostat

              tazemetostat will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              quinidine will increase the level or effect of tazemetostat by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • tecovirimat

              tecovirimat will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Tecovirimat is a weak CYP3A4 inducer. Monitor sensitive CYP3A4 substrates for effectiveness if coadministered.

            • teduglutide

              teduglutide increases levels of quinidine by Other (see comment). Use Caution/Monitor. Comment: Teduglutide may increase absorption of concomitant PO medications; caution with with drugs requiring titration or those with a narrow therapeutic index; dose adjustment may be necessary.

            • telotristat ethyl

              telotristat ethyl will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Telotristat ethyl induces CYP3A4 and may reduce systemic exposure of sensitive CYP3A4 substrates. Monitor for suboptimal efficacy and consider increasing the dose of the CYP3A4 substrate.

            • teniposide

              quinidine will increase the level or effect of teniposide by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor.

            • tenofovir DF

              tenofovir DF, quinidine. Either increases levels of the other by decreasing renal clearance. Use Caution/Monitor.

            • tetrabenazine

              quinidine increases effects of tetrabenazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Decrease tetrabenazine dose by 50% when coadministered with strong CYP2D6 inhibitors.

            • thiothixene

              dextromethorphan, thiothixene. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • tinidazole

              quinidine will increase the level or effect of tinidazole by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • tobramycin inhaled

              tobramycin inhaled and quinidine both increase nephrotoxicity and/or ototoxicity. Modify Therapy/Monitor Closely. Avoid concurrent or sequential use to decrease risk for ototoxicity

            • tolterodine

              quinidine will increase the level or effect of tolterodine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • topiramate

              topiramate will decrease the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • tramadol

              quinidine decreases effects of tramadol by decreasing metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.

              quinidine decreases effects of tramadol by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Decreased conversion of tramadol to active metabolite.

              dextromethorphan and tramadol both increase serotonin levels. Modify Therapy/Monitor Closely.

            • triamterene

              quinidine will increase the level or effect of triamterene by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • trifluoperazine

              dextromethorphan, trifluoperazine. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            • triclabendazole

              triclabendazole and quinidine both increase QTc interval. Use Caution/Monitor.

            • trifluoperazine

              quinidine will increase the level or effect of trifluoperazine by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • trimethoprim

              quinidine will increase the level or effect of trimethoprim by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • tropisetron

              quinidine will increase the level or effect of tropisetron by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

            • tucatinib

              tucatinib will increase the level or effect of quinidine by P-glycoprotein (MDR1) efflux transporter. Use Caution/Monitor. Consider reducing the dosage of P-gp substrates, where minimal concentration changes may lead to serious or life-threatening toxicities.

            • umeclidinium bromide/vilanterol inhaled

              quinidine will increase the level or effect of umeclidinium bromide/vilanterol inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Vilanterol is a CYP3A4 substrate; coadministration with potent CYP3A4 inhibitors may increase systemic exposure

            • ustekinumab

              ustekinumab, quinidine. Other (see comment). Use Caution/Monitor. Comment: Formation of CYP450 enzymes can be altered by increased levels of certain cytokines during chronic inflammation; thus, normalizing the formation of CYP450 enzymes. Upon initiation or discontinuation of ustekinumab in patients who are receiving concomitant CYP450 substrates, particularly those with a narrow therapeutic index, consider monitoring for therapeutic effect.

            • valbenazine

              quinidine will increase the level or effect of valbenazine by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Consider reducing valbenazine dose based on tolerability if coadministered with a strong CYP2D6 inhibitor.

            • vemurafenib

              vemurafenib and quinidine both increase QTc interval. Modify Therapy/Monitor Closely. Concomitant use of vemurafenib with drugs that prolong QT interval is not recommended. Quinidine may also increase vemurafenib levels.

            • verapamil

              verapamil will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              quinidine will increase the level or effect of verapamil by basic (cationic) drug competition for renal tubular clearance. Use Caution/Monitor.

            • vilanterol/fluticasone furoate inhaled

              quinidine will increase the level or effect of vilanterol/fluticasone furoate inhaled by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Fluticasone furoate and vilanterol are both CYP3A4 substrates; coadministration with potent CYP3A4 inhibitors may increase systemic exposure

            • voclosporin

              voclosporin, quinidine. Either increases effects of the other by QTc interval. Use Caution/Monitor.

            • warfarin

              quinidine increases effects of warfarin by decreasing metabolism. Use Caution/Monitor. Dosage reduction of warfarin may be needed during concurrent administration of quinidine. Monitor INR and adjust the dosage accordingly.

            • zafirlukast

              zafirlukast will increase the level or effect of quinidine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

            • ziprasidone

              dextromethorphan, ziprasidone. unspecified interaction mechanism. Use Caution/Monitor. Serotonin modulators may enhance dopamine blockade, possibly increasing the risk for neuroleptic malignant syndrome. Antipsychotics may enhance serotonergic effect of serotonin modulators, which may result in serotonin syndrome. Monitor for evidence of serotonin toxicity (eg, mental status changes, autonomic instability, and neuromuscular hyperactivity) or neuroleptic malignant syndrome (eg, hyperthermia, muscle rigidity, autonomic dysfunction).

            Minor (43)

            • ambrisentan

              quinidine will increase the level or effect of ambrisentan by P-glycoprotein (MDR1) efflux transporter. Minor/Significance Unknown.

            • amiodarone

              amiodarone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • antithrombin alfa

              quinidine increases effects of antithrombin alfa by decreasing metabolism. Minor/Significance Unknown.

            • antithrombin III

              quinidine increases effects of antithrombin III by decreasing metabolism. Minor/Significance Unknown.

            • argatroban

              quinidine increases effects of argatroban by decreasing metabolism. Minor/Significance Unknown.

            • asenapine

              asenapine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • atracurium

              quinidine increases effects of atracurium by pharmacodynamic synergism. Minor/Significance Unknown.

            • bemiparin

              quinidine increases effects of bemiparin by decreasing metabolism. Minor/Significance Unknown.

            • bivalirudin

              quinidine increases effects of bivalirudin by decreasing metabolism. Minor/Significance Unknown.

            • celecoxib

              celecoxib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • chloroquine

              chloroquine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • cimetidine

              cimetidine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • cisatracurium

              quinidine increases effects of cisatracurium by pharmacodynamic synergism. Minor/Significance Unknown.

            • dalteparin

              quinidine increases effects of dalteparin by decreasing metabolism. Minor/Significance Unknown.

            • darifenacin

              darifenacin will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • diphenhydramine

              diphenhydramine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • dronedarone

              dronedarone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • enoxaparin

              quinidine increases effects of enoxaparin by decreasing metabolism. Minor/Significance Unknown.

            • fondaparinux

              quinidine increases effects of fondaparinux by decreasing metabolism. Minor/Significance Unknown.

            • haloperidol

              haloperidol will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • heparin

              quinidine increases effects of heparin by decreasing metabolism. Minor/Significance Unknown.

            • imatinib

              imatinib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • lily of the valley

              quinidine, lily of the valley. Either increases toxicity of the other by pharmacodynamic synergism. Minor/Significance Unknown.

            • maraviroc

              maraviroc will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • marijuana

              marijuana will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • nilotinib

              nilotinib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • onabotulinumtoxinA

              quinidine increases effects of onabotulinumtoxinA by pharmacodynamic synergism. Minor/Significance Unknown.

            • pancuronium

              quinidine increases effects of pancuronium by pharmacodynamic synergism. Minor/Significance Unknown.

            • parecoxib

              parecoxib will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • perphenazine

              perphenazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • phenindione

              quinidine increases effects of phenindione by decreasing metabolism. Minor/Significance Unknown.

            • propafenone

              propafenone will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • protamine

              quinidine increases effects of protamine by decreasing metabolism. Minor/Significance Unknown.

            • quinacrine

              quinacrine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • ranolazine

              ranolazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • rapacuronium

              quinidine increases effects of rapacuronium by pharmacodynamic synergism. Minor/Significance Unknown.

            • ritonavir

              ritonavir will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • rocuronium

              quinidine increases effects of rocuronium by pharmacodynamic synergism. Minor/Significance Unknown.

            • sertraline

              sertraline will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • succinylcholine

              quinidine increases effects of succinylcholine by pharmacodynamic synergism. Minor/Significance Unknown.

            • thioridazine

              thioridazine will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • tipranavir

              tipranavir will increase the level or effect of dextromethorphan by affecting hepatic enzyme CYP2D6 metabolism. Minor/Significance Unknown.

            • vecuronium

              quinidine increases effects of vecuronium by pharmacodynamic synergism. Minor/Significance Unknown.

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            Adverse Effects

            >10%

            Diarrhea (13%)

            1-10%

            Dizziness (10%)

            Cough (5%)

            Vomiting (5%)

            Asthenia (5%)

            Peripheral edema (5%)

            Increased gamma-glutamyltransferase (3%)

            Flatulence (3%)

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            Warnings

            Contraindications

            Hypersensitivity

            History of quinine, mefloquine, or quinidine-induced thrombocytopenia, hepatitis, bone marrow depression, or lupus-like syndrome

            Concomitant use with drugs containing quinidine, quinine, or mefloquine

            Coadministration of MAOIs or use within 14 d

            Drugs that both prolong QT interval and are metabolized by CYP2D6 (eg, thioridazine, pimozide)

            Complete AV block (without implanted pacemakers)

            Prolonged QT interval, congenital long QT syndrome, or history of torsades de pointes or heart failure

            Cautions

            Quinidine can cause immune-mediated thrombocytopenia (discontinue if thrombocytopenia occurs)

            Hepatotoxicity reported within first few weeks following initiation of quinidine

            Monitor for QTc prolongation if concomitant use of drugs taht prolong QT interval cannot be avoided or concomitant CYP3A4 used

            Quinidine may cause anticholinergic effects and exacerbate certain conditions (eg, myasthenia gravis)

            Monitor ECG in patients with left ventricular hypertrophy or left ventricular dysfunction

            Dextromethorphan may cause serotonergic effects; monitor for worsening in myasthenia gravis and other sensitive conditions

            Use caution with CYP2D6 poor metabolizers

            CYP3A4 inhibitors may increase quinidine serum levels and risk for QT prolongation

            Coadministration with CYP2D6 substrates other than dextromethorphan that cause accumulation of parent drug and/or failure of metabolite formation may decrease safety and/or efficacy of concomitant CYPD6 metabolized drugs; adjust dose of CYPD6 substrate or use alternative therapy when indicated

            Concomitant use of dextromethorphan with serotonergic drugs (eg, SSRIs, TCAs) may increase risk for serotonin syndrome

            Quinidine may increase digoxin levels (as much as double) by inhibiting P-glycoprotein

            Coadministration with alcohol or other CNS depressants may cause additive effects

            May cause dizziness; use precautions to reduce falls

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            Pregnancy & Lactation

            Pregnancy

            There are no adequate data on the developmental risk associated with use in pregnant women

            Animal studies

            • In oral studies conducted in rats and rabbits, a combination of dextromethorphan/quinidine demonstrated developmental toxicity, including teratogenicity (rabbits) and embryolethality, when given to pregnant animals
            • When administered to female rats during pregnancy and lactation, pup survival and pup weight were decreased at all doses, and developmental delay was observed in offspring at the mid and high doses

            Lactation

            Quinidine is excreted in human milk; unknown whether dextromethorphan is excreted in human milk

            There are no data on the effects of quinidine or dextromethorphan on the breastfed infant or the effects on milk production

            There are no data on effects of quinidine or dextromethorphan on breastfed infant or on milk production

            Developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for therapy and any potential adverse effects on breastfed infant from therapy or from underlying maternal condition

            Pregnancy Categories

            A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA: Information not available.

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            Pharmacology

            Mechanism of Action

            The mechanism by which dextromethorphan exerts therapeutic effects in patients with pseudobulbar affect is unknown

            Dextromethorphan (DM) is a sigma-1 receptor agonist and an uncompetitive NMDA receptor antagonist

            Quinidine increases plasma levels of dextromethorphan by competitively inhibiting cytochrome P4502D6, which catalyzes a major biotransformation pathway for dextromethorphan

            Pharmacokinetics

            Half-Life: 13 hr (dextromethorphan); 7 hr (quinidine)

            Peak Plasma Time: 3-4 hr (dextromethorphan); 1-2 hr (quinidine)

            Protein Bound: 60-70% ((dextromethorphan); 80-89% (quinidine)

            Metabolism: dextromethorphan by CYP2D6; quinidine’s primary pharmacological action in is to competitively inhibit the metabolism of dextromethorphan catalyzed by CYP2D6 in order to increase and prolong plasma concentrations of dextromethorphan; quinidine metabolized by CYP3A4

            Excretion: Urine

            Pharmacogenomics

            The quinidine component is intended to inhibit CYP2D6 so that higher exposure to dextromethorphan can be achieved compared to when dextromethorphan is given alone

            Approximately 7-10% of Caucasians and 3-8% of African Americans lack the capacity to metabolize CYP2D6 substrates and are classified as poor metabolizers (PMs)

            The quinidine component is not expected to contribute to effectiveness in PMs, but adverse events of the quinidine are still possible

            In those patients who may be at risk of significant toxicity due to quinidine, genotyping to determine if they are PMs should be considered prior to making the decision to treat

            Genetic testing laboratories

            • Genotyping tests for CYP2D6 variants are commercially available through the following companies
            • Applied Biosystems (http://www.appliedbiosystems.com/)
            • GenPath Diagnostics (http://www.genpathdiagnostics.com/)
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            Administration

            Oral Administration

            May take with or without food

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            Images

            No images available for this drug.
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            Patient Handout

            A Patient Handout is not currently available for this monograph.
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            Formulary

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            The above information is provided for general informational and educational purposes only. Individual plans may vary and formulary information changes. Contact the applicable plan provider for the most current information.

            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
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            NC NOT COVERED – Drugs that are not covered by the plan.
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            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.