tamoxifen (Rx)

Brand and Other Names:Soltamox
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Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

tablet (generic)

  • 10mg
  • 20mg

oral solution

  • 10mg/5mL (Soltamox)

Breast Cancer

Metastatic breast cancer

  • Indicated for the treatment of adults with estrogen receptor-positive metastatic breast cancer
  • 20-40 mg/day PO; doses >20mg/day should be divided BID (ie, morning and evening)
  • Although the FDA has approved a dosage range of 20-40 mg/day, clinical benefit for doses >20 mg/day has not been demonstrated

Adjuvant breast cancer

  • Indicated for adjuvant treatment of adults with early stage estrogen receptor-positive breast cancer and to reduce occurrence of contralateral breast cancer in adults when used as adjuvant therapy for breast cancer
  • Recommended dose: 20 mg PO qDay for 5-10 years
  • Doses >20 mg/day yield no additional clinical benefit

Ductal Carcinoma in Situ

Indicated in women with ductal carcinoma in situ (DCIS) following breast surgery and radiation to reduce the risk of invasive breast cancer

20 mg PO qDay for 5 years

Breast Cancer Prevention

Indicated to reduce the incidence of breast cancer in women at high risk for breast cancer; high risk is defined as women aged ≥35 years with a 5-year predicted risk of breast cancer ≥1.67% (calculated by the Gail Model)

20 mg PO qDay for 5 years

Data are limited for use >5 yr in the risk-reduction setting (NCCN guidelines)

Ovulation Induction (Off-label)

5-40 mg PO q12hr for 4 days

Mastalgia (Off-label)

10 mg PO qDay for 4 months

Other Indications & Uses

Gynecomastia

Safety and efficacy not established

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              • abametapir

                abametapir will increase the level or effect of tamoxifen 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.

              • afatinib

                tamoxifen 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.

              • anastrozole

                tamoxifen decreases levels of anastrozole by unspecified interaction mechanism. Contraindicated. Anastrozole and tamoxifen should not be administered together.

              • apalutamide

                apalutamide will decrease the level or effect of tamoxifen 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.

              • atazanavir

                atazanavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • bosutinib

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

              • cobicistat

                cobicistat decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Affecting hepatic/intestinal enzyme CYP3A4 metabolism. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • conivaptan

                conivaptan, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • dacomitinib

                dacomitinib will increase the level or effect of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Avoid or Use Alternate Drug. Avoid use with CYP2D6 substrates where minimal increases in concentration of the CYP2D6 substrate may lead to serious or life-threatening toxicities.

              • darunavir

                darunavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • edoxaban

                tamoxifen 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

              • enzalutamide

                enzalutamide decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. affecting hepatic/intestinal enzyme CYP3A4 metabolism. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • fexinidazole

                fexinidazole decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Fexinidazole inhibits CYP3A4, and thereby decreases metabolism of tamoxifen to active metabolites.

              • fosamprenavir

                fosamprenavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • idelalisib

                idelalisib decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Contraindicated. Affects hepatic/intestinal enzyme CYP3A4 metabolism. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • iloperidone

                iloperidone decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • indinavir

                indinavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • ivosidenib

                ivosidenib will decrease the level or effect of tamoxifen 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.

                ivosidenib will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Avoid or Use Alternate Drug. Avoid coadministration of sensitive CYP2C9 substrates with ivosidenib or replace with alternate therapies. If coadministration is unavoidable, monitor patients for loss of therapeutic effect of these drugs.

              • letrozole

                tamoxifen decreases levels of letrozole by unspecified interaction mechanism. Contraindicated. Letrozole should not be given concurrently with tamoxifen. Letrozole therapy after the completion of standard tamoxifen treatment is not associated with impaired effects of letrozole.

              • lonafarnib

                lonafarnib will increase the level or effect of tamoxifen 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.

                tamoxifen 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.

              • lopinavir

                lopinavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • mefloquine

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

              • mitotane

                mitotane decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug.

              • nefazodone

                nefazodone, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • nelfinavir

                nelfinavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • pomalidomide

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

              • ribociclib

                ribociclib increases levels of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. Concurrent use of ribociclib and tamoxifen is not indicated. Coadministration shown to increase tamoxifen AUC and Cmax. May increase risk of adverse effects.

              • riociguat

                tamoxifen 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

              • ritonavir

                ritonavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • saquinavir

                saquinavir, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Avoid or Use Alternate Drug. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • topotecan

                tamoxifen 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

              • tucatinib

                tamoxifen will increase the level or effect of tucatinib by Other (see comment). Avoid or Use Alternate Drug. Coadministration of tucatinib (a CYP2C8 substrate) with a strong or moderate CYP2C8 inhibitors increases tucatinib plasma concentrations and risk of toxicities.

                tucatinib will increase the level or effect of tamoxifen 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.

              • venetoclax

                tamoxifen 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.

              • warfarin

                tamoxifen increases effects of warfarin by unknown mechanism. Avoid or Use Alternate Drug.

              Monitor Closely (121)

              • abiraterone

                abiraterone, tamoxifen. affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. CYP2D6 inhibition decreases metabolism of tamoxifen to hydroxytamoxifen, and N-desmethyl tamoxifen to endoxifen (active metabolites with 100-fold greater affinity for estrogen receptor); decreased endoxifen levels may result in poor clinical outcome.

              • alpelisib

                alpelisib will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely.

              • amiodarone

                amiodarone, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

              • amobarbital

                amobarbital, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

                amobarbital, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • apalutamide

                apalutamide will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Coadministration of apalutamide, a weak CYP2C9 inducer, with drugs that are CYP2C9 substrates can result in lower exposure to these medications. Evaluate for loss of therapeutic effect if medication must be coadministered.

              • atogepant

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

              • avapritinib

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

              • axitinib

                tamoxifen increases levels of axitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              • bosentan

                bosentan will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • bupropion

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

                bupropion will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Inhibition of CYP2D6 decreases metabolism of tamoxifen to active metabolite, endoxifen

              • butabarbital

                butabarbital will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • cannabidiol

                cannabidiol will increase the level or effect of tamoxifen by decreasing metabolism. Modify Therapy/Monitor Closely. Cannabidiol may potentially inhibit CYP2C9 activity. Consider reducing the dose when concomitantly using CYP2C9 substrates.

              • carbamazepine

                carbamazepine will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • celecoxib

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

              • cenobamate

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

              • ceritinib

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

              • chloroquine

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

              • chlorpromazine

                chlorpromazine, tamoxifen. affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. CYP2D6 inhibition decreases metabolism of tamoxifen to hydroxytamoxifen, and N-desmethyl tamoxifen to endoxifen (active metabolites with 100-fold greater affinity for estrogen receptor); decreased endoxifen levels may result in poor clinical outcome.

              • cimetidine

                cimetidine, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • cinacalcet

                cinacalcet, tamoxifen. affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. CYP2D6 inhibition decreases metabolism of tamoxifen to hydroxytamoxifen, and N-desmethyl tamoxifen to endoxifen (active metabolites with 100-fold greater affinity for estrogen receptor); decreased endoxifen levels may result in poor clinical outcome.

              • clarithromycin

                clarithromycin, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • cocaine

                cocaine, tamoxifen. affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. CYP2D6 inhibition decreases metabolism of tamoxifen to hydroxytamoxifen, and N-desmethyl tamoxifen to endoxifen (active metabolites with 100-fold greater affinity for estrogen receptor); decreased endoxifen levels may result in poor clinical outcome.

              • crizotinib

                crizotinib, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • crofelemer

                crofelemer increases levels of tamoxifen 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.

              • dabigatran

                tamoxifen 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 tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely.

              • dasatinib

                dasatinib, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • deferasirox

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

              • dexamethasone

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

              • dexmedetomidine

                dexmedetomidine, tamoxifen. affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. CYP2D6 inhibition decreases metabolism of tamoxifen to hydroxytamoxifen, and N-desmethyl tamoxifen to endoxifen (active metabolites with 100-fold greater affinity for estrogen receptor); decreased endoxifen levels may result in poor clinical outcome.

              • dienogest/estradiol valerate

                tamoxifen 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.

              • diltiazem

                diltiazem, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • diphenhydramine

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

              • dronedarone

                dronedarone, tamoxifen. affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • duloxetine

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

              • duvelisib

                duvelisib will increase the level or effect of tamoxifen 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.

              • efavirenz

                efavirenz, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

                efavirenz, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • eliglustat

                eliglustat increases levels of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Monitor therapeutic drug concentrations, as indicated, or consider reducing the dosage of the concomitant drug and titrate to clinical effect.

              • elvitegravir/cobicistat/emtricitabine/tenofovir DF

                elvitegravir/cobicistat/emtricitabine/tenofovir DF decreases levels of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. Cobicistat is a CYP3A4 inhibitor; may decrease conversion of tamoxifen to active metabolite.

                elvitegravir/cobicistat/emtricitabine/tenofovir DF decreases levels of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Cobicistat is a CYP2D6 inhibitor; may decrease conversion of tamoxifen to active metabolite.

              • encorafenib

                encorafenib, tamoxifen. 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.

              • erythromycin base

                erythromycin base, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • erythromycin ethylsuccinate

                erythromycin ethylsuccinate, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • erythromycin lactobionate

                erythromycin lactobionate, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • erythromycin stearate

                erythromycin stearate, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • eslicarbazepine acetate

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

              • etravirine

                etravirine, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

                etravirine, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • fedratinib

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

                fedratinib will increase the level or effect of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Adjust dose of drugs that are CYP2D6 substrates as necessary.

              • finerenone

                tamoxifen 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.

              • flibanserin

                tamoxifen will increase the level or effect of flibanserin by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Increased flibanserin adverse effects may occur if coadministered with multiple weak CYP3A4 inhibitors.

              • fluconazole

                fluconazole, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

              • fluoxetine

                fluoxetine will decrease the level or effect of tamoxifen by decreasing metabolism. Use Caution/Monitor. Inhibition of CYP2D6 metabolism to tamoxifen's active metabolite, endoxifen.

              • fluvoxamine

                fluvoxamine, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Decreases tamoxifen metabolism to active metabolites.

              • fosphenytoin

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

              • glecaprevir/pibrentasvir

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

              • grapefruit

                grapefruit, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • haloperidol

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

              • imatinib

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

              • isavuconazonium sulfate

                tamoxifen will increase the level or effect of isavuconazonium sulfate by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              • isoniazid

                isoniazid, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • itraconazole

                itraconazole will increase the level or effect of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Closely. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity)

              • ivacaftor

                tamoxifen increases levels of ivacaftor by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Monitor when coadministered with weak CYP3A4 inhibitors .

              • ketoconazole

                ketoconazole, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

                ketoconazole, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • leflunomide

                leflunomide, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

              • lemborexant

                tamoxifen 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.

              • letermovir

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

              • lomitapide

                tamoxifen increases levels of lomitapide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Lomitapide dose should not exceed 30 mg/day.

              • lorcaserin

                lorcaserin will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              • lorlatinib

                lorlatinib decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              • lumacaftor/ivacaftor

                lumacaftor/ivacaftor, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. In vitro studies suggest that lumacaftor may induce and ivacaftor may inhibit CYP2C9 substrates. .

              • lurasidone

                tamoxifen increases levels of lurasidone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. Concurrent use of weak CYP3A4 inhibitors can theoretically lead to an increased risk of lurasidone-related adverse reactions.

              • maraviroc

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

              • metronidazole

                metronidazole, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • midazolam intranasal

                tamoxifen 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.

              • mifepristone

                mifepristone decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. ketoconazole, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • mipomersen

                mipomersen, tamoxifen. Either increases toxicity of the other by Other (see comment). Use Caution/Monitor. Comment: Both drugs have potential to increase hepatic enzymes; monitor LFTs.

              • mirabegron

                mirabegron will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor.

              • modafinil

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

              • nafcillin

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

              • naldemedine

                tamoxifen 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.

              • nevirapine

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

              • nilotinib

                nilotinib, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

                nilotinib, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • nintedanib

                tamoxifen 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 .

              • nitisinone

                nitisinone will increase the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. Nitisinone inhibits CYP2C9. Caution if CYP2C9 substrate coadministered, particularly those with a narrow therapeutic index.

              • omeprazole

                omeprazole will increase the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

              • oxcarbazepine

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

              • paroxetine

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

              • peginterferon alfa 2b

                peginterferon alfa 2b decreases levels of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. When patients are administered peginterferon alpha-2b with CYP2C9 substrates, the therapeutic effect of these drugs may be altered. .

              • pentobarbital

                pentobarbital will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • perphenazine

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

              • phenobarbital

                phenobarbital will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • phenytoin

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

              • posaconazole

                posaconazole, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • primidone

                primidone will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • propafenone

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

              • quinidine

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

              • rifabutin

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

              • rifampin

                rifampin will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • rifapentine

                rifapentine will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • rifaximin

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

              • ritonavir

                ritonavir, tamoxifen. affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. CYP2D6 inhibition decreases metabolism of tamoxifen to hydroxytamoxifen, and N-desmethyl tamoxifen to endoxifen (active metabolites with 100-fold greater affinity for estrogen receptor); decreased endoxifen levels may result in poor clinical outcome.

              • rivaroxaban

                tamoxifen 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 tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Use Caution/Monitor. Rolapitant may increase plasma concentrations of CYP2D6 substrates for at least 28 days following rolapitant administration.

              • rucaparib

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

                rucaparib will increase the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Modify Therapy/Monitor Closely. Adjust dosage of CYP2C9 substrates, if clinically indicated.

              • saquinavir

                saquinavir, tamoxifen. Either increases effects of the other by QTc interval. Use Caution/Monitor.

              • secobarbital

                secobarbital will decrease the level or effect of tamoxifen by affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor.

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

              • selexipag

                tamoxifen will increase the level or effect of selexipag by decreasing metabolism. Modify Therapy/Monitor Closely. Reduce selexipag dose to once daily if coadministered with moderate CYP2C8 inhibitors.

              • sertraline

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

              • siponimod

                siponimod and tamoxifen both increase immunosuppressive effects; risk of infection. Use Caution/Monitor. Caution if coadministered because of additive immunosuppressive effects during such therapy and in the weeks following administration. When switching from drugs with prolonged immune effects, consider the half-life and mode of action of these drugs to avoid unintended additive immunosuppressive effects.

              • St John's Wort

                St John's Wort will decrease the level or effect of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              • stiripentol

                stiripentol, tamoxifen. 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.

              • sulfamethoxazole

                sulfamethoxazole, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

              • tazemetostat

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

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

              • terbinafine

                terbinafine will increase the level or effect of tamoxifen by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Assess need to reduce dose of CYP2D6-metabolized drug.

              • tinidazole

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

              • tipranavir

                tipranavir decreases effects of tamoxifen by decreasing metabolism. Use Caution/Monitor. Inhibition of CYP3A4 metabolism to tamoxifen's active metabolite, endoxifen.

                tipranavir decreases effects of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor.

              • vemurafenib

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

              • venlafaxine

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

              • verapamil

                verapamil will increase the level or effect of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity)

              • vilazodone

                tamoxifen increases levels of vilazodone by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. No dose adjustment needed with mild CYP3A4 inhibitors.

              • voriconazole

                voriconazole, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

                voriconazole, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Monitor. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • zafirlukast

                zafirlukast, tamoxifen. affecting hepatic enzyme CYP2C9/10 metabolism. Use Caution/Monitor. CYP2C9/10 inhibition decreases tamoxifen metabolism to active metabolites.

              Minor (12)

              • aprepitant

                aprepitant, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • artemether/lumefantrine

                artemether/lumefantrine will decrease the level or effect of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown.

              • black cohosh

                black cohosh increases effects of tamoxifen by pharmacodynamic synergism. Minor/Significance Unknown.

              • butalbital

                butalbital will decrease the level or effect of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown.

              • fluconazole

                fluconazole, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • lapatinib

                lapatinib, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • maitake

                maitake increases effects of tamoxifen by pharmacodynamic synergism. Minor/Significance Unknown. Maitake mushroom has anti-tumor effects (animal/in vitro research).

              • marijuana

                marijuana will increase the level or effect of tamoxifen by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown.

              • nifedipine

                nifedipine, tamoxifen. affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown. CYP3A4 inhibition decreases metabolism of tamoxifen to N-desmethyl tamoxifen (active metabolite with similar biologic activity).

              • ruxolitinib

                tamoxifen will increase the level or effect of ruxolitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Minor/Significance Unknown.

              • taurine

                tamoxifen decreases levels of taurine by unspecified interaction mechanism. Minor/Significance Unknown.

              • wheat germ extract

                wheat germ extract increases effects of tamoxifen by pharmacodynamic synergism. Minor/Significance Unknown. Determined by mfr. of Avemar to be a beneficial combination in ER+ breast cancer.

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              Adverse Effects

              >10%

              Hot flashes (64%)

              Vaginal discharge (30%)

              Amenorrhea (16%)

              Menstrual changes (13%)

              1-10%

              Oligomenorrhea (9%)

              Cataracts (8%)

              Bone pain (6%)

              Nausea (5%)

              Cough (4%)

              Edema (4%)

              Fatigue (4%)

              Musculoskeletal pain (3%)

              Ovarian cyst (3%)

              Depression (2%)

              Abdominal cramps (1%)

              Anorexia (1%)

              <1%

              Angioedema

              Corneal changes

              Loss of libido

              Endometrial cancer

              Pancreatitis

              Retinal vein thrombosis

              Stroke

              Uterine fibroids

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              Warnings

              Black Box Warnings

              Uterine malignancies and thromboembolic events

              • Serious and life-threatening events associated with tamoxifen in the risk reduction setting (women at high risk for cancer and women with DCIS) include uterine malignancies, stroke and pulmonary embolism
              • Fatal cases of each type of event have occurred
              • Discuss potential benefits versus risks of these serious events with women at high risk of breast cancer and women with DCIS considering tamoxifen to reduce their risk of developing breast cancer; benefits of tamoxifen citrate tablets outweigh its risks in women already diagnosed with breast cancer

              Contraindications

              Hypersensitivity

              Pregnancy

              Undiagnosed vaginal bleeding

              Patients who require concomitant warfarin therapy or have a history of deep vein thrombosis or pulmonary embolus if indication for treatment is either reduction of breast cancer incidence in high-risk patients or risk reduction of invasive breast cancer after treatment of DCIS

              Cautions

              Liver cancer and changes in liver enzyme levels reported with use; on rare occasions, a spectrum of more severe liver abnormalities including fatty liver, cholestasis, hepatitis and hepatic necrosis, that have included fatalities, also reported; monitor liver function periodically

              Unknown whether an increased risk for other (non-uterine) cancers is associated with tamoxifen

              Hypercalcemia reported in some breast cancer patients with bone metastases within a few weeks of starting treatment; if hypercalcemia occurs, treat as appropriate; if hypercalcemia is severe, discontinue therapy

              CYP2D6 polymorphism-CYP2D6 converts tamoxifen to active metabolite endoxifen; lowered CYP2D6 activity or concomitant CYP2D6 inhibitors may reduce tamoxifen efficacy

              Decreases in platelet counts, usually to 50,000-100,000/mm3, infrequently lower, reported in patients receiving therapy for breast cancer; hemorrhagic episodes have occurred, but not certain if episodes were due to tamoxifen therapy; leukopenia, sometimes in association with anemia and/or thrombocytopenia reported; neutropenia and pancytopenia also reported; perform periodic complete blood counts, including platelet counts

              Ocular disturbances, including corneal changes, decrement in color vision perception, retinal vein thrombosis, and retinopathy reported; an increased incidence of cataracts and need for cataract surgery reported; patients should seek medical attention if they experience visual disturbance

              Increased incidence of thromboembolic events (eg, deep vein thrombosis, pulmonary embolism), during tamoxifen therapy; when tamoxifen is coadministered with chemotherapy, there is further increase in risk of thromboembolic events; for treatment of breast cancer, carefully consider risks and benefits of tamoxifen in women with a history of thromboembolic events; advise patients to seek medical attention immediately if signs or symptoms of a thromboembolic event occur

              Increased incidence of uterine malignancies (endometrial adenocarcinoma and uterine sarcoma), including fatal cases, reported; underlying mechanism unknown, most uterine malignancies seen with tamoxifen are classified as adenocarcinoma of the endometrium; however, uterine sarcomas, including malignant mixed mullerian tumors (MMMT), generally associated with a higher FIGO stage (III/IV), also reported; uterine sarcoma at diagnosis usually associated with poor prognosis, and short survival; uterine sarcoma reported to occur more frequently among long-term users (≥2 years) of tamoxifen than non-users

              Associated with changes in bone mineral density; effect may depend on menstrual status; may be associated with protective effect on bone mineral density (BMD) in postmenopausal women; preventive loss may last over the 5 year treatment period; conversely, a decline in BMD reported in premenopausal women who continued to menstruate; may be associated with increased risk of fractures

              Hypercholesterolemia and hypertriglyceridemia reported; monitor cholesterol and triglycerides in patients with preexisting hyperlipidemia

              Fetal harm may occur when administered to pregnant woman (see Pregnancy)

              Perform periodic CBC, including platelet counts, and periodic liver function tests during therapy treatment with tamoxifen and for 9 months following the last dose

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              Pregnancy & Lactation

              Pregnancy

              Fetal harm may occur when administered to a pregnant woman

              FDA re-evaluated genotoxicity data, postmarketing reports, and published literature and found that tamoxifen was genotoxic in nonhuman studies, and results were inconclusive in human studies; available data from postmarketing reports and published literature from women who became pregnant 2-9 months after their last dose of tamoxifen have not identified a drug-associated risk of major birth defects or adverse maternal or fetal outcomes

              Animal studies

              • In rat and rabbit studies, doses of tamoxifen less than or equal to human doses resulted in increased embryotoxicity, abortions, and altered learning behaviors in the offspring; rodent models showed reproductive tract changes often associated with diethylstilbestrol (DES) in offspring of both sexes
              • Based on animal studies, tamoxifen may impair embryo implantation in females of reproductive potential, however, may not reliably cause infertility; advise women that tamoxifen does not always cause infertility, even in the presence of menstrual irregularity

              Contraception

              • Confirm pregnancy test in females of reproductive potential before initiation
              • Females: Advise females of reproductive potential to use effective non-hormonal contraception during treatment and for 2 months following the last dose

              Infertility

              • Based on animal studies, tamoxifen may impair embryo implantation in females of reproductive potential, however, may not reliably cause infertility
              • Advise women that tamoxifen does not always cause infertility, even in the presence of menstrual irregularity

              Lactation

              Tamoxifen reported to inhibit lactation

              Two placebo-controlled studies in over 150 women have shown that tamoxifen significantly inhibits early postpartum milk production; both studies tamoxifen was administered within 24 hr of delivery for between 5 and 18 days; effect of tamoxifen on established milk production is not known

              There are no data that address whether tamoxifen is excreted into human milk; direct neonatal exposure of tamoxifen to mice and rats (not via breast milk) produced 1) reproductive tract lesions in female rodents (similar to those seen in humans after intrauterine exposure to diethylstilbestrol) and 2) functional defects of the reproductive tract in male rodents such as testicular atrophy and arrest of spermatogenesis

              Unknown if tamoxifen is excreted in human milk

              Because of potential for serious adverse reactions in nursing infants from tamoxifen, women taking tamoxifen should not breast feed

              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

              Selective estrogen receptor modulator: nonsteroid with potent antiestrogenic effects in breast (but may be estrogen agonist in uterus); has cytostatic effect rather than cytocidal effects (cells accumulate in Go and G1 phase of the cell cycle)

              Pharmacokinetics

              Half-Life: 7-14 hr

              Peak Plasma Time: 3-6 hr

              Protein binding: 99%

              Peak Plasma Concentration: 40 ng/mL

              Metabolism: by hepatic P450 enzyme CYP2C9, CYP2D6, CYP3A4

              Metabolites: N-desmethyl tamoxifen, endoxifen

              Excretion: Feces (65%), urine (9%)

              Pharmacogenomics

              Metabolized via CYP2D6 into endoxifen (4-OH-N-desmethyl-tamoxifen), its primary active metabolite

              Lowered CYP2D6 activity or concomitant CYP2D6 inhibitors may reduce tamoxifen efficacy

              Poor CYP2D6 metabolizers are defined as those with *4/*4 alleles

              On October 18, 2006, the Pharmaceutical Science Clinical Pharmacology Subcommittee of the FDA recommended including information on CYP2D6 genotypes and their potential effect on patient outcomes in the label for tamoxifen, but they did not come to consensus on whether testing should be recommended or considered optional

              Subsequent to that recommendation, branded tamoxifen (Nolvadex) was discontinued and no further guidance was given by FDA on whether to amend the label for generic tamoxifen

              Recent data presented at the 2010 San Antonio Breast Cancer Symposium found the CYP2D6 allele status had no effect on any outcomes, including disease recurrence, distant recurrence, and overall survival

              Further research will help elucidate the potential effect of strong CYP2D6 inhibitors, such as SSRIs, on tamoxifen metabolism, but there is no evidence to suggest that the use of such medications should influence the use of tamoxifen

              Therefore, based on the data available to date, routine testing for CYP2D6 variants is not recommended

              CYP2C19 heterozygous *2 carriership may be a predictive factor for patients with breast cancer using tamoxifen; this factor was associated with a longer survival among tamoxifen users in a recent study (Pharmacogenomics. 2010;11[10]:1367-75)

              Genetic testing laboratories

              • The Roche Cytochrome AmpliChip P450 2D6/2C19 Genotyping and Phenotyping Assay can be used to identify 26 different alleles of CYP2D6, including *4
              • The following companies offer testing for CYP2D6 variants
              • DxS (http://www.dxsdiagnostics.com/)
              • LabCorp (http://www.labcorp.com/)
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              Images

              BRAND FORM. UNIT PRICE PILL IMAGE
              Soltamox oral
              -
              20 mg/10 mL solution
              tamoxifen oral
              -
              20 mg tablet
              tamoxifen oral
              -
              10 mg tablet
              tamoxifen oral
              -
              20 mg tablet
              tamoxifen oral
              -
              10 mg tablet
              tamoxifen oral
              -
              10 mg tablet
              tamoxifen oral
              -
              20 mg tablet
              tamoxifen oral
              -
              10 mg tablet
              tamoxifen oral
              -
              20 mg tablet
              tamoxifen oral
              -
              10 mg tablet

              Copyright © 2010 First DataBank, Inc.

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              Patient Handout

              Patient Education
              tamoxifen oral

              TAMOXIFEN - ORAL

              (ta-MOX-ih-fen)

              COMMON BRAND NAME(S): Nolvadex, Soltamox

              WARNING: Tamoxifen has rarely caused very serious (possibly fatal) strokes, blood clots in the lungs/legs, and cancer of the uterus. If you are taking tamoxifen to reduce the risk of breast cancer, or if your cancer is limited to the milk ducts (ductal carcinoma in situ-DCIS), then discuss the benefits and risks of taking this medication with your doctor. However, if you are taking tamoxifen to treat breast cancer, then the benefits of taking tamoxifen are greater than the risks of side effects.Get medical help right away if you develop symptoms of a stroke or blood clots in the lungs/legs, such as weakness on one side of the body, trouble speaking, sudden vision changes, confusion, shortness of breath, chest pain, or calf pain/swelling.Tell your doctor right away if you develop symptoms of cancer of the uterus, such as unusual changes in your monthly period (such as the amount or timing of bleeding), unusual vaginal discharge, or pain/pressure below your "belly button" (navel).

              USES: Tamoxifen is used to treat breast cancer. It is also used to reduce the chances of breast cancer in high-risk patients.This medication can block the growth of breast cancer. It works by interfering with the effects of estrogen in the breast tissue.

              HOW TO USE: Read the Medication Guide provided by your pharmacist before you start using tamoxifen and each time you get a refill. If you have any questions, consult your doctor or pharmacist.Take this medication by mouth with or without food, usually once or twice daily for 5 years, or as directed by your doctor. Daily dosages greater than 20 milligrams are usually divided in half and taken twice a day, in the morning and evening, or as directed by your doctor. If you are using the liquid, measure the dose carefully using a special measuring device/spoon. Do not use a household spoon because you may not get the correct dose.Dosage is based on your medical condition and response to treatment. The duration of treatment to prevent cancer from returning may be between 5 to 10 years, depending on your medical condition and response to treatment.Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time(s) each day.If you have breast cancer that has spread to other parts of the body, you may experience increased bone/cancer pain and/or disease flare-up as you start taking tamoxifen. In some cases, this may be a sign of a good response to the medication. Symptoms include increased bone pain, increased tumor size, or even new tumors. These symptoms usually disappear quickly. In any case, report these symptoms right away to your doctor.Since this drug can be absorbed through the skin and lungs, women who are pregnant or who may become pregnant should not handle this medication or breathe the dust from the tablets. (See also Precautions section.)Inform your doctor right away if your condition worsens (e.g., you get new breast lumps).

              SIDE EFFECTS: See also Warning section.Hot flashes, nausea, leg cramps, muscle aches, hair thinning, headache, and numb/tingling skin may occur. A loss of sexual ability/interest may occur in men. If these effects persist or worsen, notify your doctor promptly.Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.Tell your doctor right away if you have any serious side effects, including: vision changes (e.g., blurred vision), eye pain, easy bruising/bleeding, mental/mood changes, swelling of ankles/feet, unusual tiredness, signs of infection (e.g., fever, persistent sore throat), signs of liver disease (e.g., nausea/vomiting that doesn't stop, loss of appetite, stomach/abdominal pain, yellowing eyes/skin, dark urine).A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.In the US -Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

              PRECAUTIONS: Before taking tamoxifen, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.Before using this medication, tell your doctor or pharmacist your medical history, especially of: blood clots (e.g., deep vein thrombosis, pulmonary embolism, stroke), high cholesterol/triglycerides, limited or no ability to walk (immobility), diabetes, high blood pressure, smoking, cataracts, liver disease.Before having surgery (especially breast reconstruction), tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).Tell your doctor if you are pregnant or plan to become pregnant. You should not become pregnant while using tamoxifen. Tamoxifen may harm an unborn baby. Women using this medication should ask about reliable non-hormonal forms of birth control (such as condoms, diaphragms with spermicide) during treatment and for 2 months after stopping treatment. Men using this medication should ask about reliable forms of birth control during treatment and for 6 months after stopping treatment. If you or your partner become pregnant, talk to your doctor right away about the risks and benefits of this medication.It is unknown if this medication passes into breast milk. Because of the possible risk to the infant, breast-feeding is not recommended while using this drug and for 3 months after stopping treatment. Consult your doctor before breast-feeding.

              DRUG INTERACTIONS: Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.Some products that may interact with this drug are: anastrozole, "blood thinners" (e.g., warfarin), estrogens, letrozole, hormonal forms of birth control (e.g., birth control pills, patches, implants), ribociclib.Other medications can affect the removal of tamoxifen from your body, which may affect how tamoxifen works. Examples include butalbital, cimetidine, mitotane, rifamycins (e.g., rifampin), secobarbital, SSRI antidepressants (e.g., fluoxetine, paroxetine), St. John's wort, drugs used to treat seizures (e.g., carbamazepine, phenobarbital, phenytoin, primidone), among others.This medication may interfere with certain laboratory tests (including thyroid tests), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.

              OVERDOSE: If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: shaking, unsteady walking, fainting, or fast/irregular heartbeat.

              NOTES: Do not share this medication with others.Lab and/or medical tests (such as complete blood count, liver function, pelvic exams, mammogram, eye exams) should be done while you are taking this medication. Keep all medical and lab appointments. Consult your doctor for more details.

              MISSED DOSE: If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

              STORAGE: Store at room temperature away from light and moisture. Do not store in the bathroom.If you are using the liquid, do not refrigerate or freeze it. After you open the bottle, discard any unused liquid after 3 months.Keep all medications away from children and pets.Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.

              Information last revised August 2021. Copyright(c) 2021 First Databank, Inc.

              IMPORTANT: HOW TO USE THIS INFORMATION: This is a summary and does NOT have all possible information about this product. This information does not assure that this product is safe, effective, or appropriate for you. This information is not individual medical advice and does not substitute for the advice of your health care professional. Always ask your health care professional for complete information about this product and your specific health needs.

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              Formulary

              FormularyPatient Discounts

              Adding plans allows you to compare formulary status to other drugs in the same class.

              To view formulary information first create a list of plans. Your list will be saved and can be edited at any time.

              Adding plans allows you to:

              • View the formulary and any restrictions for each plan.
              • Manage and view all your plans together – even plans in different states.
              • Compare formulary status to other drugs in the same class.
              • Access your plan list on any device – mobile or desktop.

              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.
              2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
              3 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs.
              4 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
              5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
              6 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
              NC NOT COVERED – Drugs that are not covered by the plan.
              Code Definition
              PA Prior Authorization
              Drugs that require prior authorization. This restriction requires that specific clinical criteria be met prior to the approval of the prescription.
              QL Quantity Limits
              Drugs that have quantity limits associated with each prescription. This restriction typically limits the quantity of the drug that will be covered.
              ST Step Therapy
              Drugs that have step therapy associated with each prescription. This restriction typically requires that certain criteria be met prior to approval for the prescription.
              OR Other Restrictions
              Drugs that have restrictions other than prior authorization, quantity limits, and step therapy associated with each prescription.
              Additional Offers
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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.