methimazole (Rx)

Brand and Other Names:Northyx, Tapazole
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Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

tablet

  • 5mg
  • 10mg

Hyperthyroidism

Mild: 15 mg/day PO divided q8hr initially

Moderate: 30-40 mg/day PO divided q8hr initially

Severe: 60 mg/day PO divided q8hr initially

Maintenance: 5-30 mg/day PO divided q8hr

Graves Disease

10-20 mg/day PO once; after euthyroidism is achieved, reduce dosage by 50% and administer for 12-18 months; may subsequently taper or discontinue if TSH levels are normal

Thyrotoxicosis (Off-label)

15-20 mg PO q4hr during first day as adjunct to other agents; reduce frequency to qDay or q12hr once patient is stable

Orphan Designations

Brain metastases: Orphan designation (plus liothyronine) for brain metastases in patients with primary lung cancer

Glioblastoma mutiforme: Orphan designation (plus liothyronine) for treatment of glioblastoma multiforme

Sponsor

  • Musli Thyropeutics Ltd; 6 Hagefen Street, P. O. Box 529; Zur Moshe, Israel

Dosage Forms & Strengths

tablet

  • 5mg
  • 10mg

Hyperthyroidism

Initial: 0.5-0.7 mg/kg/day PO qDay or divided q8hr  

Maintenance: 0.2 mg/kg/day PO qDay or divided q8hr

Not to exceed 30 mg/day

Graves Disease

0.2-0.5 mg/kg/day PO; after euthyroidism is achieved, reduce dosage by 50% and administer for 1-2 years  

Thyrotoxicosis (Off-label)

0.5-1 mg/kg/day PO divided q8hr; adjust subsequent doses and duration of treatment based on patient response

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Interactions

Interaction Checker

and methimazole

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    Interactions Found

    Contraindicated

      Serious - Use Alternative

        Significant - Monitor Closely

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            Contraindicated (2)

            • eliglustat

              methimazole 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.

            • sodium iodide I-131

              methimazole will decrease the level or effect of sodium iodide I-131 by Other (see comment). Contraindicated. Discontinue antithyroid medications at least 3-4 days before administering sodium iodide I-131 and do not coadminister; thyroid agents decrease update of sodium iodide I-131 by the thyroid gland

            Serious - Use Alternative (5)

            • carbamazepine

              methimazole, carbamazepine. Either increases toxicity of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Increased risk of agranulocytosis.

            • clozapine

              methimazole, clozapine. Either increases toxicity of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Increased risk of agranulocytosis.

            • fedratinib

              methimazole will increase the level or effect of fedratinib by Other (see comment). Avoid or Use Alternate Drug. Avoid coadministration of fedratinib (a CYP3A4 and CYP2C19 substrate) with dual CYP3A4 and CYP2C19 inhibitor. Effect of coadministration of a dual CYP3A4 and CYP2C19 inhibitor with fedratinib has not been studied.

            • lonafarnib

              methimazole 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.

            • propylthiouracil

              propylthiouracil, methimazole. Either increases toxicity of the other by pharmacodynamic synergism. Avoid or Use Alternate Drug. Increased risk of agranulocytosis.

            Monitor Closely (30)

            • antithrombin alfa

              methimazole decreases effects of antithrombin alfa by pharmacodynamic antagonism. Use Caution/Monitor.

            • antithrombin III

              methimazole decreases effects of antithrombin III by pharmacodynamic antagonism. Use Caution/Monitor.

            • argatroban

              methimazole decreases effects of argatroban by pharmacodynamic antagonism. Use Caution/Monitor.

            • atogepant

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

            • avapritinib

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

            • axitinib

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

            • bemiparin

              methimazole decreases effects of bemiparin by pharmacodynamic antagonism. Use Caution/Monitor.

            • bivalirudin

              methimazole decreases effects of bivalirudin by pharmacodynamic antagonism. Use Caution/Monitor.

            • brexpiprazole

              methimazole will increase the level or effect of brexpiprazole by affecting hepatic enzyme CYP2D6 metabolism. Modify Therapy/Monitor Closely. Administer a quarter of brexpiprazole dose if coadministered with a moderate CYP2D6 inhibitor PLUS a strong/moderate CYP3A4 inhibitor.

            • dalteparin

              methimazole decreases effects of dalteparin by pharmacodynamic antagonism. Use Caution/Monitor.

            • enoxaparin

              methimazole decreases effects of enoxaparin by pharmacodynamic antagonism. Use Caution/Monitor.

            • finerenone

              methimazole 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

              methimazole 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.

            • fondaparinux

              methimazole decreases effects of fondaparinux by pharmacodynamic antagonism. Use Caution/Monitor.

            • heparin

              methimazole decreases effects of heparin by pharmacodynamic antagonism. Use Caution/Monitor.

            • isavuconazonium sulfate

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

            • ivacaftor

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

            • lemborexant

              methimazole 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.

            • lomitapide

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

            • lycopus

              lycopus increases effects of methimazole by pharmacodynamic synergism. Use Caution/Monitor. Lycopus blocks peripheral conversion of T4 to T3.

            • midazolam intranasal

              methimazole 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.

            • oliceridine

              methimazole 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.

            • phenindione

              methimazole decreases effects of phenindione by pharmacodynamic antagonism. Use Caution/Monitor.

            • potassium iodide

              potassium iodide, methimazole. Mechanism: pharmacodynamic synergism. Use Caution/Monitor. Concomitant use with antithyroid drugs may potentiate the hypothyroid and goitrogenic effects of potassium iodide.

            • protamine

              methimazole decreases effects of protamine by pharmacodynamic antagonism. Use Caution/Monitor.

            • tamsulosin

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

            • tazemetostat

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

            • theophylline

              methimazole increases levels of theophylline by decreasing elimination. Use Caution/Monitor.

            • tinidazole

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

            • warfarin

              methimazole decreases effects of warfarin by pharmacodynamic antagonism. Use Caution/Monitor.

            Minor (4)

            • cadexomer iodine

              cadexomer iodine, methimazole. Mechanism: pharmacodynamic synergism. Minor/Significance Unknown. Additive hypothyroid effects.

            • iodinated glycerol

              iodinated glycerol, methimazole. Mechanism: pharmacodynamic synergism. Minor/Significance Unknown. Additive hypothyroid effects.

            • iodine

              iodine, methimazole. Mechanism: pharmacodynamic synergism. Minor/Significance Unknown. Additive hypothyroid effects.

            • ruxolitinib

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

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            Adverse Effects

            Frequency Not Defined

            Agranulocytosis

            Alopecia

            Aplastic anemia

            Dermatologic reactions (eg, rash, pruritus, skin pigmentation)

            Hepatotoxicity

            Leukocytoclastic vasculitis

            Neuritis

            Polyarthritis

            Pruritus

            Salivary gland swelling

            Skin pigmentation

            Thrombocytopenia

            Urticaria

            Vertigo

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            Warnings

            Contraindications

            Hypersensitivity

            Breastfeeding

            Cautions

            Lupus-like syndrome reported

            Hypoprothrombinemia and bleeding may occur; monitor, especially before surgical procedure performed

            Antineutrophil cytoplasmic autoantibody (ANCA)-positive vasculitis reported; discontinue use in presence of vasculitis

            Concurrent administration of other agranulocytosis-causing drugs

            Prolonged treatment may cause hypothyroidism; routinely monitor free T4 levels and TSH; adjust dose as necessary to maintain euthyroid state

            Significant bone marrow suppression may occur; use caution if administered with other agents known to cause myelosupression; discontinue if significan agranulocytosis, leukopenia, or aplastic anemia occurs

            Hepatitis reported; discontinue if it occurs or if clinically significant hepatic enzyme levels, including transaminases >3 times upper limit of normal observed

            Discontinue if unexplained fever occurs

            Antithyroid agents associated with rare but severe dermatologic reactions; discontinue if exfoliative dermatitis occurs

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            Pregnancy & Lactation

            Pregnancy category: D (drug crosses placenta)

            Lactation: Drug distributed in breast milk; use contraindicated by manufacturer (American Academy of Pediatrics [AAP] Committee states that drug is compatible with nursing; American Academy of Family Physicians [AAFP] states that it is safe for nursing)

            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

            Inhibits synthesis of thyroid hormone by blocking oxidation of iodine in thyroid gland; blocks synthesis of thyroxine (T4) and triiodothyronine (T3)

            Absorption

            Bioavailability: 80-95%

            Onset: PO, 12-18 hr

            Duration: 36-72 hr

            Peak plasma time: 1-2 hr

            Distribution

            Protein bound: None

            Metabolism

            Metabolized by liver

            Elimination

            Half-life: 4-6 hr

            Excretion: Urine

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            Images

            BRAND FORM. UNIT PRICE PILL IMAGE
            Tapazole oral
            -
            10 mg tablet
            Tapazole oral
            -
            5 mg tablet
            methimazole oral
            -
            10 mg tablet
            methimazole oral
            -
            10 mg tablet
            methimazole oral
            -
            5 mg tablet
            methimazole oral
            -
            10 mg tablet
            methimazole oral
            -
            5 mg tablet
            methimazole oral
            -
            10 mg tablet
            methimazole oral
            -
            10 mg tablet
            methimazole oral
            -
            10 mg tablet
            methimazole oral
            -
            5 mg tablet
            methimazole oral
            -
            5 mg tablet

            Copyright © 2010 First DataBank, Inc.

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            Patient Handout

            Patient Education
            methimazole oral

            METHIMAZOLE - ORAL

            (meh-THIM-uh-zole)

            COMMON BRAND NAME(S): Tapazole

            USES: Methimazole is used to treat overactive thyroid (hyperthyroidism). It works by stopping the thyroid gland from making too much thyroid hormone.

            HOW TO USE: Take this medication by mouth with or without food as directed by your doctor, usually 1 to 3 times a day.Dosage is based on your medical condition and response to treatment. For children, the dosage is also based on their weight.Take this medication exactly as directed. Do not increase your dose or take it more often than prescribed. Your condition will not improve faster, and your risk of side effects will increase.Use this medication regularly to get the most benefit from it. To help you remember, take it at the same time(s) each day. Do not stop taking this medication without consulting your doctor.Tell your doctor if your condition does not improve or if it worsens.

            SIDE EFFECTS: Stomach upset, nausea, vomiting, or mild rash/itching may occur. If any of these effects last or get worse, tell your doctor or pharmacist 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: joint/muscle pain, numb/tingling skin, shortness of breath, coughing up blood, signs of liver problems (such as nausea/vomiting that doesn't stop, yellowing eyes/skin, dark urine, severe stomach/abdominal pain), signs of kidney problems (such as change in the amount of urine, bloody urine).This medication may rarely cause very serious blood disorders (such as a low number of red cells, white cells, and platelets), especially during the first few months of treatment. Tell your doctor right away if you develop any of the following symptoms: signs of infection (such as fever, persistent sore throat), easy bruising/bleeding, unusual tiredness.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 methimazole, 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 disorders (such as agranulocytosis, thrombocytopenia), liver disease, pancreatitis.Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).This medication is not recommended for use during the first 3 months of pregnancy. Your doctor may direct you to use another medication during that time. It should be used only when clearly needed during the last 6 months of pregnancy. Discuss the risks and benefits with your doctor. If you are planning pregnancy, become pregnant, or think you may be pregnant, contact your doctor right away.This medication passes into breast milk. 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 include: "blood thinners" (such as warfarin), digoxin.

            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.

            NOTES: Do not share this medication with others.Laboratory and/or medical tests (such as complete blood counts, liver/thyroid function tests, prothrombin time) should be performed periodically to monitor your progress or check for side effects. 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. Storage temperature ranges differ according to different manufacturers, so consult your pharmacist for more information. Do not store in the bathroom. 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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            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.