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methimazole (Rx)Brand and Other Names:Northyx, Tapazole

 
 
 

Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

tablet

  • 5mg
  • 10mg
more...

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: 5-15 mg/day PO divided q8hr

Graves Disease

10-20 mg/day PO; after euthyroidism is achieved, reduce dosage by 50% and administer for 12-18 months

Thyrotoxic Crisis

20-30 mg q6-12hr for short term, then reduce dosage to maintenance (5-15 mg/day) or reduce frequency to q12hr or q24hr

Dosage Forms & Strengths

tablet

  • 5mg
  • 10mg
more...

Hyperthyroidism

Initial: 0.4-0.7 mg/kg/day PO divided q8hr 

Maintenance: 1/3-2/3 of initial PO dosage divided q8hr PO

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  

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Interactions

Interaction Checker

methimazole and

No Results

     
     activity indicator 
    No Interactions Found
    Interactions Found

    Contraindicated

      Serious - Use Alternative

        Significant - Monitor Closely

          Minor

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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

            Liver disease

            Hepatic reactions may occur

            Pregnancy

            Lupuslike syndrome reported

            Antineutrophil cytoplasmic autoantibody (ANCA)-positive vasculitis reported

            Dosage >40 mg/day

            Patient age >40 years

            Concurrent administration of other agranulocytosis-causing drugs

            Risk of rare but serious agranulocytosis, cholestastic jaundice, and rare congenital abnormalities (propylthiouracil [PTU] preferred in pregnancy)

            Prolonged treatment may cause hypothyroidism

            Discontinue if agranulocytosis, pancytopenia, hepatitis, fever, or exfoliative dermatitis occurs

            10 times more potent than PTU, but action may be less consistent

            High rate of relapse (more likely in smokers)

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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.

            more...
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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

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            Formulary

            FormularyPatient Discounts

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

            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            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.
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