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Methimazole
From WikEM
Contents
Administration
- Type: Antithyroid
- Dosage Forms:
- Routes of Administration: Oral
- Common Trade Names: Tapazole
Adult Dosing
- Thyroid storm: 60 to 80 mg PO daily
- Amiodorone-induced thyrotoxicosis: 40mg PO daily until patient is euthyroid (usually 3-6mo)
- Iodine-induced thyrotoxicosis: 20-40mg PO once
- Hyperthyroidism
- Initial: 10-20mg/day (mild), 30-40mg/day (moderate), 60mg/day (severe) in 1-3 doses
- Maintenance: 5-15mg/day
- 2nd-3rd trimester pregnancy: Use lowest dose needed to keep maternal total T3/T4 slightly above normal range for pregnancy, TSH suppressed, and free T4 at or slightly above upper limit of normal for nonpregnant women
Pediatric Dosing
- Hyperthyroidism:
- Initial: 0.2-0.5 mg/kg PO daily OR 0.4mg/kg PO daily in 3 divided doses
- Maintenance: 50% of initial dose
Special Populations
- Pregnancy Rating: D - see pregnancy dosing
- Lactation risk: Infant risk cannot be ruled out
- Renal dosing: no adjustment
- Hepatic dosing: no adjustment
Contraindications
- Allergy to class/drug
Adverse Reactions
Serious
- Agranulocytosis, aplastic anemia
- Vasculitis
- Pancreatitis
- Hepatotoxicity
Common
- Rash
Pharmacology
- Half-life: 2-28h
- Metabolism: Hepatic
- Excretion: Renal
Mechanism of Action
- Inhibits thyroperoxidase, thus blocking synthesis of thyroid hormones
