Methimazole

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Administration

  • Type: Antithyroid
  • Dosage Forms: Tablet; 5mg, 10mg
  • 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

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

Comments

See Also

References