Hyperthyroidism

Methimazole, a thyroid hormone synthesis inhibitor, is used in the treatment of hyperthyroidism. Its actions are similar to propylthiouracil although it does not inactivate the existing thyroxine and triiodothyronine stored in the thyroid or in the blood.

Absorption:
Oral: readily absorbed
Metabolism:
rapidly metabolized :
Excretion:
Renal

Hypersensitivity to methimazole or any component of the product

D (FDA)

WHO documentation states insufficient data.
Infant risk cannot be ruled out.(MDX)

Common:
Dermatologic: Rash
Serious:
Cardiovascular: Vasculitis
Gastrointestinal: Pancreatitis
Hematologic: Agranulocytosis (0.3% to 1% ), Aplastic anemia
Hepatic: Hepatotoxicity

Hyperthyroidism:
Initial, 10 to 20 mg ORALLY once daily; maintenance, OR mild, 15 mg/day; moderate, 30 to 40 mg/day; severe, 60 mg/day; given in 3 divided doses 8 hours apart
Maintenance, 5 to 10 mg ORALLY once daily OR 5 to 15 mg ORALLY per day
Duration: Taper or discontinue if thyroid stimulating hormone levels are normal after 12 to 18 months in patients using methimazole as primary therapy for Grave disease
Pregnancy - Thyrotoxicosis due to Graves' disease:
(Second and third trimesters) Use lowest dose to keep mother's total thyroxine (T4) and triiodothyronine (T3) levels slightly above normal range for pregnancy, keep TSH suppressed, and keep free T4 at or slightly above ULN for nonpregnant women; assess monthly and adjust dose as required
Thyroid storm:
60 to 80 mg/day ORALLY
Thyrotoxicosis, Drug-induced:
(Amiodarone-induced, type 1) 40 mg ORALLY once daily until patient is euthyroid, generally about 3 to 6 months; if continued high-dose therapy is required, dose may be divided
(Iodine-induced) 20 to 40 mg ORALLY as a single or divided dose.

Hyperthyroidism:
Initial, 0.2 to 0.5 mg/kg ORALLY once daily is typical with a range of 0.1 to 1 mg/kg/day; give for 1 to 2 years then assess for remission OR 0.4 mg/kg/day ORALLY in 3 divided doses 8 hours apart .
Alternatively, using tablet measurement, (infant), 1.25 mg/day; (aged 1 to 5 years), 2.5 to 5 mg/day; (aged 5 to 10 years), 5 to 10 mg/day; (aged 10 to 18 years), 10 to 20 mg/day
Maintenance, 50% of the initial dose .