Drug information of Methimazole


Treating an overactive thyroid gland and treating or preparing the overactive thyroid gland for surgery. It may also be used when your doctor has advised against the removal of the thyroid. It may also be for other conditions as determined by your doctor.It may also be used for Graves Disease.

Mechanism of effect

Methimazole is an antithyroid agent. It works by inhibiting the production of thyroid hormone . Thyroid hormones are produced and released by the thyroid gland and regulate the body's metabolism.


Methimazole 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


Usual Adult Dose for Hyperthyroidism
Mild hyperthyroidism: 5 mg orally every 8 hours.
Moderately severe hyperthyroidism: 10 mg orally every 8 hours (up to 40 mg per day).
Severe hyperthyroidism: 20 mg orally every 8 hours.
5 to 15 mg orally daily.
Usual Pediatric Dose for Hyperthyroidism
Greater than or equal to 1 year:
Initial dose: 0.4 mg/kg/day orally in 3 equally divided doses 8 hours apart.
Maintenance dose: 0.2 mg/kg/day orally in 3 equally divided doses 8 hours apart.
Maximum dose: 30 mg/day.
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 q6-12 hr for short term, then reduce dosage to maintenance (5-15 mg/day) or reduce frequency to q12hr or q24hr


•Because methimazole may cause hypoprothrombinemia and bleeding, prothrombin time should be evaluated during therapy, especially before surgical procedures.
• Periodic monitoring of thyroid function is necessary, and the finding of an elevated TSH warrants a decrease in dose.
Methimazole may cause drowsiness, dizziness, or lightheadedness. These effects may be worse if you take it with alcohol or certain medicines. Use methimazole with caution. Do not drive or perform other possibly unsafe tasks until you know how you react to it.
• Lab tests, including thyroid and liver function tests, complete blood cell counts, and blood clotting tests (eg, PT, INR), may be performed while you use methimazole. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
Methimazole has been shown to cause harm to the fetus. If you think you may be pregnant, contact your doctor. You will need to discuss the benefits and risks of using methimazole while you are pregnant. Methimazole is found in breast milk. Do not breast-feed while taking methimazole.

Points of recommendation

• Take methimazole by mouth with or without food. If stomach upset occurs, take with food to reduce stomach irritation.
• Take methimazole on a regular schedule around the clock, unless your doctor tells you otherwise.
• If you miss a dose of methimazole , take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.

Pregnancy level


Related drugs

Propyl thiouracil

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