Drug information of Methimazole

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.

Pharmacodynamic

Methimazole Inhibits synthesis of thyroid hormone by blocking oxidation of iodine in thyroid gland ; blocks synthesis of thyroxine (T4) and triiodothyronine (T3)

Pharmacokinetics

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

Dosage

Usual Adult Dose for Hyperthyroidism
Initial:
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.
Maintenance:
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

Drug contraindications

Lactation , allergic to any ingredient in methimazole

Side effects

nausea , Headache , dizziness , vomiting , asthenia , fever , Tremor , hemorrhage , itching , difficulty urinating , skin rush , tiredness , yellowing of the skin , yellowing of the eyes , joint or muscle pain , shortness of breath , Change in taste , lightheadedness , numbness and tingling , stomach upset , Severe allergic reactions , swelling of the face , swelling of the tongue , tightness in the chest , dark urine , fast or irregular heartbeat , fainting , persistent sore throat , severe or persistent headache , stomach pain , vision chang

Interactions

Alprazolam , Esomeprazole , Acetaminophen , Omega 3 , Pregabalin , Duloxetine , Clopidogrel , Calcium / vitamin d , Aspirin , Zolpidem , Furosemide , Lorazepam , Metoprolol , Vitamin C , Vitamin D3 , Remdesivir

Alerts

•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.
• PREGNANCY and BREAST-FEEDING:
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

D

Related drugs

Propyl thiouracil