Indications and Usage
Methimazole tablets are indicated:
- In patients with Graves’ disease with hyperthyroidism or toxic multinodular goiter for whom surgery or radioactive iodine therapy is not an appropriate treatment option.
- To ameliorate symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy.
Dosage and Administration
Methimazole tablets are administered orally. The total daily dosage is usually given in 3 divided doses at approximately 8-hour intervals.
Adult - The initial daily dosage is 15 mg for mild hyperthyroidism, 30 to 40 mg for moderately severe hyperthyroidism, and 60 mg for severe hyperthyroidism, divided into 3 doses at 8-hour intervals. The maintenance dosage is 5 to 15 mg daily.
Pediatric - Initially, the daily dosage is 0.4 mg/kg of body weight divided into 3 doses and given at 8-hour intervals. The maintenance dosage is approximately ½ of the initial dose.
Contraindications
Methimazole tablets are contraindicated in the presence of hypersensitivity to the drug or any of the other product components.
Adverse Reactions
Major adverse reactions (which occur with much less frequency than the minor adverse reactions) include inhibition of myelopoiesis (agranulocytosis, granulocytopenia, thrombocytopenia, and aplastic anemia), drug fever, a lupus-like syndrome, insulin autoimmune syndrome (which can result in hypoglycemic coma), hepatitis (jaundice may persist for several weeks after discontinuation of the drug), periarteritis, and hypoprothrombinemia. Nephritis occurs very rarely. There have been postmarketing case reports of acute pancreatitis.
There are reports of a vasculitis, often associated with the presence of anti-neutrophilic cytoplasmic antibodies (ANCA), resulting in severe complications [see WARNINGS].
Minor adverse reactions include skin rash, urticaria, nausea, vomiting, epigastric distress, arthralgia, paresthesia, loss of taste, abnormal loss of hair, myalgia, headache, pruritus, drowsiness, neuritis, edema, vertigo, skin pigmentation, jaundice, sialadenopathy, and lymphadenopathy.
To report SUSPECTED ADVERSE REACTIONS, contact AiPing Pharmaceutical, Inc. at 1-844-374-0016 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.
Drug Interactions
Anticoagulants (oral):
Due to potential inhibition of vitamin K activity by methimazole, the activity of oral anticoagulants (e.g., warfarin) may be increased; additional monitoring of PT/INR should be considered, especially before surgical procedures.
ß-adrenergic blocking agents:
Hyperthyroidism may cause an increased clearance of beta blockers with a high extraction ratio. A dose reduction of beta-adrenergic blockers may be needed when a hyperthyroid patient becomes euthyroid.
Digitalis glycosides:
Serum digitalis levels may be increased when hyperthyroid patients on a stable digitalis glycoside regimen become euthyroid; a reduced dosage of digitalis glycosides may be needed.
Theophylline:
Theophylline clearance may decrease when hyperthyroid patients on a stable theophylline regimen become euthyroid; a reduced dose of theophylline may be needed.
Overdosage
Signs and Symptoms
Symptoms may include nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, and edema. Aplastic anemia (pancytopenia) or agranulocytosis may be manifested in hours to days. Less frequent events are hepatitis, nephrotic syndrome, exfoliative dermatitis, neuropathies, and CNS stimulation or depression. No information is available on the median lethal dose of the drug or the concentration of methimazole in biologic fluids associated with toxicity and/or death.
Treatment
To obtain up-to-date information about the treatment of overdose, a good resource is your certified Regional Poison Control Center. In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in the patient.
In the event of an overdose, appropriate supportive treatment should be initiated as dictated by the patient’s medical status.
Description
Methimazole, USP (1-methylimidazole-2-thiol) is a white, crystalline substance that is freely soluble in water. It differs chemically from the drugs of the thiouracil series primarily because it has a 5- instead of a 6-membered ring.
Methimazole tablet, USP contains 5 or 10 mg methimazole, an orally administered antithyroid drug.
Each tablet also contains lactose monohydrate, magnesium stearate, potato starch and talc.
The molecular weight is 114.17, and the molecular formula is C4H6N2S. The structural formula is as follows:
Methimazole-Structural FormulaClinical Pharmacology
Methimazole inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism. The drug does not inactivate existing thyroxine and triiodothyronine that are stored in the thyroid or circulating in the blood nor does it interfere with the effectiveness of thyroid hormones given by mouth or by injection.
Methimazole is readily absorbed in the gastrointestinal tract, metabolized in the liver, and excreted in the urine.
How Supplied / Storage and Handling
Methimazole Tablets USP, 5 mg are supplied as white, round, flat-faced, beveled-edged tablets with “VM” on one side and scored on the other.
They are available in:
Bottles of 100, NDC 11788-011-01
Methimazole Tablets USP, 10 mg are supplied as white, round, flat-faced, beveled-edged tablets with “XM” on one side and scored on the other.
They are available in:
Bottles of 100, NDC 11788-012-01
Store at 20° to 25°C (68° to 77°F) [See USP Controlled Room Temperature].
Dispense in a tight, light-resistant container.
Manufactured for:
AiPing Pharmaceutical, Inc.
Hauppauge, NY 11788
LB1636
Revised: 01/2026
Patient Counseling Information
Patients should be advised that if they become pregnant or intend to become pregnant while taking an antithyroid drug, they should contact their physician immediately about their therapy.
Inform patients that cases of vasculitis resulting in severe complications have occurred with methimazole tablets. Inform patients to promptly report symptoms that may be associated with vasculitis including new rash, hematuria or decreased urine output, dyspnea or hemoptysis [see WARNINGS and ADVERSE REACTIONS].