Drug reference

Methimazole

Antithyroid · Anti-thyroid drug

Also known as MMI

AntithyroidAnti-thyroid drug

CDSCO approvedSchedule H

EXCRETION

—

not curated

INTERACTIONS

8 major

SEVERE in our sources

PREGNANCY

FDA category + note

Top interactionssee all 8 →

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Mechanism

Methimazole, a thionamide, directly interferes with the synthesis of thyroid hormones. It inhibits the thyroid peroxidase (TPO) enzyme, which is responsible for the iodination of thyroglobulin. Additionally, it inhibits the coupling reaction where iodotyrosines are combined to form thyroxine (T4) and triiodothyronine (T3).

Indications

Control of hyperthyroid stateshyperthyroidismGraves disease (drug of choice)Thyrotoxicosis (Graves’ disease, toxic nodular goiter)

Dosing

Adult: its antithyroid effects. Methimazole and Propylthiouracil: 50–150 mg TDS followed by 25–50 mg. BD–TDS for maintenance. PTU 50 mg tab.. Methimazole: 5–10 mg TDS initially, maintenance dose. 5–15 mg daily in 1–2 divided doses.. Carbimazole: 5–15 mg TDS initially, maintenance dose

Pharmacokinetics

Half-life

~4–6 h (plasma), long intrathyroidal t1/2

Protein binding

Nil

Metabolism

Decreased in severe liver disease, normal in severe kidney disease.

Excretion

Drugs and metabolites appear largely in the urine.

Contraindications

first trimester of pregnancy due to methimazole-associated embryopathy

Side effects

Common

mild urticarial papular rashpain and stiffness in the jointsparesthesiasheadachenauseaskin pigmentationloss of hairg.i. intoleranceskin rashesjoint painhypothyroidism (due to overtreatment)goiter (due to overtreatment)

Serious