Active ingredient: Methimazole - Brands, Medical Use, Clinical Data

Brands, Medical Use, Clinical Data

Drug Category

• Antithyroid Agents

Dosage Forms

• Tablet (5 or 10 mg)

Brands / Synonyms

Basolan; Danantizol; Favistan; Frentirox; Mercaptazole; Mercasolyl; Mercazole; Mercazolyl; Merkastan; Merkazolil; Metazolo; Methamazole; Methiamazole; Methimazol; Methimazole; Methylmercaptoimidazole; Metizol; Metothyrin; Metothyrine; Metotirin; Propyl-Thyracil; Strumazol; Strumazole; Tapazole; Tapuzole; Thacapzol; Thiamazol; Thiamazole; Thimazole; Thycapsol; Thycapzol; Thymidazol; Thymidazole; USAF EL-30

Indications

For the treatment of hyperthyroidism, goiter, Graves disease and psoriasis.

Pharmacology

Used in the treatment of hyperthyroidism or an overactive thyroid gland, methimazole inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism. It may also be used to ameliorate hyperthyroidism in preparation for subtotal thyroidectomy or radioactive iodine therapy.

Mechanism of Action

Methimazole binds to thyroid peroxidase and thereby inhibits the conversion of iodide to iodine. Thyroid peroxidase normally converts iodide to iodine (via hydrogen peroxide as a cofactor) and also catalyzes the incorporation of the resulting iodide molecule onto both the 3 and/or 5 positions of the phenol rings of tyrosines found in thyroglobulin. Thyroglobulin is degraded to produce thyroxine (T4) and tri-iodothyronine (T3), which are the main hormones produced by the thyroid gland. So methimazole effectively inhibits the production of new thyroid hormones.

Absorption

Rapid with an oral bioavailability of 93%.

Toxicity

Oral LD₅₀ in rats is 2250 mg/kg. Symptoms of overdose include nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, and edema. Aplastic anemia (pancy-topenia) or agranulocytosis may be manifested in hours to days. Less frequent events are hepatitis, nephrotic syndrome, exfoliative dermatitis, neuropathies, and CNS stimulation or depression.

Biotrnasformation / Drug Metabolism

Primarily hepatic. Metabolized rapidly, requiring frequent administration.

Contraindications

Tapazole is contraindicated in the presence of hypersensitivity to the drug and in nursing mothers because the drug is excreted in milk.

Drug Interactions

Anticoagulants (oral): The activity of oral anticoagulants may be potentiated by anti-vitamin-K activity attributed to methimazole.

ß-adrenergic blocking agents: Hyperthyroidism may cause an increased clearance of beta 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; reduced dosage of digitalis glycosides may be required.

Theophylline: Theophylline clearance may decrease when hyperthyroid patients on a stable theophylline regimen become euthyroid; a reduced dose of theophylline may be needed.