For the treatment of hyperthyroidism, goiter, Graves disease and psoriasis.
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.
Oral LD<sub>50</sub> 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.
Rapid with an oral bioavailability of 93%.
5-6 hours
Methimazole is excreted in the urine.