Methimazol

Methimazole is an antithyroid medication in the thionamide class used to treat hyperthyroidism. It works by inhibiting thyroid peroxidase, the enzyme that catalyzes iodination of tyrosine residues and the coupling of iodotyrosines in thyroglobulin. By blocking these steps, methimazole reduces the synthesis of thyroid hormones T4 and T3. It has little effect on the peripheral conversion of T4 to T3, a distinction from some other thionamides.

Common indications include Graves’ disease, toxic multinodular goiter, and solitary toxic nodules. It is often used to achieve euthyroidism before thyroidectomy or before radioactive iodine therapy, or as long‑term therapy when surgery is not desired.

Administration and dosing: methimazole is given orally, with or without food. Dosing is individualized; typical adult regimens range from 5 to 30 mg daily, sometimes divided into two doses, with adjustments based on serial thyroid function tests (initially every 4 weeks).

Monitoring and safety: routine monitoring of thyroid function and complete blood counts is recommended. Serious adverse effects include agranulocytosis and hepatotoxicity; patients should report fever or sore throat promptly. Methimazole is teratogenic and crosses the placenta, so use in pregnancy requires careful risk–benefit assessment; in the first trimester propylthiouracil is often preferred, with methimazole used later in pregnancy if needed. Caution is advised during breastfeeding.

Availability and alternatives: methimazole is marketed under various brand names in different countries (for example Tapazole in the United States). Other antithyroid agents include propylthiouracil and carbimazole, as well as radioactive iodine therapy or surgery for definitive treatment.