metimazol

Metimazol, also known as methimazole, is an antithyroid medication in the thionamide class. It inhibits thyroid peroxidase, the enzyme responsible for the iodination of tyrosine residues and the coupling of iodotyrosines, thereby reducing the synthesis of the thyroid hormones triiodothyronine (T3) and thyroxine (T4). The drug does not affect the release of existing hormone.

Indications include hyperthyroidism due to Graves disease, toxic multinodular goiter, and toxic adenoma. It is commonly used to control hyperthyroidism before thyroidectomy or radioactive iodine therapy and to manage thyrotoxic crises in selected patients when rapid control is required, though propylthiouracil is preferred in thyroid storm.

Adult dosing typically ranges from 5 to 30 mg per day, given once daily or in divided doses, with adjustments based on clinical response and thyroid function tests. Lower starting doses are used for mild disease or in children; higher doses may be necessary for severe disease. Dosing in pregnancy and children should be carefully tailored by a clinician.

Methimazole is rapidly absorbed after oral intake and reaches peak blood levels within one to two hours. It has a relatively short plasma half-life of about four to six hours and is largely excreted by the kidneys after hepatic metabolism.

Adverse effects range from mild rash and pruritus to more serious events such as agranulocytosis and hepatotoxicity. Patients should be instructed to report fever, sore throat, or signs of infection promptly. Regular monitoring of thyroid function, as well as complete blood counts and liver tests, is recommended during treatment. In pregnancy, methimazole is associated with teratogenic risks in the first trimester; thus, guidelines typically favor propylthiouracil during the first trimester and switch to methimazole in the second trimester. Methimazole is excreted in breast milk and should be used in lactating women only when the potential benefit justifies the potential risk.