Antithyroid Drugs

Abstract

Antithyroid medications, carbimazole (CBZ) and its active metabolite methimazole (MMI), and propylthiouracil (PTU) inhibit the synthesis of the thyroid hormones tetraiodothyronine (T4) and triiodothyronine (T3). Antithyroid drug treatment is mainly used to restore the euthyroid state in hyperthyroid Graves’ disease. The usual treatment strategy is a 12–18month long cure with subsequent remission in 40% of the patients. Antithyroid drug treatment is mandatory in the preparation to thyroidectomy and should be considered before treatment with radioactive iodine, the two radical/ablative strategy possibly elected after relapse of the disease. Incidence of the adverse effects of the antithyroid drugs is 4%–5% for the minor (urticaria, myalgia, arthralgia) but much lower, 0.1%–0.7%, for the severe ones (agranulocytosis, hepatitis with the risk of liver failure, anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis). PTU, because of the risk of uncommon but very severe liver failure, should no longer be the first-line antithyroid drug. During pregnancy, management of antithyroid drug treatment must be adapted to the specific evolution of Graves’ disease and prevent the risk of fetal hypothyroidism. Antithyroid drug treatment does not contraindicate breast-feeding.