The side effects of antithyroid drugs

Antithyroid drugs are a mainstay of therapy of hyperthyroidism, especially when it is due to Graves' disease. Although antithyroid agents are generall y safe, side effects may limit their usefulness in some patients. Side effe cts are classified as minor and major, based on their degree of morbidity. All side effects are more common at higher doses of methimazole (40 mg/day or more), but there is no apparent dose relationship for propylthiouracil ( PTU). The most common minor side effects include cutaneous eruptions, arthr algias, and gastrointestinal upset, which develop in up to 5% of patients a t usual doses. Hair loss, sialadenitis, myopathy, and abnormalities of tast e and smell also have been described. The common major side effects are agr anulocytosis (frequency 0.1-0.4%) and frank polyarthritis. Severe systemic vasculitis or drug-induced lupus (often antineutrophil cytoplasmic antibody positive) are associated with PTU. Hepatic toxicity with methimazole is ch olestatic in nature and not as severe as the potentially life threatening h epatocellular reactions that are seen with PTU. Hypoprothrombinemia and the insulin autoimmune syndrome are exceedingly rare major side effects.