propylthiouracil

Propylthiouracil (PTU) is an antithyroid medication in the thionamide class used to treat hyperthyroidism. It acts by inhibiting thyroid peroxidase, which reduces the synthesis of thyroid hormones (thyroxine, T4, and triiodothyronine, T3). In addition, PTU inhibits the peripheral conversion of T4 to the more active T3 in the liver and other tissues, contributing to a more rapid decrease in circulating thyroid hormone.

PTU is commonly used for Graves’ disease and other forms of hyperthyroidism, as well as in thyrotoxic crisis (thyroid storm) when rapid control of hormone levels is needed. It may be employed as part of preoperative preparation for thyroidectomy or prior to radioactive iodine therapy. In pregnancy, PTU is often preferred during the first trimester due to teratogenic risks associated with methimazole; in the second and third trimesters, methimazole or carbimazole is typically considered, with PTU used if methimazole is unsuitable and with careful monitoring of maternal liver function.

Adverse effects include agranulocytosis, rash, and hepatotoxicity, the latter potentially severe and life-threatening. Other possible effects are arthralgia, lupus-like syndrome, and vasculitis. PTU can interact with other hepatotoxic drugs and may influence anticoagulant therapy; routine monitoring with complete blood counts and liver function tests is advised.

Dosing is oral and given in divided doses, titrated to achieve euthyroidism based on thyroid function tests and clinical response. PTU is generally used for limited periods or as a bridge to other definitive therapies, with a plan to transition when feasible.