one of a group of antithyroid drugs prescribed in the treatment of hyperthyroidism. Thioamide drugs act by inhibiting the synthesis of thyroid hormone. The principal thioamides are propylthiouracil, methimazole, methylthiouracil, and carbimazole; propylthiouracil and methimazole are the only members of this group still available. Adverse reactions include agranulocytosis, hypersensitivity, and a mild transient pruritus. Because agranulocytosis may occur very rapidly, serial white blood cell counts are not useful in diagnosing that complication of treatment. Instead, the patient is requested to report immediately instances of sore throat and fever, which often herald the onset of agranulocytosis. Prompt discontinuation of the drug before serious depletion of granulocytic white blood cells develops usually results in complete recovery. Use of antithyroid medications in pregnancy may result in fetal hypothyroidism, goiter, and cretinism.