Antithyroid drugs are the treatment of choice for hyperthyroidism during pregnancy (18). They inhibit thyroid hormone synthesis by reducing iodine organification and coupling of MIT and DIT. Methimazole (MMI), propylthiouracil (PTU), and carbimazole have been used for the treatment of hyperthyroidism during pregnancy. The pharmacokinetics of MMI is not altered in pregnancy; it has been reported that serum PTU concentrations may be lower in the third than in the first and second trimesters of gestation (19). Use of PTU should be restricted to first trimester of pregnancy, after which change to MMI is recommended