In a pregnant patient with Graves' disease and hyperthyroidism, which antithyroid drug is recommended as first-line treatment?

• A. Propylthiouracil
• B. Methimazole
• C. Carbimazole
• D. Radioiodine

Answer: (A)

In pregnancy, the priority is to control maternal hyperthyroidism while minimizing fetal risk. Propylthiouracil is preferred in the first trimester because methimazole/carbimazole have a higher association with congenital malformations. Propylthiouracil reduces thyroid hormone production and, to some extent, peripheral conversion of T4 to T3, helping keep maternal thyroid levels in check without the greater teratogenic signal seen with methimazole early on. Radioactive iodine is contraindicated during pregnancy. After the first trimester, clinicians may switch to methimazole to reduce maternal risk of liver toxicity from PTU, depending on disease control. So the recommended first-line drug in this scenario is propylthiouracil.