A 26-year-old woman with Graves' disease is 8 weeks pregnant. Which of the following antithyroid drug regimens is most appropriate during the FIRST trimester?
- A Methimazole throughout pregnancy
- B Propylthiouracil (PTU) during first trimester, then switch to methimazole ✓
- C Radioactive iodine I-131 to definitively treat Graves' disease
- D Carbimazole throughout pregnancy
Correct answer: B. Propylthiouracil (PTU) during first trimester, then switch to methimazole
Explanation
PTU is preferred in the first trimester because methimazole is associated with embryopathy (choanal atresia, aplasia cutis, esophageal atresia). After the first trimester (when organogenesis is complete), PTU carries a risk of serious hepatotoxicity, so switching to methimazole is recommended. Radioactive iodine is absolutely contraindicated in pregnancy. Carbimazole is a prodrug of methimazole and carries the same teratogenic risk in the first trimester.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.