A 32-year-old woman with Graves' disease presents with thyrotoxicosis and a heart rate of 110 bpm. She is planning pregnancy within 6 months. Which is the drug of choice for her management?

Explanation

## Drug of Choice in Hyperthyroidism: Pregnancy Planning Context **Key Point:** Propylthiouracil (PTU) is the preferred antithyroid agent in women planning pregnancy or in the first trimester of pregnancy due to a lower teratogenic risk compared to methimazole. ### Why PTU is Preferred in Pregnancy **High-Yield:** Methimazole is associated with a rare embryopathy (methimazole embryopathy) characterized by: - Esophageal atresia - Choanal atresia - Cutis aplasia - Developmental delay PTU carries a much lower risk of congenital anomalies and is therefore the drug of choice for women in the reproductive age group planning pregnancy or already pregnant. ### Comparison of Antithyroid Drugs | Feature | PTU | Methimazole | |---------|-----|-------------| | **Mechanism** | Inhibits TPO; blocks peripheral conversion of T₄ to T₃ | Inhibits TPO only | | **Onset of action** | Faster (due to dual action) | Slower | | **Half-life** | 1–2 hours | 4–6 hours | | **Dosing frequency** | 3× daily | 1–2× daily | | **Teratogenicity** | Low risk (PTU of choice) | Methimazole embryopathy | | **Hepatotoxicity** | Severe (rare but serious) | Mild | | **Agranulocytosis** | 0.2–0.5% | 0.3–0.5% | | **Use in pregnancy** | First trimester preferred | Avoid first trimester | **Clinical Pearl:** PTU's additional benefit of blocking peripheral T₄ → T₃ conversion makes it faster-acting, which is advantageous in symptomatic thyrotoxicosis, though the pregnancy indication is the primary reason here. ### Role of Other Options - **Propranolol:** β-blocker used for symptom control (tachycardia, tremor, anxiety) but does NOT treat the underlying thyroid disease. It may be used adjunctively but is not the primary antithyroid agent. - **Methimazole:** Effective but teratogenic; reserved for non-pregnant women or second/third trimester after PTU induction. - **Iodine solution (Lugol's):** Used only acutely in thyroid storm or preoperatively to reduce gland vascularity; not suitable for chronic management. **Mnemonic:** **PTU in Pregnancy** — PTU is the agent of choice when **P**regnancy is **P**lanned or **P**resent.