Propylthiouracil (PTU) is preferred over carbimazole in which of the following clinical situations?

• A Long-term maintenance therapy of Graves disease
• B Paediatric hyperthyroidism
• C Post-radioiodine ablation maintenance
• D Thyroid storm in the first trimester of pregnancy ✓

Explanation

PTU is preferred in thyroid storm and in the first trimester of pregnancy because it additionally blocks peripheral conversion of T4 to the more active T3 by inhibiting type 1 deiodinase — an effect not shared by carbimazole. In thyroid storm, rapidly reducing T3 levels is critical. In the first trimester, carbimazole/methimazole carries a specific risk of aplasia cutis and choanal/oesophageal atresia (embryopathy); PTU's teratogenic risk is lower in this window.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.