system
Medical AI Inquiry: You were designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.
user
Which of the following is the agent of choice for treating thyrotoxicosis during pregnancy ?
assistant
The correct answer is  The antithyroid drugs like carbimazole, methimazole crosses the placenta (transplacental passage) and produce fetal hypothyroidism and goiter if the maternal dose is excessive. However, propylthiouracil should be used in early gestation at low doses as its greater protein binding allows less transfer to the foetus. Carbimazole and methimazole are also associated with rare cases of fetal aplasia cutis and other defects, such as choanal atresia. Pregnancy and breast-feeding are absolute contraindications to radioiodine treatment I131. Reference : page 254 Essentials of Medical Pharmacology K D Tripathi 7th edition and page 2297 Harrison's Principles of Internal Medicine 19th edition