This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Which antithyroid drug can be safely used in pregnancy \nSelect and explain. \nA. Propylthiouracil, B. I121, C. Methimazole, D. Carbimazole', 'role': 'user'}, {'content': 'Answer: A \nExplanation: This question has been repeated several times before.\xa0Remember these important points. \nAll antithyroid drugs can cross placenta so risk of fetal hypothyroidism and\xa0goitre is always there. Both carbimazole and propylthiouracil can be used during pregnancy,\xa0but propylthiouracil is the drug of choice because its greater protein binding allows low doses of propylthiouracil to be transferred\xa0across the placenta and therefore less chance of hypothyroidism. \nThe lowest effective dose of propylthiouracil should be given and it is often possible\xa0to stop treatment in the last trimester since TSH Receptor antibodies tend to decline in pregnancy.\nRadioactive iodine is C/I during pregnancy. It can destroy the fetal thyroid tissue resulting in cretinism Carbimazole and methimazole have been associated with rare cases of foetal aplasia cutis.', 'role': 'assistant'}]