This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti Thyroid, Subject name: Pharmacology
Conversion of T4 to T3 is inhibited by all except: 
Select and explain. 
A. Propranolol, B. Propylthiouracil, C. Amiodarone, D. Methimazole
D: Methimazole
Answer: D: Methimazole 
Explanation: Ans. (D) Methimazole(Ref: KDT 8/e p252-253)Methimazole inhibits only thyroid peroxidase whereas propylthiouracil inhibits thyroid peroxidase as well as 5'-deiodinase. Later is involved in peripheral conversion of T4 to T3 (Katzung 12/e p688, Goodman Gilman 12/e p1150)