This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Adverse Drug Effect, Subject name: Pharmacology
All of the following drugs increase bleeding when given to a patient on warfarin EXCEPT: 
Select and explain. 
A. Isoniazid, B. Amiodarone, C. Carbamazepine, D. Cimetidine
C: Carbamazepine
Answer: C: Carbamazepine 
Explanation: Ans. C. CarbamazepineWarfarin constitutes S as well as R enantiomers. S Warfarin is the most active form:* Metabolism of S warfarin is by CYP2C9 leading to the formation of 7-OH warfarin* Metabolism of R warfarin is by CYP1A1, CYP1A2, CYP3A4 leading to the formation of 6-OH warfarin, 8-OH warfarin, 10-OH warfarinAs Carbamazepine is enzyme inducer, it induces metabolism of warfarin and hence warfarin concentration decreases and it can lead to therapeutic failureRest of drugs: Isoniazid, Amiodarone, cimetidine are microsomal enzyme inhibitors leading to warfarin toxicity and can lead to bleeding.