<prompt> All of the following drugs increase bleeding when given to a patient on warfarin EXCEPT:IsoniazidAmiodaroneCarbamazepineCimetidine  <response>: 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. 