<prompt> Therapeutic monitoring of plasma level of drug is done when using all of the following drugs exceptWarfarinGentamicinCyclosporinePhenytoin  <response>: Ans. A WarfarinRef: KDT 8the p42Therapeutic drug monitoring is not required for oral anticoagulants like warfarin. The effect of warfarin is monitored by measuring prothrombin time or INR International Normalized Ratio. 