A diabetic female on INH and rifampicin for TB developed DVT.She was staed on warfarin, PT is not raised, and next step should be:: (A) Increase the dose of warfarin, (B) Replace warfarin with acenocoumarin, (C) Switch ethambutol for rifampicin, (D) Use LMW heparin
Answer is D. Rifampicin is a microsomal enzyme inducer and hence enhances the metabolism of warfarin. Hence warfarin can be replaced with a LMWH as the treatment is to stop warfarin. Acenocoumarin is a coumarin derivative similar to warfarin. From medical pharmacology padmaja 4th edition Page no 339,340