Anticoagulant effect of warfarin is increased by all of the following except-

Ans. is 'b' i.e., Phytonadione o Warfarin shows a number of drug interactions and requires dose adjustment :? 1) Enzyme inducers (phenobarbitone, rifampicin, phenytoin, griseofulvin etc) and oral contraceptives (increase clotting factors) decrease the effect and hence require increase in dose of warfarin. 2) Drugs that increase the effect of warfarin and require dose reduction are enzyme inhibitors (cimetidine, erythromycin, cotrimoxazole, disulfiram, isoniazid, metronidazole, azoles, allopurinol), cephalosporins (cefamendole, cefoperazone, moxalactam), phenylbutazone, amiodarone, sulfinpyrazone, acute alcohol intake, loop diuretics and valproate.