Newer Cephalosporins (Cefamandole, Moxalactum, and Cefoperazone) cause hypoprothrombinemia. Thus, when anticoagulants are given with cephalosporins they have an additive anticoagulant action. * Imidazoles like ketoconazole and fluconazole affect hepatic drug metabolism and lead to raised plasma level of warfarin. * Macrolides inhibit hepatic oxidation of many drugs leading to raised plasma level of warfarin.