Warfarin resistance in a patient with prosthetic valve endocarditis treated with cloxacillin

ABSTRACT

Systemic anticoagulation with warfarin is the mainstay therapy for patients with valve prosthesis. Such drug therapy is of crucial importance in patients with prosthetic valve endocarditis [PVE] because of higher incidence of thrombo-embolism. We are reporting a case of PYE where the patient developed warfarin resistance due to Cloxacillin administration in spite of concomitant administration of I.V. Heparin. Warfarin dose was increased from a baseline of 5 mg daily before Cloxacillin was started to 30 mg daily during Cloxacillin treatment. Six weeks after completion and discontinuing the antibiotic course, the patient's International Normalized ratio [INR] value gradually increased and Warfarin dose was tapered down over eight days. Cloxacillin-Warfarin interaction seems to be due to rapid metabolism in susceptible subjects leading to a reduction in the hypoprothombinemic effect of warfarin. Our finding is consistent with the reported cases which documented such interaction with other members of Penicillinase-resistant Penicillins such as NafcilIin and Dicloxacillin