Effects of Dicloxacillin on Warfarin Dose in Patients With a Left Ventricular Assist Device

Patients with a durable, continuous flow left ventricular assist device (CF-LVAD) require anticoagulation with warfarin to prevent thromboembolic events. Driveline infections (DLIs) are a common CF-LVAD complication. A common pathogen implicated in DLI is oxacillin-sensitive Staphylococcus aureus (OSSA), which is effectively treated by oral dicloxacillin. Previous published experiences have observed a significant drug interaction between dicloxacillin and warfarin resulting in decreased international normalized ratio (INR) and increased warfarin dosing requirements. We sought to analyze the effect of dicloxacillin on INR and warfarin dose when used for DLI in our CF-LVAD program. Five of 106 patients having received an CF-LVAD at our institution met the inclusion criteria for this case series. These patients required a mean 51.8% (standard deviation of 29.8%) weekly warfarin dose increase to restore INR to the therapeutic range after the addition of dicloxacillin. Three of the five patients subsequently had their dicloxacillin discontinued, with a mean decrease in weekly warfarin dose of 30.6% (standard deviation of 19.1%). In our experience, when coalesced with prior published reports, an empiric warfarin dose increase of 25% to 33% is reasonable upon initiation of dicloxacillin and an empiric warfarin dose reduction of 10% to 15% is recommended upon discontinuation of dicloxacillin. Close INR follow-up is warranted during and after dicloxacillin treatment.