ABSTRACT
WHAT IS KNOWN AND OBJECTIVES: Enzalutamide package labeling recommends avoiding concurrent warfarin use due to potential reductions in warfarin concentrations via enzalutamide-associated hepatic enzyme induction. A case of successful management of this interaction via warfarin adjustments is reported. CASE DESCRIPTION: A 77-year-old Caucasian male, previously relatively stable on warfarin 42-45 mg weekly, reported to clinic after the recent start of enzalutamide and subsequent hospitalization with a subtherapeutic International Normalized Ratio (INR). A 50% increase in weekly warfarin dose resulted in a therapeutic INR. Enzalutamide was temporarily discontinued, and a 33% weekly warfarin dose decrease resulted in two therapeutic INRs. WHAT IS NEW AND CONCLUSION: This is the first case to highlight the clinical significance of this interaction, noting that patients taking enzalutamide may require approximately 30%-50% adjustment in their warfarin dosage to maintain a therapeutic INR.
