Enzalutamide-warfarin interaction necessitating warfarin dosage adjustment: A case report of successful clinical management

SummaryWhat 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.