Elevated INR Following Coadministration of Warfarin with Fenofibrate: A Case Report and Review of the Literature

Abstract

Fenofibrate, a lipid lowering drug, can increase the effects of warfarin and may cause bleeding more easily. We report a case of a 58-year-old Thai male patient who was administered warfarin at 27 mg per week to achieve the target international normalized ratio (INR) value. Fenofibrate at 200 mg per day was coadministered with warfarin for three months. The patient’s INR value increased to 5.38, but he did not experience any abnormal bleeding. His compliance with the medication regime was good, and he denied using other medications or herbal and dietary supplements. Warfarin was subsequently withheld for three days then resumed at the same dose after the INR value had returned to the normal range. Concurrently, fenofibrate was discontinued because his triglyceride level declined to below the normal target. One week later, his INR value had decreased to 2.44. This case presents an increased INR value when fenofibrate was concomitantly used with warfarin. This occurs because fenofibrate inhibits the CYP2C9 enzyme and displaces the protein albumin, thereby increasing the effect of warfarin. These results are consistent with several other case reports. The onset of this effect occurs approximately one week to one month after initiating fenofibrate . Healthcare professionals should carefully monitor INR values to ensure safe and efficacious management in patients using both warfarin and fenofibrate.