INR

Abstract

Case reports in western populations reported that fenofibrate enhances the anticoagulatory effect of warfarin. We are reporting ten cases of warfarin-fenofibrate interaction among Malaysian patients’ cases that were managed at the anticoagulation clinic of Hospital Kuala Lumpur. Patients taking warfarin and micronized fenofibrate 145mg daily concurrently between the year 2014 to 2018 were identified in May 2018. Ten active patients were included, and the relevant data were retrieved retrospectively. All patients received warfarin for stroke prevention in atrial fibrillation (AF), with a target international normalised ratio (INR) of 2 to 3. No dose adjustment was done upon initiation of fenofibrate. Warfarin doses were adjusted to achieve the targeted range but fenofibrate was not discontinued. Eight patients had INR levels above the target range when INR being reassessed between 20 to 62 days after initiation of fenofibrate. Their weekly warfarin doses were between 17.5mg-46.5mg. Baseline INR ranged between 1.6 -3.1. Percentage of dose reduction ranged between 5%-60%. Four of the patients were on other concurrent interacting medications such as statin and levothyroxine. Only one patient, whose case was with an INR 3.1 before initiation of fenofibrate, required admission for hematoma (INR 12). Two patients had INR within the target range, and INR were assessed at 14 and 21 days after fenofibrate initiation. Their weekly warfarin doses were between 24.5mg and 26.5mg while baseline INR was 2.8 and 1.9 respectively. Interaction between fenofibrate and warfarin may increase INR among Malaysian patients, thus close monitoring of INR is warranted. Empirical warfarin dose reduction may be considered upon initiation of this drug combination for patients with AF. The next INR reassessment date should be arranged not later than three weeks after initiation of fenofibrate.