Warfarin Dosing and Body Mass Index

Abstract

Warfarin is still the most commonly used anticoagulant for the treatment of venous thromboembolism and other hypercoagulable states. Warfarin metabolism is affected by multiple factors, including diet, medications, and individual patient characteristics. As both underdosing and overdosing can increase risks to patients, several studies have attempted to develop dosing protocols. However, few have investigated how patient weight and body mass index (BMI) affect warfarin dosing. The objective of this study was to determine the association between BMI and the total weekly dose (TWD) of warfarin. In this retrospective study, we identified patients taking warfarin who had an international normalized ratio (INR) within the therapeutic range to assess if there was a significant correlation between TWD, that is, maintenance warfarin dosing, and BMI in obese and nonobese patients. A total of 831 patients were studied, with a BMI range between 13.4 and 63.1 kg/m(2). We found that BMI is positively correlated with the total weekly warfarin dose. Our study showed that for each 1-point increase in BMI, the weekly warfarin dose increased by 0.69 mg. We found that the average warfarin weekly dose in this population can be estimated using the formula: 12.34 + 0.69 × BMI. There is an association between BMI and the TWD of warfarin. This could have dosing implications for both patients and prescribers, as patients with a high BMI will be expected to require higher doses of warfarin to maintain a therapeutic INR.