Study Suggests Changes Needed in Warfarin Dosing
Warfarin is highly efficacious for the prevention of stroke and the treatment of venous thromboembolism, as well as for other indications (e.g., atrial fibrillation). However, relatively little is known about how best to manage warfarin once it is initiated. The lack of evidence regarding optimal management strategies probably contributes to limited success in maintaining patients within the target International Normalized Ratio (INR) range (system used to report testing for coagulation). This observational study sought to provide insight into optimal dose management strategies to improve stability of INR control. Investigators analyzed data for 3,961 patients receiving warfarin from 94 community-based clinics. Patients were observed for a mean of 15.2 months, and 62% of patients received the drug related to a diagnosis of atrial fibrillation.
Findings show that providers vary widely in their dose change thresholds in similar clinical situations. The dose of warfarin was decreased at 14.4% of visits, increased at 16.4% of visits, and remained the same at 69.3% of visits. The INR value was by far the most important predictor of dose change. On average clinicians changed the patient’s dose when the INR was 1.8 or lower/3.2 or higher; however, optimal management would have been to change the dose when the INR was 1.7 or lower/3.3 or higher. This relatively minor change in management would be expected to increase time in the therapeutic INR range from 68% to 74%. Authors suggest that in addition to offering warfarin to as many optimal candidates as possible, we also need to optimize warfarin dose management to fully realize the benefits of anticoagulation.
Rose A, Ozonoff A, Berlowitz D, Henault L, and Hylek E. Warfarin dose management affects INR control. Journal of Thrombosis and Haemostasis January 2009;7(1):94-101.
Dr. Rose is supported by an HSR&D Career Development Award. Drs. Rose and Berlowitz are part of HSR&D’s Center for Health Quality, Outcomes, and Economic Research in Bedford, MA.
