Low-dose warfarin prevents recurrent thromboembolism
The Journal of Family Practice. 2003 August;52(8):587-604
August 1, 2003|The Journal of Family Practice
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- BACKGROUND: Prolonging the duration of full-intensity oral anticoagulation can decrease the recurrence of venous thromboembolism, but it often increases the rate of major bleeding above an acceptable risk-benefit ratio. This trial evaluated the efficacy and safety of long-term, low-intensity warfarin for the prevention of recurrent venous thromboembolism.
- POPULATION STUDIED: This multicenter study included patients older than 30 years, with documented idiopathic venous thromboembolism who completed at least 3 months of uninterrupted full-dose warfarin therapy (target INR, 2.0–3.0). The median age was 53 years; 47% were female, approximately 87% were white, and 9% were African American. More than 37% had at least 2 previous venous thrombo-embolisms, over 25% had either factor V Leiden or a prothrombin mutation, and all patients were treated with full-dose warfarin for an average of 6 months before enrollment.
- STUDY DESIGN AND VALIDITY: This randomized, double-blind, placebo-controlled trial was conducted from July 1998 to December 2002. All patients were involved in a 28-day runin phase to ensure that they could have their warfarin titrated to an INR of 1.5 to 2.0 without exceeding a daily dose of 10 mg. This run-in phase also identified and excluded patients with <85% adherence to the treatment regimen.
- OUTCOMES MEASURED: The primary endpoint measured was recurrent venous thromboembolism. A composite endpoint was major hemorrhage (bleeding that required hospitalization or transfusion), recurrent venous thromboembolism, and death from any cause. New stroke events were also monitored.
- RESULTS: Due to early termination, the mean duration of follow-up was 2.1 years and the median INR in the warfarin group was 1.7, compared with 1.0 for placebo. Low-intensity warfarin reduced the risk of recurrent venous thromboembolism by 64% (hazard ratio [HR]=0.36; 95% confidence interval [CI], 0.19–0.67; P<.001; number needed to treat [NNT]=22). Warfarin reduced the composite endpoint by 48% (HR=0.52; 95% CI, 0.31–0.87; P=.01; NNT=26).
PRACTICE RECOMMENDATIONS
Low-intensity warfarin (target international normalized ratio [INR], 1.5–2.0) effectively prevents recurrent venous thromboembolism without increasing the risk of major bleeding when used long-term for secondary prophylaxis. This is a reasonable approach following at least 3 to 12 months of full-intensity warfarin after the initial thromboembolic event.
