Low intensity warfarin: is it clinically useful in venous thromboembolism management?

Therapy for a first episode of venous thromboembolism (VTE) typically includes a vitamin K antagonist, such as warfarin, for 3-6 months at an international normalized ratio (INR) of 2-3. After the cessation of warfarin therapy, unprovoked VTE is associated with a recurrence rate of 5-15% per year. Prolonging initial therapy does not reduce the recurrence risk once warfarin is discontinued and is not routinely recommended for such patients. The Prevention of Recurrent Venous Thromboembolism (PREVENT) and Extended Low-Intensity Anticoagulation for Thromboembolism (ELATE) trials were undertaken to evaluate the efficacy and safety of low-intensity warfarin (INR 5-2) in this population. While both trials demonstrated that low-intensity warfarin offers substantial protection against recurrent VTE, only the ELATE trial included a standard intensity arm; this arm showed a significantly lower recurrence rate and a major bleed rate that, surprisingly, was similar to the low-intensity arm. There still remains no consensus that long-term warfarin at an INR of 2-3 should be recommended for all patients who sustain a first unprovoked venous thromboembolic event, which largely stems from our current inability to reliably identify those patients most likely to develop recurrences. Given that an individualized approach is required in deciding the duration of anticoagulation, it is the author's belief that low-intensity warfarin, which the PREVENT trial demonstrated could be monitored every other month, is a useful option for some patients with a first episode of VTE.