Three Months vs. One Year of Oral Anticoagulant Therapy For Idiopathic Deep Venous Thrombosis - Anticoagulant Therapy For Idiopathic Deep Venous Thrombosis


Three Months vs. One Year of Oral Anticoagulant Therapy For Idiopathic Deep Venous Thrombosis.


Extending the duration of anticoagulant therapy beyond 3 months in patients with idiopathic deep venous thrombosis (DVT) may decrease recurrent thrombosis during the period of therapy. Does the benefit persist after anticoagulant therapy is discontinued?

Study Design

Study Design:

Patients Enrolled: 134
Female: 44

Drug/Procedures Used:

Patients with a first episode of idiopathic DVT who had completed 3 months of warfarin were randomly assigned to discontinuation or continuation for an additional 9 months. The primary outcome, based on intention to treat, was the recurrence of symptomatic confirmed venous thromboembolism (VTE), DVT and pulmonary embolism, during at least 2 years of follow-up. Warfarin dose was adjusted to a target INR of 2.0 to 3.0 in anticoagulant clinics.

Principal Findings:

Average age was 68 and 56% were men. The INR was within the target range 81% of the time during the additional 9 months of therapy. Of the 134 patients assigned to continue therapy, 21 had recurrent VTE (15.7%, average follow-up 37.8 month), as did 21 of the 133 patients assigned to discontinue therapy (15.8%, average follow-up 37.2 month). All recurrent VTE episodes were idiopathic and none was fatal. The average time to recurrence was 11.2 month from randomization in patients assigned to discontinue therapy and 16 month in those continuing therapy. The risk of recurrence during the first 9 months following randomization among patients who took the assigned warfarin was 1.2% per patient year, relative risk compared to discontinued therapy, 0.09, 95% CI 0.02-0.69, p=0.003. After discontinuation of therapy, the incidence of recurrence was 5% per patient year in both groups. Major bleeding occurred in 3% of those assigned to warfarin vs. 1.5% of control. None of these patients had an INR above the therapeutic range.

In patients with DVT the benefit associated with extending the duration of anticoagulant therapy to one year is not maintained after the therapy is discontinued.


While the benefit does not extend beyond the treatment period in idiopathic DVT and morbidity associated with DVT was very low, warfarin was clearly effective. If the bleeding rate and inconvenience of monitoring can be reduced, long-term therapy may be warranted, particularly in high-risk subsets with inherited hypercoagulability, which was not assessed in this study. The value of such a strategy is being tested in PREVENT, an NHLBI study designed to test the utility of long-term low-dose warfarin.


Agnelli G, Prandoni P, Santamaria MG, et al. and the Warfarin Optimal Duration Italian Trial Investigators. N Engl J Med 2001;345:165-9.

Clinical Topics: Anticoagulation Management, Pulmonary Hypertension and Venous Thromboembolism, Vascular Medicine, Anticoagulation Management and Venothromboembolism

Keywords: Thrombophilia, Pulmonary Embolism, Warfarin, Intention to Treat Analysis, Venous Thromboembolism, Venous Thrombosis, Hemorrhage

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