Three months versus one year of oral anticoagulant therapy for idiopathic deep venous thrombosis.

Background: In patients with idiopathic deep venous thrombosis, continuing anticoagulant therapy beyond three months is associated with a reduced inci dence of recurrent thrombosis during the period of therapy. Whether this be nefit persists after anticoagulant therapy is discontinued is controversial . Methods: Patients with a first episode of idiopathic proximal deep venous t hrombosis who had completed three months of oral anticoagulant therapy were randomly assigned to the discontinuation of oral anticoagulants or to thei r continuation for nine additional months. The primary study outcome was re currence of symptomatic, objectively confirmed venous thromboembolism durin g at least two years of follow-up. Results: The primary intention-to-treat analysis showed that of 134 patient s assigned to continued oral anticoagulant therapy, 21 had a recurrence of venous thromboembolism (15.7 percent; average follow-up, 37.8 months), as c ompared with 21 of 133 patients assigned to the discontinuation of oral ant icoagulant therapy (15.8 percent; average follow-up, 37.2 months), resultin g in a relative risk of 0.99 (95 percent confidence interval, 0.57 to 1.73) . During the initial nine months after randomization (after all patients re ceived three months of therapy), 1 patient had a recurrence while receiving oral anticoagulant therapy (0.7 percent), as compared with 11 of the patie nts assigned to the discontinuation of oral anticoagulant therapy (8.3 perc ent, P=0.003). The incidence of recurrence after the discontinuation of tre atment was 5.1 percent per patient-year in patients in whom oral anticoagul ant therapy was discontinued after 3 months and 5.0 percent per patient-yea r in patients who received an additional 9 months of oral anticoagulant the rapy. None of the recurrences were fatal. Four patients had nonfatal major bleeding during the extended period of anticoagulant therapy (3.0 percent). Conclusions: In patients with idiopathic deep venous thrombosis, the clinic al benefit associated with extending the duration of anticoagulant therapy to one year is not maintained after the therapy is discontinued. (N Engl J Med 2001;345:165-9.) Copyright (C) 2001 Massachusetts Medical Society.