Duration of anticoagulant treatment for venous thrombosis.

Patients with deep-vein thrombosis require long-term anticoagulant treatment to prevent recurrent venous thromboembolism. Anticoagulant treatment should be continued for at least 3 months in patients with a first-episode of proximal deep-vein thrombosis. In patients with a second-episode of venous thromboembolism, treatment should probably be continued for at least 1 year, because stopping treatment at 3 to 6 months is associated with a high rate of recurrent venous thromboembolism. Indefinite treatment may be indicated in patients with a second-episode of venous thromboembolism, but further clinical trials are required to clarify the risk and benefit of indefinite treatment. Further clinical trials are also required to determine if a longer course of treatment is indicated for subgroups of patients based on clinical characteristics and laboratory features (such as those with idiopathic thrombosis versus postoperative thrombosis, and those with or without identifiable molecular markers of a high risk of recurrent venous thromboembolism such as the factor V Leiden gene mutation).