Deep venous thrombosis and pulmonary embolism. Part 2--Prevention of recurrences: warfarin or low-molecular-weight heparin for at least 3 months.

In patients with deep venous thrombosis or pulmonary embolism, initial treatment with low-molecular-weight heparin (LMWH) is primarily aimed at preventing thrombus extension. After this initial phase, the goal of treatment is to prevent recurrences, which can be fatal. Is it better to continue treatment of deep venous thrombosis or pulmonary embolism with LMWH or switch to an oral anticoagulant? What is the optimal duration of treatment? To answer these questions, we conducted a review of the literature using the standard Prescrire methodology. In non-cancer patients, two meta-analyses of trials in which treatment was not double blinded showed that severe bleeding was slightly less frequent with LMWH than with a vitamin K antagonist, but no data on mortality or the recurrence rate were provided. In cancer patients, LMWH prevented more recurrences than vitamin K antagonists; LMWH did not reduce overall mortality and did not increase the risk of serious bleeding compared to vitamin K antagonists. Treatment with LMWH requires daily injections and renal monitoring.Treatment with warfarin, the standard vitamin K antagonist, requires regular INR monitoring. There is no evidence that rivaroxaban or dabigatran has a better harm-benefit balance than warfarin for long-term treatment. After a first episode of proximal deep venous thrombosis or pulmonary embolism associated with an identified reversible trigger, several meta-analyses support a 3-month course of anticoagulation. Prolonged anticoagulant therapy is generally considered when there is no identified trigger or in case of a recurrence. Two double-blind randomised placebo-controlled trials failed to establish whether or not aspirin-based antiplatelet therapy given after discontinuation of anticoagulant therapy has a favourable harm-benefit balance. Various clinical practice guidelines published since 2006 recommend first-line treatment with a vitamin K antagonist for at least 3 months in patients without cancer, and continuation of LMWH therapy in patients with cancer. Overall, LMWH and warfarin have similar harm-benefit balances. In practice, it is best to choose between these drugs on a case-by-case basis, taking into account patient preferences, monitoring constraints, difficulty controlling the INR, the risk of bleeding and interactions, and the cost of treatment.