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Patients with unprovoked venous thromboembolism (VTE) have higher risk for recurrent VTE after cessation of anticoagulant treatment than patients with provoked VTE (e.g., caused by immobilization). However, long-term anticoagulation for secondary prevention of VTE is controversial. In this systematic review and meta-analysis of 12 randomized trials (12,000 patients; follow-up range, 6–42 months), investigators compared the efficacy and safety of various oral anticoagulant drugs and aspirin.
All active treatments except low-dose aspirin significantly lowered risk for recurrent VTE. The number of recurrent VTE events (per 100 patients treated for 1 year) was 7 to 9 fewer with standard low-dose vitamin K antagonists (international normalized ratio, 2–3), dabigatran (Pradaxa), rivaroxaban (Xarelto), or apixaban (Eliquis) than with placebo or observation. The difference between placebo and aspirin (3 fewer events per 100 patients treated for 1 year) just failed to reach significance. Excess bleeding was noted with rivaroxaban and vitamin K antagonists (6 and 1 excess bleeding events, respectively, per 100 patients treated for 1 year). Fatal VTE and bleeding events were rare.
Castellucci LA et al. Efficacy and safety outcomes of oral anticoagulants and antiplatelet drugs in the secondary prevention of venous thromboembolism: Systematic review and network meta-analysis. BMJ 2013 Aug 30; 347:f5133. (http://dx.doi.org/10.1136/bmj.f5133)
Comment
Although vitamin K antagonists and novel anticoagulants lowered risk for recurrent venous thromboembolism, vitamin K antagonists and rivaroxaban were associated with excess risk for bleeding. Given this risk, the nuisance of monitoring vitamin K antagonists, and the costs of novel anticoagulants, many patients will balk at taking these drugs. Although aspirin didn't significantly lower risk for recurrent VTE in this meta-analysis, risk was lowered significantly in aspirin recipients in another recent analysis that employed different statistical techniques (NEJM JW Gen Med Nov 4 2012). Thus, aspirin might be a reasonable compromise for secondary prevention of VTE in some patients.