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Duration of vitamin K antagonist therapy for venous thromboembolism: a systematic review of the literature.

Streiff MB, Segal JB, Tamariz LJ, Jenckes MW, Bolger DT, Eng J, Krishnan JA, Bass EB

Department of Medicine, Division of Hematology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. mstreif@jhmi.edu

PURPOSE: The aim of this study was to evaluate the evidence on the optimal duration of vitamin K antagonist (VKA) therapy for venous thromboembolism (VTE). METHODS: Randomized controlled trials of VKA for VTE were identified by a computerized database search. Summary event rates for relevant outcomes were calculated using a random effects model with 95% confidence intervals (95% CI). RESULTS: Ten studies met inclusion criteria. The incidence of recurrent VTE (3 months, 7.9 VTE per 100 patient-years [95% CI, 5.2 to 10] versus 4-12 months, 4.9 VTE per 100 patient-years [95% CI, 3.6 to 6.2] versus continuous therapy, 0.7 VTE per 100 patient-years [95% CI, 0.3 to 1.1]) and total adverse events (3 months, 11.2 events per 100 patient-years [95%CI, 7.1 to 15.4] versus 4-12 months, 7.4 events per 100 patient-years [95%CI, 6.2 to 8.5] versus continuous therapy 3.1 events per 100 patient-years [95%CI, 2.2 to 4.0] declined as VKA therapy duration increased. Continuous reduced intensity therapy (INR 1.5-2) was associated with more recurrent VTE (2.3 VTE per 100 patient-years [95%CI, 1.5 to 3.0]). Continuous VKA therapy (INR 2-3) was beneficial for patients with a second VTE and antiphospholipid antibodies. The incidence of recurrent VTE was similar with 6 or 12 weeks of therapy for isolated calf DVT. CONCLUSION: Randomized controlled trials indicate that continuous VKA therapy (INR 2-3) for VTE is associated with better clinical outcomes than shorter durations. Patients with a second VTE or antiphospholipid antibodies also benefit from continuous anticoagulation. Patients with calf DVT should be treated for at least 6 weeks.

Published 28 August 2006 in Am J Hematol, 81(9): 684-91.
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