title: Duration of vitamin K antagonist therapy for venous thromboembolism: a systematic review of the literature.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Medicine, Division of Hematology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. mstreif@jhmi.edu
authors.forename: Michael B
authors.initials: MB
authors.lastname: Streiff
authors.forename: Jodi B
authors.initials: JB
authors.lastname: Segal
authors.forename: Leonardo J
authors.initials: LJ
authors.lastname: Tamariz
authors.forename: Mollie W
authors.initials: MW
authors.lastname: Jenckes
authors.forename: Dennis T
authors.initials: DT
authors.lastname: Bolger
authors.forename: John
authors.initials: J
authors.lastname: Eng
authors.forename: Jerry A
authors.initials: JA
authors.lastname: Krishnan
authors.forename: Eric B
authors.initials: EB
authors.lastname: Bass
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage* / Q000627:therapeutic use; D004334:Drug Administration Schedule; D006801:Humans; D016239:MEDLINE; D016032:Randomized Controlled Trials as Topic; D013923:Thromboembolism / Q000097:blood / Q000188:drug therapy*; D013997:Time Factors; D020246:Venous Thrombosis / Q000097:blood / Q000188:drug therapy*; D014812:Vitamin K / Q000037:antagonists & inhibitors*
chemical_list: D000925:Anticoagulants; D014812:Vitamin K