title: A comparison of six weeks with six months of oral anticoagulant therapy after a first episode of venous thromboembolism. Duration of Anticoagulation Trial Study Group.
abstract: BACKGROUND
  The optimal duration of oral anticoagulant therapy after a first episode of venous thromboembolism is still a matter of debate.
  
  
  METHODS
  We performed a multicenter trial comparing six weeks of oral anticoagulant treatment with six months of such therapy in patients who had a first episode of venous thromboembolism. Anticoagulant therapy consisted of warfarin or dicumarol. Of the 902 patients enrolled, 5 were later excluded because they had congenital protein C deficiency; 443 were randomly assigned to receive six weeks of oral anticoagulant therapy with a targeted international normalized ratio (INR) of 2.0 to 2.85, and 454 were randomly assigned to receive six months of such therapy. The initial diagnoses were confirmed by means of venography in cases of deep-vein thromboses (n = 790) and with perfusion-ventilation scanning or angiography in cases of pulmonary embolism (n = 107); recurrences were confirmed in the same way.
  
  
  RESULTS
  After two years of follow-up, there had been 123 recurrences of venous thromboembolism that met the diagnostic criteria, 80 in the six-week group (18.1 percent; 95 percent confidence interval, 14.5 to 21.6) and 43 in the six-month group (9.5 percent; 95 percent confidence interval, 6.8 to 12.2). The odds ratio for recurrence in the six-week group was 2.1 (95 percent confidence interval, 1.4 to 3.1). There was no difference in mortality or the rate of major hemorrhage between the six-week and six-month groups.
  
  
  CONCLUSIONS
  Six months of prophylactic oral anticoagulation after a first episode of venous thromboembolism led to a lower recurrence rate than did treatment lasting for six weeks. The difference between the two groups occurred between 6 weeks and 6 months after the start of treatment, and the rates of recurrence remained nearly parallel for 1 1/2 years thereafter.
authors.affiliation: Department of Internal Medicine, Karolinska Hospital, Stockholm, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Schulman
authors.forename: A S
authors.initials: AS
authors.lastname: Rhedin
authors.forename: P
authors.initials: P
authors.lastname: Lindmarker
authors.forename: A
authors.initials: A
authors.lastname: Carlsson
authors.forename: G
authors.initials: G
authors.lastname: Lärfars
authors.forename: P
authors.initials: P
authors.lastname: Nicol
authors.forename: E
authors.initials: E
authors.lastname: Loogna
authors.forename: E
authors.initials: E
authors.lastname: Svensson
authors.forename: B
authors.initials: B
authors.lastname: Ljungberg
authors.forename: H
authors.initials: H
authors.lastname: Walter
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use*; D005260:Female; D005500:Follow-Up Studies; D006470:Hemorrhage / Q000209:etiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011336:Probability; D011655:Pulmonary Embolism / Q000150:complications / Q000188:drug therapy* / Q000401:mortality; D012008:Recurrence; D015912:Thrombolytic Therapy; D013924:Thrombophlebitis / Q000150:complications / Q000188:drug therapy* / Q000401:mortality; D016896:Treatment Outcome
chemical_list: D000925:Anticoagulants