Comparison of fixed-dose weight-adjusted unfractionated heparin and low-molecular-weight heparin for acute treatment of venous thromboembolism.

Context: When unfractionated heparin is used to treat acute venous thromboembolism, it is usually administered by intravenous infusion with coagulation monitoring, which requires hospitalization. However, subcutaneous administration of fixed-dose, weight-adjusted, unfractionated heparin may be suitable for inpatient and outpatient treatment of venous thromboembolism.

Objective: To determine if fixed-dose, weight-adjusted, subcutaneous unfractionated heparin is as effective and safe as low-molecular-weight heparin for treatment of venous thromboembolism.

Design, Setting, And Patients: Randomized, open-label, adjudicator-blinded, noninferiority trial of 708 patients aged 18 years or older with acute venous thromboembolism from 6 university-affiliated clinical centers in Canada and New Zealand conducted from September 1998 through February 2004. Of the randomized patients, 11 were subsequently excluded from the analysis of efficacy and 8 from the analysis of safety.

Interventions: Unfractionated heparin was administered subcutaneously as an initial dose of 333 U/kg, followed by a fixed dose of 250 U/kg every 12 hours (n = 345). Low-molecular-weight heparin (dalteparin or enoxaparin) was administered subcutaneously at a dose of 100 IU/kg every 12 hours (n = 352). Both treatments could be administered out of hospital and both were overlapped with 3 months of warfarin therapy.

Main Outcome Measures: Recurrent venous thromboembolism within 3 months and major bleeding within 10 days of randomization.

Results: Recurrent venous thromboembolism occurred in 13 patients in the unfractionated heparin group (3.8%) compared with 12 patients in the low-molecular-weight heparin group (3.4%; absolute difference, 0.4%; 95% confidence interval, -2.6% to 3.3%). Major bleeding during the first 10 days of treatment occurred in 4 patients in the unfractionated heparin group (1.1%) compared with 5 patients in the low-molecular-weight heparin group (1.4%; absolute difference, -0.3%; 95% confidence interval, -2.3% to 1.7%). Treatment was administered entirely out of hospital in 72% of the unfractionated heparin group and 68% of the low-molecular-weight heparin group.

Conclusion: Fixed-dose subcutaneous unfractionated heparin is as effective and safe as low-molecular-weight heparin in patients with acute venous thromboembolism and is suitable for outpatient treatment.

Trial Registration: clinicaltrials.gov Identifier: NCT00182403.