Clinical study
Low-molecular-weight heparins and unfractionated heparin in the treatment of patients with acute venous thromboembolism: Results of a meta-analysis

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Purpose

To obtain reliable estimates of the relative efficacy and safety of low-molecular-weight heparins (LMWHs) and unfractionated heparin (UFH) in the treatment of patients with venous thromboembolism.

Methods

A literature search of randomized trials evaluating LMWH and UFH for the period from 1980 to 1994 was conducted to obtain data for a meta-analysis. Studies were classified as level 1 if they were double-blind or if there was blinded assessment of outcome measures, and level 2 if they did not provide assurance of blinded outcome assessment.

Results

In level 1 studies, the relative risk (RR) of recurrent venous thromboembolism during the first 15 days and over the entire period of anticoagulant therapy was 0.24 (95% confidence intervals [Cl] 0.06 to 0.80, P = 0.02) and 0.39 (95% Cl 0.30 to 0.80, P = 0.006), respectively, in favor of LMWH treatment. The RR for major bleeding was 0.42 (95% Cl 0.2 to 0.9, P = 0.01), in favor of LMWH. In level 2 studies, no significant differences in the rates of recurrent venous thromboembolism or major bleeding were observed. Pooling level 1 and level 2 studies, the RR for overall mortality and mortality in cancer patients was 0.51 (95% Cl 0.2 to 0.9, P = 0.01) and 0.33 (95% Cl 0.1 to 0.8, P = 0.01), respectively, in favor of LMWH.

Conclusions

LMWH are likely to be more effective than UFH in preventing recurrent venous thromboembolism, to produce less major bleeding, and to be associated with a lower mortality rate, particularly in the subgroup of patients with cancer.

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    1

    Dr. Sergio Siragusa is a recipient of a Grant for Thrombosis Research from IRCCS Policlinico S. Matteo, Pavia, Italy.

    2

    Dr. Hirsh is a Distinguished Professor of the Heart and Stroke Foundation of Canada.

    3

    Dr. Ginsberg is a recipient of a Research Scholarship of the Heart and Stroke Foundation of Canada.

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