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Cochrane Database of Systematic Reviews: Plain Language Summaries [Internet]. Chichester, UK: John Wiley & Sons, Ltd; 2003-.

Cochrane Database of Systematic Reviews: Plain Language Summaries [Internet].

A fixed daily dose of a low molecular weight heparin compared with an adjusted dose of unfractionated heparin for treating blood clots in the deep veins (venous thromboembolism)

This version published: 2011; Review content assessed as up-to-date: July 13, 2010.

Link to full article: [Cochrane Library]

Plain language summary

Treatment of blood clots in the deep veins, particularly of the legs and the blood vessels of the lungs, with subcutaneous injections of a fixed dose of low molecular weight heparin (LMWH) results in fewer haemorrhages and deaths than treatment with unfractionated heparin.

Blood clots that form after surgery, bed‐rest or for other reasons can block veins, lead to recurring symptoms, and may cause shortness of breath, chestpain or be fatal if they move to the lungs. Unfractionated heparin is an older drug that thins the blood and is given either intravenously or by subcutaneous injection. Blood clotting factors have to be monitored carefully and the dose adjusted because of the variability of its effect.

This review of 23 randomized controlled trials involving 9587 participants found that low molecular weight heparin is at least as good as unfractionated heparin for treating blood clots by reducing their size and preventing their recurrence. It is also better at preventing haemorrhages and deaths.


Background: Low molecular weight heparins (LMWHs) have been shown to be effective and safe in preventing venous thromboembolism (VTE). They may also be effective for the initial treatment of VTE. This is an update of a Cochrane review first published in 1999 and previously updated in 2004.

Objectives: To determine the effect of LMWH compared with unfractionated heparin (UFH) for the initial treatment of VTE.

Search methods: Trials were identified by searching the Cochrane Peripheral Vascular Diseases Group Specialised Register and CENTRAL (The Cochrane Library). Colleagues and pharmaceutical companies were contacted for additional information.

Selection criteria: Randomised controlled trials comparing fixed dose subcutaneous LMWH with adjusted dose intravenous or subcutaneous UFH in people with VTE.

Data collection and analysis: Two review authors assessed trials for inclusion and quality, and extracted data independently.

Main results: Twenty‐three studies were included (n = 9587). Thrombotic complications occurred in 3.6% of participants treated with LMWH compared with 5.3% treated with UFH (odds ratio (OR) 0.70; 95% confidence interval (CI) 0.57 to 0.85). Thrombus size was reduced in 53% of participants treated with LMWH and 45% treated with UFH (OR 0.69; 95% CI 0.59 to 0.81). Major haemorrhages occurred in 1.1% of participants treated with LMWH compared with 1.9% treated with UFH (OR 0.58; 95% CI 0.40 to 0.83). In 19 trials, 4.3% of participants treated with LMWH died compared with 5.8% of participants treated with UFH (OR 0.77; 95% CI 0.63 to 0.93).

Nine studies (n = 4451) examined proximal thrombosis, 2192 participants were treated with LMWH and 2259 with UFH. Subgroup analysis showed statistically significant reductions favouring LMWH in thrombotic complications and major haemorrhage. By end of follow up, 80 (3.6%) participants treated with LMWH had thrombotic complications compared with 143 (6.3%) treated with UFH (OR 0.57; 95% CI 0.44 to 0.75). Major haemorrhages occurred in 18 (1.0%) participants treated with LMWH compared with 37 (2.1%) treated with UFH (OR 0.50; 95% CI 0.29 to 0.85). Nine studies showed a statistically significant reduction in mortality favouring LMWH. By the end of follow up, 3.3% (70/2094) of participants treated with LMWH had died and 5.3% (110/2063) treated with UFH.

Authors' conclusions: Fixed dose LMWH is more effective and safer than adjusted dose UFH for the initial treatment of VTE. Compared to UFH, LMWH significantly reduced the incidence of thrombotic complications, the occurrence of major haemorrhage during initial treatment and overall mortality at follow up.

Editorial Group: Cochrane Peripheral Vascular Diseases Group.

Publication status: Edited (no change to conclusions).

Citation: Erkens PMG, Prins MH. Fixed dose subcutaneous low molecular weight heparins versus adjusted dose unfractionated heparin for venous thromboembolism. Cochrane Database of Systematic Reviews 2010, Issue 9. Art. No.: CD001100. DOI: 10.1002/14651858.CD001100.pub3. Link to Cochrane Library. [PubMed: 20824828]

Copyright © 2011 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.

PMID: 20824828

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