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Am Fam Physician. 2005;72(01):75-76

Clinical Scenario

A 72-year-old woman presents with swelling and pain in her calf that has lasted two days. Evaluation reveals that she has an acute thromboembolism of the deep femoral vein.

Clinical Question

Should venous thromboembolism initially be treated with unfractionated heparin or a low-molecular-weight heparin (LMWH)?

Evidence-Based Answer

LMWH is safer and more effective than unfractionated heparin for initial treatment of venous thromboembolism.

Practice Pointers

The standard treatment of acute venous thromboembolism has been unfractionated heparin administered intravenously for five to 10 days until adequate anticoagulation can be achieved with oral agents. However, the more predictable anticoagulant effect of LMWHs, a number of which have been approved in the past decade, allows standard doses to be given without laboratory monitoring in appropriate patients. Additionally, by effecting a steady state of adequate anticoagulation more quickly and consistently, LMWH may reduce hemorrhage caused by excessive anticoagulation and increase treatment efficacy.

Van Dongen and associates1 analyzed studies comparing the effects of unfractionated heparin and LMWH in patients with venous thromboembolism and evaluated differences between the treatments in symptomatic recurrence of venous thromboembolism, change in thrombus size, rate of hemorrhage, and overall mortality. Eight different preparations of LMWH or heparinoid were used in the trials (i.e., nadroparin, tinzaparin, enoxaparin, dalteparin, CY 222, certoparin, ardeparin, and reviparin). The results showed LMWH to be superior in efficacy to unfractionated heparin, with fewer thrombotic complications (number needed to treat [NNT] to prevent one complication = 37) and more frequent reduction in thrombus size (NNT = 13). Furthermore, LMWH was found to be safer, being associated with fewer instances of major hemorrhage (NNT = 125) and fewer deaths (NNT = 67).

Of the 22 trials included in the review, six involved patients with malignant disease (a common risk factor for venous thromboembolism). These six trials showed a reduction in mortality with LMWH, whereas no statistically significant reduction in mortality was found in the 16 trials involving patients without cancer.

Thirteen of the 22 trials excluded patients with pulmonary embolus, while two trials included patients with pulmonary embolus exclusively. Five trials included patients with isolated symptomatic distal venous thromboembolism as well as those with proximal venous thromboembolism. Although the reviewers of this article1 felt that no firm recommendation could be made about initial treatment of pulmonary embolism, a recent meta-analysis2 concluded that LMWH “appears to be as effective and safe as dose-adjusted intravenous unfractionated heparin for the initial treatment of nonmassive pulmonary embolism.”

Cochrane Abstract

Background. Low-molecular-weight heparins (LMWHs) have been shown to be effective and safe in preventing venous thromboembolism, and also may be effective for the initial treatment of this condition.

Objectives. To determine the effect of LMWH compared with unfractionated heparin for the initial treatment of venous thromboembolism.

Search Strategy. The authors1 identified trials from the Cochrane Peripheral Vascular Diseases Group’s Specialised Register, CENTRAL, and LILACS. They also contacted colleagues and pharmaceutical companies for additional information.

Selection Criteria. The authors selected randomized controlled trials comparing fixed-dose subcutaneous LMWH with adjusted-dose intravenous or subcutaneous unfractionated heparin in persons with venous thromboembolism.

Data Collection and Analysis. At least two reviewers assessed trials for inclusion and quality, and extracted data independently.

Primary Results. Twenty-two studies (n = 8,867) were included in the analysis. Thrombotic complications occurred in 151 of 4,181 (3.6 percent) participants treated with LMWH, compared with 211 of 3,941 (5.4 percent) participants treated with unfractionated heparin (odds ratio [OR], 0.68; 95 percent confidence interval [CI], 0.55 to 0.84; 18 trials). Thrombus size was reduced in 53 percent of participants treated with LMWH and in 45 percent of those treated with unfractionated heparin (OR, 0.69; 95 percent CI, 0.59 to 0.81; 12 trials). Major hemorrhages occurred in 41 of 3,500 (1.2 percent) participants treated with LMWH, compared with 73 of 3,624 (2.0 percent) participants treated with unfractionated heparin (OR, 0.57; 95 percent CI, 0.39 to 0.83; 19 trials). In 18 trials, 187 of 4,193 (4.5 percent) participants treated with LMWH died, compared with 233 of 3,861 (6.0 percent) participants treated with unfractionated heparin (OR, 0.76; 95 percent CI, 0.62 to 0.92).

Nine studies (n = 4,451) examined proximal thrombosis; 2,192 participants were treated with LMWH and 2,259 with unfractionated heparin. Subgroup analysis showed statistically significant reductions favoring LMWH in thrombotic complications and major hemorrhage. By the end of follow-up, 80 (3.6 percent) participants treated with LMWH had thrombotic complications, compared with 143 (6.3 percent) treated with unfractionated heparin (OR, 0.57; 95 percent CI, 0.44 to 0.75). Major hemorrhage occurred in 18 (1.0 percent) participants treated with LMWH, compared with 37 (2.1 percent) treated with unfractionated heparin (OR, 0.50; 95 percent CI, 0.29 to 0.85). Nine studies (n = 4,157) showed a statistically significant reduction favoring LMWH with respect to mortality. By the end of follow-up, 3.3 percent (70 of 2,094) of participants treated with LMWH had died, compared with 5.3 percent (110 of 2,063) of participants treated with unfractionated heparin (OR, 0.62; 95 percent CI, 0.46 to 0.84).

Reviewers’ Conclusions. LMWH is more effective than unfractionated heparin for the initial treatment of venous thromboembolism. LMWH significantly reduces the occurrence of major hemorrhage during initial treatment and overall mortality at follow-up.

These summaries have been derived from Cochrane reviews published in the Cochrane Database of Systematic Reviews in the Cochrane Library. Their content has, as far as possible, been checked with the authors of the originalreviews, but the summaries should not be regarded as an official product of the Cochrane Collaboration; minorediting changes have been made to the text (

Another advantage of LMWH is the less intense nursing care and laboratory monitoring that it requires, allowing patients to be more ambulatory. Outpatient therapy also has been studied.3 Treatment of venous thromboembolism with LMWH has been shown to be cost-effective, despite the higher price of LMWH.4 One question that remains unanswered, though, is what differences, if any, may be found in the efficacy and safety of the various LMWH preparations.

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Copyright © 2005 by the American Academy of Family Physicians.

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