Low molecular weight heparins in the outpatient management of venous thromboembolism

Low molecular weight heparin (LMWH) has challenged the position of unfractionated heparin (UFH) as the treatment of choice in preventing progression, recurrence, and complications of venous thromboembolism (VTE). A meta-analysis of 13 randomized trials has shown that subcutaneous LMWH is associated with lower rates of recurrence, bleeding, and mortality than is intravenous UFH. The use of subcutaneous LMWH yields substantial savings in pharmacy and nursing costs. Recent trials have demonstrated that home treatment with enoxaparin and dalteparin is at least as safe and effective as inpatient treatment with UFH, is feasible in more than 70% of patients with VTE, and is associated with improved quality of life. Home treatment saves as much as $6000 per patient relative to inpatient treatment with UFH and nearly $3000 per patient relative to inpatient treatment with LMWH. Of the three LMWH preparations available in the United States, enoxaparin, dalteparin, and ardeparin, only enoxaparin is approved for the treatment of deep-vein thrombosis. These LMWHs differ substantially in molecular weight and molecular size distribution, bleeding indices in animal models, anti-Xa activity, anti-Xa/anti-IIa ratio, and release of tissue factor pathway inhibitor. Although the clinical relevance of these differences remains uncertain, the United States Food and Drug Administration recognizes LMWHs as distinct noninterchangeable drugs.