Enoxaparin vs. Heparin: The PREVAIL Study

The jury is still out but may favor enoxaparin.

In this manufacturer-sponsored, open-label, international trial, researchers compared the effectiveness and safety of enoxaparin (low-molecular-weight heparin) and of unfractionated heparin in reducing the overall number of venous-thromboembolism (VTE) events after acute ischemic stroke. The authors randomized 1762 patients within 48 hours of an acute ischemic stroke to receive either enoxaparin (40 mg once daily) or unfractionated heparin (5000 U every 12 hours) for a mean of 10 days. Patients underwent ultrasound, venography, or both. Pulmonary embolism, if suspected, was evaluated by ventilation perfusion scan, helical CT, or angiography.

The analysis included 76% of the patients. Compared with unfractionated heparin, enoxaparin conferred a 43% reduction in overall number of VTE events up to day 14 that was maintained at 30, 60, and 90 days and was independent of stroke severity (NIHSS score of <14 vs. 14). However, the number of symptomatic VTE events did not differ between the treatment groups, and mortality rates were similar. The number of intracranial bleeding events was similar in both groups, and extracranial events (mainly gastrointestinal bleeding) were slightly more common in the enoxaparin group.

Comment: This was the largest prospective study of its kind. Despite some limitations, this study’s many strengths include its strong statistical power and long-term follow-up. The findings may justify the routine use of enoxaparin, although cost was not addressed and the number of symptomatic events was similar regardless of treatment. These limitations indicate that a more thorough cost-effectiveness analysis is needed before enoxaparin is adopted as the standard of care.

— Flavia Nelson, MD, and James Grotta, MD

Dr. Nelson is Assistant Professor of Neurology, Board Certified Internist, The University of Texas Houston Medical School, and Assistant Director, MRI Analysis Center, Multiple Sclerosis Research Group, The University of Texas Health Science Center at Houston. Dr. Grotta is Professor and Chair, Department of Neurology, The University of Texas Houston Medical School, and Director of Vascular Neurology, The University of Texas Health Science Center at Houston.

Published in Journal Watch Neurology June 26, 2007

Citation(s):
Sherman DG et al. The efficacy and safety of enoxaparin versus unfractionated heparin for the prevention of venous thromboembolism after acute ischaemic stroke (PREVAIL Study): An open-label randomised comparison. Lancet 2007 Apr 21; 369:1347-55.