Saturday, May 26, 2007

Is low molecular weight heparin better than unfractionated heparin for VTE prophylaxis?

The best regimen for VTE prophylaxis is controversial. Some recent research helps clarify but does not completely settle the controversy. This study in Thrombosis Journal evaluated outcomes in patients with a variety of medical conditions who received VTE prophylaxis with either the low molecular weight heparin (LMWH) enoxaparin versus unfractionated heparin (UH). There was a markedly reduced incidence of VTE in the enoxaparin group with no difference in adverse effects. The study received support from Aventis Pharmaceuticals, makers of enoxaparin. A potential weakness in this retrospective study is the lack of control over the doses of UH and LMWH. On the other hand it reflects real world use of the agents.

Then there was this prospective randomized open label study of enoxaparin versus UH for VTE prophylaxis in post-stroke patients presented at the American Stroke Association last February, showing a lower rate of VTE with enoxaparin and no difference in bleeding rates. This study, entitled Prevention of VTE After Acute Ischemic Stroke with Low-Molecular-Weight-Heparin Enoxaparin (PREVAIL), was also sponsored by Aventis. One weakness of this study, some might argue, is that it set up a straw man by testing enoxaparin against what some experts assume to be a less than optimal dose of UH (5000 units bid). However, this recent meta-analysis in Chest questions that assumption in that, in medical patients, the higher dose of UF, 5000 units tid, was no better than bid despite a higher bleeding rate.

Although the issue remains controversial, recent data suggest superiority of LMWH over UH for VTE prophylaxis in a variety of settings.

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