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To the Editor: In their Editorial, Drs Das and Moliterno¹ note several known limitations of unfractionated heparin, including a narrow therapeutic window, poorly predictable kinetics, platelet activation, and inability to inhibit clot-bound thrombin. They state that enoxaparin has a higher anti-factor Xa–anti-factor IIa ratio, which reduces some of these limitations. Both anti-factor Xa and anti-factor IIa are independently important attributes in thrombosis: anti-Xa for prevention of thrombin generation and anti-IIa for therapy. I am not aware of any data to suggest that the ratio adds meaningful information with respect to benefits or risk reduction related to bleeding. The advantages of low-molecular-weight heparins relate to their predictable pharmacokinetics and the convenience of being able to administer the drug subcutaneously in an outpatient setting without the need for monitoring activated partial thromboplastin time.

Ehud Arbit, MD
earbit@emisphere.com
Emisphere Technologies Inc
Tarrytown, NY

1. Das P, Moliterno DJ. Fractionating heparins and their clinical trial data: something for everyone. JAMA. 2004;292:101-103. FREE FULL TEXT

Letters Section Editor: Robert M. Golub, MD, Senior Editor.

JAMA. 2004;292:1427.

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Fractionating Heparin—Reply
Pranab Das and David J. Moliterno
JAMA. 2004;292(12):1427-1428.
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