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September 22/29, 2004

Fractionating Heparin

Author Affiliations

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

JAMA. 2004;292(12):1427-1428. doi:10.1001/jama.292.12.1427-b

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.

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