Letters Section Editor: Robert M. Golub,
MD, Senior Editor.
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.
Arbit E. Fractionating Heparin. JAMA. 2004;292(12):1427-1428. doi:10.1001/jama.292.12.1427-b