Are Low Molecular Weight Heparins the Same

Low molecular weight heparins (LMWHs) are glycosaminoglycans (GAGs) of different chain length, molecular weight distribution, and different physiochemical characteristics that result from their diverse methods of preparation, which make them non-interchangeable. The anticoagulant potency of heparin is measured as USP U/mg. This method is only applicable to LMWHs at high doses, when their anticoagulant properties are apparent. Anti-Xa activity has not enabled standardization of the biologic actions of LMWHs, since it does not address the ATIII-independent actions of LMWHs. Yet the European Pharmacopoeia Commission has adopted anti-Xa activity as a measure of LMWH potency. Since other markers of pharmacological activity also differ among LMWHs, their anti-IIa activity, tissue-factor pathway inhibitor (TFPI) releasing capacity, anti-inflammatory, and other cellular effects should be useful biomarkers in determining the biologic activity of each LMWH.