Preclinical biochemistry and pharmacology of low molecular weight heparins in vivo - Studies of venous and arterial thrombosis

Low molecular weight heparins (LMWHs) are effective agents in both venous and arterial thrombosis. Extensive preclinical studies in various animal models show that there are substantial differences in antithrombotic efficacy between LMWHs, and that the relative efficacy of Individual agents depends on the thrombogenic stimulus used. Relative efficacy cannot be predicted on the basis of molecular weight, nor on the basis of anti-factor Xa or anti-factor IIa potency. This suggests that other mechanisms of action, e.g., the release of tissue factor pathway inhibitor (which differs among the LMWHs), are important. Data obtained with a specific LMWH cannot be extrapolated to other compounds within the same class and their substitution in the clinical setting is, therefore, inappropriate.