Comparative pharmacology of site directed antithrombin agents. Implication in drug development

Beside the direct inhibition of thrombin and its regulatory functions, many of the newer antithrombin agents produce several additional effects, unrelated to their anticoagulant actions. Synthetic peptide inhibitors are capable of producing fibrinolytic compromise by virtue of their actions on fibrinolytic enzymes such as t-PA, plasmin, urokinase and protein Ca. In addition, the low molecular weight arginine-containing peptides are also known to produce hemodynamic and hemostatic deficits. The designs of the ongoing clinical trials are largely empirical because of the non-availability of valid pharmacologic and toxicologic data on thrombin inhibitors. In contrast to heparin, none of the thrombin inhibitors produce endogenous release of tissue factor pathway inhibitor (TFPI) in the experimental and clinical settings. These observations suggest that beside the direct inhibition of thrombin, these agents also produce multiple additional effects that can significantly contribute to their pharmacologic and toxicologic profile.