In the blood coagulation process, prothrombin is proteolytically cleaved to form thrombin (factor IIa) which in turn, acts as a serine protease that converts soluble fibrinogen into insoluble strands of fibrin. Specifically, thrombin converts factor XI to XIa, factor VIII to VIIIa, factor V to Va, fibrinogen to fibrin, and factor XIII to XIIIa. Direct thrombin inhibitors (DTIs) represent a new class
of promising anticoagulation agents. DTIs are increasingly
being used instead of heparin to provide initial,
rapid anticoagulation. Unlike heparin, which requires a mediator (antithrombin) to potentiate anticoagulation, Peptide DTIs can inhibit free and bound thrombin directly. Lepirudin (brand name Refludan) is a recombinant hirudin derived from yeast cells (Weitz et al. 1990). Hirudin is a naturally occurring anticoagulant produced by the salivary glands of medicinal leeches. Bivalirudin (brand name Angiomax, Angiox) is a synthetic analog of hirudin, with a shorter period of binding to thrombin (Gladwell 2002). Desirudin (brand name Iprivask) is another recombinant hirudin derivative that directly inhibits free and fibrin-bound thrombin (Graetz et al. 2011).