Factor Xa and prothrombin: Mechanism of action of FEIBA

A complex consisting of-activated factor X (FX) (enzyme) and prothrombin (s ubstrate), both highly purified from human plasma and virus inactivated, wa s formulated, characterised biochemically as well as in animal studies, and given the name Partial Prothrombinase (PPT). In vitro, PPT shortened the c lotting time of a high-titre human factor VIII (FVIII) inhibitor plasma in a manner similar to that of the activated prothrombin complex concentrate F EIBA and triggered coagulation in plasma samples in which factor V (FV) is present. In vivo, the ability of PPT to activate coagulation in both chimpa nzees and baboons was equivalent to that of FEIBA. PPT also triggered coagu lation in a von Willebrand factor(vWf)-deficient dog and controlled bleedin g in rabbits with antibody-induced haemophilia A. Thus, studying the mechan ism of action of PPT also explains the therapeutic principle of FEIBA.