Thrombin???hirudin complex stability; a comparison with the thrombin???antithrombin III complex

In the present in vitro study the stabilities of the thrombin-hirudin and the thrombin-antithrombin III complexes were investigated. After incubation of the complexes with free inhibitors the thrombin-antithrombin III levels were determined by ELISA. The thrombin-hirudin complex proved to be stable in the presence of antithrombin III or heparin. However, in the presence of heparin and plasma equivalent concentrations of antithrombin III, the thrombin-hirudin complex dissociated and hirudin was displaced. In contrast, both thrombin-antithrombin III and thrombin-antithrombin III/heparin complexes are very stable even in the presence of a large excess of hirudin.