Gabexate mesilate (FOY) and aprotinin. A comparative study of the effects on trypsin-induced activation of the kinin and complement systems in vivo and in vitro.

The effect of gabexate mesilate (FOY) was studied in vitro in human and canine serum upon the addition of trypsin, and in vivo in dogs during intravenous trypsin infusion. The effect of FOY was compared with the effect of aprotinin. FOY did not show any protection against trypsin-induced activation of the complement and kinin systems in vitro or in vivo, while aprotinin did. All dogs exhibited signs of circulatory shock together with a consumption of the two main proteinase inhibitors, alpha-macroglobulin and alpha 1-proteinase inhibitor, when intravenous infusions of FOY and trypsin were performed simultaneously. However, all dogs survived without signs of shock if aprotinin was given instead of FOY. The ineffectiveness of FOY in serum is explained by the complete dissociation of FOY trypsin complexes together with a rapid degradation of FOY to inactive metabolites. Although FOY is an effective proteinase inhibitor in defined buffer systems in vitro, the results of the present study indicate that it is not an effective proteinase inhibitor in vivo. Aprotinin protects against trypsin-induced activation reactions, although much higher concentrations are needed in human than in canine serum.