Determination, pharmacokinetics and protein binding of a novel tissue-typeplasminogen activator, pamiteplase in human plasma

1. An enzyme-linked immunosorbent assay (ELISA) and functional bioassay to determine immunoreactive and bioactive concentrations of pamiteplase, a nov el thrombolytic agent, in human plasma were developed. The ELISA and functi onal bioassay showed satisfactory accuracy and precision within a concentra tion range of 0.5-25 ng.ml(-1) and of 0.127-16.2 ng.ml(-1) respectively. 2. The pharmacokinetics of pamiteplase in healthy human subjects were evalu ated using the ELISA and functional bioassay. Irrespective of the method us ed, plasma concentrations declined bi-exponentially. Half-lives in the beta phase were 1.25 and 0.78 h, and AUCs were 507.9 and 286.4 ng.h.ml(-1) resp ectively. Total clearances of pamiteplase decreased to 19 and 31 % of those of the wild-type tissue-type plasminogen activator. 3. The protein binding of pamiteplase in human plasma was investigated by g el filtration chromatography. Pamiteplase formed three high molecular weigh t complexes with alpha (2)-macroglobulin, C-1-esterase inhibitor and alpha (2)-plasmin inhibitor in human plasma. This complex formation was relativel y slow, and was thought to be irreversible and covalently bounded. Furtherm ore, this protein binding in humans resulted in the termination of biologic al action.