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

Abstract

1. An enzyme-linked immunosorbent assay (ELISA) and functional bioassay to determine immunoreactive and bioactive concentrations of pamiteplase, a novel thrombolytic agent, in human plasma were developed. The ELISA and functional bioassay showed satisfactory accuracy and precision within a concentration 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 evaluated using the ELISA and functional bioassay. Irrespective of the method used, plasma concentrations declined bi-exponentially. Half-lives in the β phase were 1.25 and 0.78 h, and AUCs were 507.9 and 286.4 ng.h.ml⁻¹ respectively. 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 gel filtration chromatography. Pamiteplase formed three high molecular weight complexes with α₂-macroglobulin, C₁-esterase inhibitor and α₂-plasmin inhibitor in human plasma. This complex formation was relatively slow, and was thought to be irreversible and covalently bounded. Furthermore, this protein binding in humans resulted in the termination of biological action.