Inhibition of ex-vivo PAF-induced platelet aggregation by the PAF-antagonist RP 48740: relationship to plasma concentrations in healthy volunteers.

RP 48740, 3-(3-pyridyl)-1H,3H-pyrrolo [1,2-c] thiazole-7-carboxamide, a specific competitive PAF-receptor antagonist in vitro, was given to 29 healthy male volunteers for 7 days. Plasma drug concentrations and ex-vivo PAF-induced platelet aggregation were assessed on Days 1, 4, and 7. RP 48740 had linear pharmacokinetics after single and repeated doses. It caused stable inhibition of PAF-induced platelet aggregation in a dose-dependent manner. The effect disappeared within 24 h, even after 7 days of repeated doses. The effect of RP 48740 displayed a sigmoidal relation to the plasma drug concentration; I50 2.3 (0.3) mg.l-1. There were no clinical or biological adverse reactions to RP 48740 during the study.