Aims: This study constituted the first administration of the oral platelet inhibitor, sibrafiban, to humans. The aim was to investigate the pharmacokinetics and pharmacodynamics of Ro 44-3888, the active principle of sibrafiban, after single ascending oral doses of sibrafiban. Particular emphasis was placed on intersubject variability of the pharmacokinetic and pharmacodynamic parameters of Ro 44-3888.
Methods: The study consisted of three parts. Part I was an open ascending-dose study to determine target effect ranges of sibrafiban. Part II, a double-blind, placebo-controlled, parallel-group study, addressed the intersubject variability of pharmacokinetic and pharmacodynamic parameters of the active principle at a sibrafiban dose achieving an intermediate effect. Part III was a double-blind, placebo-controlled, ascending-dose design covering the complete plasma concentration vs pharmacodynamic response curve of sibrafiban.
Results: At sibrafiban doses between 5 mg and 12 mg, the pharmacokinetics of free Ro 44-3888 in plasma were linear whereas those of total Ro 44-3888 were non-linear because of the saturable binding to the glycoprotein IIb-IIIa receptor. Saturation of the GP IIb-IIIa receptor was reached at plasma concentrations of 15.9 ng ml-1. At sibrafiban doses up to 2 mg, ADP-induced platelet aggregation was inhibited by 50%, whereas the inhibition of TRAP-induced platelet aggregation was about 20-30%. At the higher doses, ADP-induced platelet aggregation was almost completely inhibited while a clear dose-response could be observed with TRAP-induced inhibition of platelet aggregation at sibrafiban doses of 5 to 12 mg. Ivy bleeding time increased very steeply with dose with a significant prolongation observed at doses of 5 to 7 mg of sibrafiban (5-7 min, >30 min in one case). At a sibrafiban dose of 12 mg, the stopping criterion for dose escalation (prolongation of the Ivy bleeding time >30 min in three out of four subjects per dose group) was reached. The interindividual coefficients of variation of the integrated pharmacokinetic and pharmacodynamic parameters (AUC and AUE) were below 20%, thus lying well within the pre-set level of acceptance.
Conclusions: With a low intersubject variability of its pharmacokinetic and pharmacodynamic parameters, linear pharmacokinetics and pharmacodynamic effects closely related to its plasma concentrations, Ro 44-3888 has good pharmacological prerequisites for a well controllable therapy of secondary prevention of arterial thrombosis in patients with acute coronary syndrome.