Rapid and Simple Platelet Function Assay to Assess Glycoprotein IIb/IIIa Receptor Blockade

Background The platelet glycoprotein (GP) IIb/IIIa receptor antagonist c7E3 Fab (abciximab; ReoPro) has been approved as an antithrombotic agent, and other GP IIb/IIIa antagonists, including oral agents, are under development. At present, there are no rapid and simple assays to monitor GP IIb/IIIa receptor blockade. Methods and Results An assay was devised based on the ability of platelets in whole blood to rapidly agglutinate fibrinogen-coated beads when stimulated with a peptide, (iso-S)FLLRN, that activates a platelet thrombin receptor but resists inactivation by plasma aminopeptidase M. Preincubation of normal blood with increasing concentrations of c7E3 Fab led to increasing inhibition of the assay, correlating with increased GP IIb/IIIa receptor blockade. Assay conditions were chosen so that agglutination was inhibited at 2 minutes when >82% of the receptors were blocked. Similar results were obtained with the use of GP IIb/IIIa antagonists based on the arginine-glycine-aspartic acid (RGD) cell-reco...