A laboratory method for parallel determination of platelet aggregation and thrombin generation

Optimal use of combinations of antiaggregating and antithrombotic drugs in vivo requires improved methods for testing of possible synergistic drug effects. Therefore, we developed an in vitro model that allows parallel evaluation of the influence of drugs on the time course of platelet aggregation inhibition and on thrombin generation inhibition. Platelet rich plasma samples were incubated with different amounts of antiaggregating and/or antithrombotic agents and the effects on thrombin generation, lag phase until the onset of platelet aggregation, and on inhibition of platelet aggregation were detected. Plasma activation was performed by addition of high (29 nM final concentration, "high coagulant challenge") or low (5 pM final concentration, "low coagulant challenge") amounts of tissue factor. Thus, platelet activation is initiated in our model by endogenously generated thrombin and not by exogenously added agonists, as usual in conventional evaluation of platelet aggregation. The combination of glycoprotein IIb/IIIa inhibitors (eptifibatide or abciximab) and anticoagulants (unfractionated heparin, low molecular weight heparin, or recombinant hirudin) used in this study exhibited an additive effect on prolongation of the lag phase until the onset of platelet aggregation. Under high but not under low coagulant challenge the combination of eptifibatide and anticoagulants had a synergistic inhibitory effect on platelet aggregation. Combination of abciximab and anticoagulants had no additive inhibitory effects on platelet aggregation under both high and low coagulant challenge. Under low coagulant challenge combination of eptifibatide but not abciximab with low molecular weight heparin significantly reduced the thrombin generation. We suggest that our laboratory method might be useful for pre-clinical testing of in vitro effects of glycoprotein IIb/IIIa inhibitors and anticoagulants.