Measurements of ADP-induced ex vivo platelet aggregation at physiologic calcium concentrations (D-phenylalanyl-L- prolyl-L-arginine chloromethyl ketone [PPACK] anticoagulant) in patients presenting with unstable angina and Non Q-Wave Myocardial Infarction showed a concentration-dependent inhibition with an IC50 (50% inhibitory concentration) of approximately 550 ng/ ml and an IC80 (80% inhibitory concentration) of approximately 1,100 ng/ ml.