The protective dose of the potent GPIIb/IIIa antagonist SC-54701A is reduced when used in combination with aspirin and heparin in a canine model of coronary artery thrombosis

Fibrinogen receptor antagonists block the fibrinogen-platelet interaction at the GPIIb/IIIa receptors and inhibit thrombus formation. SC-54701 is the active metabolite of SC-54684A, an orally fibrinogen receptor antagonist. We compared the efficacy of SC-54701A (SCa, hydrochloride salt) with that of aspirin (ASA) or heparin and with combination therapy in a canine model of continuous current injury. Sixty-six dogs were used (6 per treatment). SCa (15-minute loading dose followed by [//] infusion [microgram/kg per minute]: (0.87//0.39=1 X SCa; 0.52//0.23=0.6 X SCa; and 0.425//0.20= 0.5 X SCa), ASA (2.8 mg/kg), heparin (200 U/kg plus 1000 U/h), or saline (0.1 mL/kg) was administered intravenously. Experimental time was 180 minutes of current. Time to occlusion was increased (P < .05) by SCa (T=incidence of thrombosis) (1 X SCa, >180 minutes [T=0]; 0.6 X SCa, 158 +/- 15 minutes [T=2]; 0.5 X SCa, 130 +/- 22 minutes [T=4]), heparin (114 +/- 16 minutes [T=5]), and ASA plus heparin (130 +/- 11 minutes [T=5]) relative to saline (58 +/- 7 minutes [T=6]). Time to occlusion for the SCa treatments was increased compared with ASA (64 +/- 7 minutes [T=6]). When 0.5 X SCa was administered with ASA plus heparin, time to occlusion was >180 minutes [T=0]. SCa provided complete protection at > or = 90% inhibition of ex vivo collagen-induced platelet aggregation. Cyclic flow variations were minimal with SCa or any treatment involving 0.5 X SCa and ASA. SCa has dose-dependent antithrombotic efficacy and inhibits ex vivo platelet aggregation. ASA, heparin, or saline was ineffective in this model. SCa (0.5X) plus ASA and heparin maximized the antithrombotic effect of this lower dose of SCa.