The antithrombotic efficacy of the GP IIb/IIIa antagonist SR121787 is potentiated by antithrombin-dependent factor Xa inhibition without an increase in the bleeding risk in the rabbit

Current antithrombotic therapy in acute coronary symptoms is only partially effective and exhibits bleeding complications. These experiments were designed to address the antithrombotic and hemorrhagic interactions of the novel glycoprotein (GP) IIb/IIIa antagonist SR121787 in combination with the indirect inhibitor of factor Xa, SR90107/ORG31540. Thrombogenesis was initiated by electrolytic injury of the intimal surface of the carotid artery, and thrombus formation was assessed by recording carotid blood flow and by measuring thrombus weight 45 min after electrical stimulation. SR121787 was an efficacious antithrombotic agent in this model (ED50 = 16.3+/-0.3 mg/kg, p.o.), whereas heparin (4.5 mg/kg, i.v.) and SR90107/ORG31540 [1 mg/kg (850 aXa anti-units/kg), i.v.] were only marginally effective (17 and 27% inhibition of carotid blood flow reduction, respectively). Coadministrations of heparin (4.5 mg/kg, i.v.) or SR90107/ORG31540 (0.5 mg/kg, i.v.) were found to potentiate the antithrombotic efficacy of threshold doses of SR121787 (5 or 10 mg/kg, p.o.). The enhancement of the antithrombotic efficacy of SR121787 by SR90107/ORG31540 was--contrary to the association of SR121787 with heparin--not accompanied by an increased blood loss from the incised rabbit ear. Coadministrations of heparin or SR90107/ORG31540 did not influence the ex vivo antiaggregatory activity of SR121787. SR121787 coadministration did not alter the systemic anticoagulant activities in heparin or SR90107/ORG31540-treated animals. These data suggest the potential for optimized antithrombotic treatment in acute coronary syndromes when a GP IIb/IIIa antagonist (SR121787) is combined with an antithrombin-dependent factor Xa inhibitor (SR90107/ORG31540).