Background: The pharmacological effect of rFVIIa occurs at the surface of activated platelets by enhancing thrombin generation at the site of vascular damage. It is therefore important to study the effects of rFVIIa in platelet-related bleeding situations. We examined the effect of rFVIIa and an rFVIIa-analogue, NN1731, on clopidogrel-induced and thrombocytopenic bleeding in rats.
Methods and results: Clopidogrel [10 mg kg(-1); per oral (p.o.)] severely inhibited platelet aggregation and increased blood loss after tail-transection four hours after administration. Treatment with rFVIIa (5, 10, 20 mg kg(-1)) or NN1731 (1, 5, 10 mg kg(-1)), administered five minutes after induction of bleeding, reduced blood loss significantly and dose-dependently. NN1731 had an increased hemostatic potential compared with rFVIIa, reducing blood loss to the control level, whereas this was not even achieved with the highest dose of rFVIIa. Antibody-induced thrombocytopenia reduced platelet numbers by more than 90% and increased the blood loss after tail-transection. Treatment with 10 and 20 mg kg(-1) rFVIIa significantly reduced blood loss, whereas 10 mg kg(-1) NN1731 reduced the bleeding to control levels.
Conclusions: The hemostatic effect of rFVIIa and NN1731 was demonstrated in thrombocytopenic and clopidogrel-treated rats, showing efficacy in situations with decreased platelet number or functionality. Our findings are consistent with the hypothesis that rFVIIa/NN1731 contribute to hemostasis by thrombin generation even in situations with platelet disorders. Furthermore, NN1731 demonstrated a higher hemostatic potential than rFVIIa.