Active site-inactivated factor VIIa prevents thrombosis without increased surgical bleeding: topical and intravenous administration in a rat model of deep arterial injury.

PURPOSE: The primary event in the procoagulant response after vascular interventions is the tissue factor (TF)-factor VIIa complex formation, which occurs when TF is exposed to the circulating blood by the inflicted trauma. Human recombinant active site-inhibited coagulation factor VIIa (FFR-rFVIIa) binds well to TF but cannot initiate blood coagulation, and should thereby block thrombus formation. This hypothesis was tested with a rat model of arterial thrombosis.
METHODS: In a blinded randomized study, the antithrombotic and antihemostatic effects of FFR-rFVIIa and heparin were evaluated in a rat model of mechanical deep arterial injury. In one arm of the study, FFR-rFVIIa (0.2 mg in 150 microL) or vehicle alone was applied topically at the site of vascular injury. In the other arm, FFR-rFVIIa (4 mg/kg), heparin (1 mg/kg), or vehicle alone was injected intravenously.
RESULTS: FFR-rFVIIa produced a powerful antithrombotic effect after both topical and intravenous administrations (P =.02 and P =.005, respectively) without increasing the surgical bleeding. Heparin prevented thrombosis equally well as FFR-rFVIIa (P =.0007), but doubled the surgical bleeding compared with FFR-rFVIIa (P =.03) and controls (P =.008). In the topical study, the antithrombotic effect was achieved without altering parameters of plasma anticoagulation (prothrombin time and activated partial thromboplastin time) or producing detectable levels of FFR-rFVIIa in plasma.
CONCLUSION: In this model FFR-rFVIIa effectively inhibits thrombus formation without the expense of increased surgical bleeding, which indicates the potential of FFR-rFVIIa as an effective and safe strategy for prevention of thrombosis in reconstructive vascular surgery and various forms of percutaneous revascularization.