Abstract 212: Andexanet Alfa, a Universal Antidote for Reversal of Anticoagulation of Factor Xa Inhibitors in Healthy Human Volunteers

Introduction: Andexanet alfa (AnXa) is a recombinant modified fXa molecule that acts as a specific antidote for fXa inhibitors. We report clinical results in healthy subjects anticoagulated with apixaban (apix), rivaroxaban (riva), edoxaban (edox), or enoxaparin (enox), demonstrating rapid and sustained reversal of anticoagulation following administration of AnXa. Methods: These were Phase 2/3 randomized, double-blind, placebo-controlled studies in healthy subjects. In Phase 2, about153 subjects age18 - 45 were given one of the fXa inhibitors (apix 5 mg BID, riva 20 mg QD, edox 60 mg QD or enox 40 mg QD) for 6 days. AnXa or placebo (3:1 randomization) was given IV on Day 6, 3hrs after the last inhibitor dose (∼inhibitor Cmax). Safety was followed through Day 48. A range of AnXa doses (bolus or bolus+infusion) was evaluated by correction of biomarkers (anti-fXa activity, free inhibitor concentrations and thrombin generation (TG)). In Phase 3 (ANNEXA™), older subjects age 50 to 75 were dosed with apix (5 mg BID) or riva (20 mg QD) for 4 days. ANNEXA™-A had 63 subjects treated with apix. AnXa (400 mg bolus; 400 mg bolus plus 4 mg/min x 2hr infusion) or placebo (3:1 randomization) was given on Day 4, 3 hrs after the last apix dose. ANNEXA™-R had 82 subjects treated with riva. AnXa (800 mg bolus; 800 mg bolus plus 8 mg/min x 2hr infusion) or placebo (2:1) was given on Day 4, 4 hrs after the last riva dose. Safety was followed through Day 43. Results: About 298 healthy subjects were enrolled in the studies. AnXa demonstrated rapid and sustained reversal of both direct and indirect fXa inhibitors as measured by correction of biomarkers. The ANNEXA™ studies confirmed findings from Phase 2, and met all primary (reversal of anti-fXa) and secondary endpoints (reduction of free inhibitor concentration and restoration of TG) with high statistical significance. AnXa was well-tolerated with no serious adverse events, thrombotic events, or antibodies to fX or fXa reported. Conclusion: AnXa treatment results in rapid and sustained reversal of anticoagulation of fXa inhibitors. A Phase 3b/4 confirmatory study (ANNEXA-4) in patients with acute major bleeds is ongoing.