Portola announces andexanet alfa, enoxaparin 'positive' Phase 2 data Portola Pharmaceuticals announced that a Phase 2 proof-of-concept study in healthy volunteers demonstrated that andexanet alfa immediately reversed the anticoagulation activity of enoxaparin. Andexanet alfa was well tolerated with no serious adverse events reported. Detailed data will be presented during both oral and poster sessions at the 60th Scientific and Standardization Committee Meeting of the International Society on Thrombosis and Haemostasis. Portola is developing andexanet alfa to reverse the anticoagulation activity of Factor Xa inhibitor-treated patients who are experiencing a major bleeding episode or who require emergency surgery. Andexanet alfa was well tolerated with no thrombotic events or serious adverse events reported. No antibodies to andexanet alfa, Factor Xa or Factor X were observed.