Portola Pharmaceuticals has posted initial results from a Phase II proof-of-concept study of andexanet alfa, its investigational Factor Xa inhibitor antidote, in healthy volunteers who were administered the Factor Xa inhibitor Xarelto (rivaroxaban). Results from the first two dosing cohorts of the study demonstrated that andexanet alfa is able to dose-dependently reverse the anticoagulant effects of Xarelto, with no serious adverse events reported. These data, as well as data from additional coh...