Portola Pharmaceuticals’ andexanet alfa significantly reversed the blood-thinning effects of a Factor Xa inhibitor in a late-stage trial, which hit all of primary and secondary targets.

The Phase III ANNEXA-A trial - which will form part of the drug’s US registration later this year - rapidly reversed the anticoagulant effect of Pfizer/Bristol-Myers Squibb’s Eliquis (apixaban) by 93.5%, and sustained a high level of efficacy across the two-hour infusion period.

Andexanet alfa significantly reduced the level of free unbound Eliquis in the plasma and restored thrombin generation to normal, while no serious adverse events were reported in the trial, the firm noted.

According to Portola, its drug has the potential to be a first-in-class antidote for anticoagulated patients who suffer a major bleeding episode (1%-4%) or those require emergency surgery (up to 1%), and could therefore offer an important new treatment option.

The firm said it plans to submit data from trial, as well as from and ANNEXA-R - which is testing the drug’s effect on Bayer’s clot buster Xarelto [rivaroxaban] - and early findings from a Phase IV study as part of its Biologics License Application to US regulators by the end of 2015.