Bayer and Johnson & Johnson unit Janssen Pharmaceuticals have signed a pact with Portola Pharmaceuticals to investigate the potential of the latter's PRT4445 as an antidote to Factor Xa inhibitor blood thinners.

The companies have agreed to work together to test the safety of the novel recombinant protein PRT4445 in healthy volunteers given the oral bloodthinner Xarelto (rivaroxaban), after Phase I trial found the drug to be "generally well tolerated with no apparent safety signals", according to the firms. 

The Phase II study, completion of which is anticipated during the second half of this year, will assess multiple dosage strengths of PRT4445, to determine the dose needed to reverse the anticoagulant activity of Xarelto in emergency situations.

Clinical trial results indicate that between 1%-4% of patients treated with Factor Xa inhibitors will experience uncontrolled bleeding a year, and an additional 1% will need emergency surgery, depending on underlying health.

Explaining the rationale behind the move, Kemal Malik, Member of the Bayer HealthCare Executive Committee and Head of Global Development, said that while merely stopping the intake of Xarelto is usually enough to normalise blood clotting in itself, "we understand the desire of doctors to have a specific antidote to reverse the anticoagulation effects of the product…[and]… are addressing this request both through in-house research as well as through this external collaboration with Portola".

Under the terms of the deal, Bayer and Janssen will make an undisclosed payment to Portola, as well as provide regulatory and development guidance for the study. Portola will hold onto all its development and commercialisation rights to the drug.

PRT4445 is currently the only universal Factor Xa inhibitor antidote in clinical development, according to Portola.