Janssen Pharmaceuticals has signed a clinical collaboration agreement with Portola Pharmaceuticals and Bayer HealthCare to evaluate the safety of PRT4445—an investigational-stage antidote for Factor Xa inhibitors—in healthy volunteers who have been administered the oral anticoagulant Xarelto (rivaroxaban). The study will evaluate several dosage strengths of PRT4445 and its ability to reverse the anticoagulant activity of Xarelto in emergency situations.

As part of the agreement, Janssen and Bayer will make an upfront payment to Portola and will provide development and regulatory guidance for the study. Portola retains full global development and commercialization rights for PRT4445.

Xarelto is approved by the FDA for six distinct uses. This proof-of-concept study is scheduled to complete in the second half of 2013. A phase III trial will be required prior to submitting PRT4445 to the FDA for approval in this setting. Standard clinical measures are currently employed to manage these patients and events.

"Xarelto has the broadest indication profile of any of the new oral anticoagulants in the U.S. market, and is being used by a wide array of patients in many different settings," said Larry E. Fields, M.D., senior director, clinical development, medical affairs, Janssen. "We are committed to exploring ways to expedite reversal of the drug's effects when necessary, which could provide physicians with an additional treatment option during emergency situations."