Portola Pharmaceuticals and Merck known as MSD outside the United States and Canada, today announced that Merck
plans to return to Portola all rights for betrixaban, an investigational oral
Factor Xa inhibitor anticoagulant being evaluated for the prevention of stroke
in patients with atrial fibrillation (SPAF). This decision was made following a
review of Merck’s investigational portfolio.

“Regaining full rights to betrixaban represents a
transformational opportunity for Portola,” said William Lis, chief
executive officer of Portola. “We will work with our academic partners on
options for an independent development plan to bring betrixaban to the market
and intend to discuss these options with the FDA in the near future.” In
July 2009, Merck and Portola announced an exclusive global collaboration and
license agreement for the development and commercialization of betrixaban.
Betrixaban most recently completed Phase II testing in the EXPLORE-Xa trial in
which it showed dose dependent clinical activity with similar or lower rates of
bleeding compared to warfarin in the study population. These results were presented
during a late-breaking clinical trials session at the American College
of Cardiology’s 59th Annual Scientific Session in March 2010.

“Working closely with our Portola collaborators we have
advanced betrixaban to this Phase III-ready stage,” said Luciano Rossetti,
M.D., senior vice president, Global Scientific Strategy at Merck. “As part
of an ongoing prioritization of our late-stage pipeline, we have decided to
return rights for betrixaban to Portola. Merck continues to advance its broad
late-stage pipeline and remains committed to delivering medicines for
cardiovascular disease.”