Merck & Co has surprised some observers by returning the global rights to Portola Pharmaceuticals for the investigational clotbuster betrixaban.

Betrixaban is an oral Factor Xa inhibitor anticoagulant being evaluated for the prevention of stroke in patients with atrial fibrillation. In July 2009, Merck and Portola announced a collaboration for the drug that could have been worth $470 million (plus royalties) to the latter firm, and the US giant made an upfront payment of $50 million.

Most recently, betrixaban completed the Phase II EXPLORE-Xa trial in which it showed dose dependent clinical activity with similar or lower rates of bleeding compared to warfarin. Luciano Rossetti, head of global scientific strategy at Merck, noted that "working closely with our Portola collaborators we have advanced betrixaban to this Phase III-ready stage".

However the rights have been returned, "as part of an ongoing prioritisation of our late-stage pipeline", though he stressed that Merck "remains committed to delivering medicines for cardiovascular disease".

The decision comes just a few months after a briefing in London, when Daniel Bloomfield, head of clinical and translational medicine, cardiovascular, at Merck Research Laboratories, told PharmaTimes World News that he believed betrixaban would be able to hold its own in the highly-competitive stroke market. He said the drug would not have too much ground to make up on Boehringer Ingelheim's factor Xa inhibitor Pradaxa (dabigatran), which was approved by the US Food and Drug Administration for stroke risk reduction in non-valvular AF in October 2010.

As for Portola, chief executive William Lis said regaining the rights "represents a transformational opportunity" for the Californian firm. He added that "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".

Zostavax label expanded

In other Merck news, the FDA expanded approval of Merck's shingles vaccine Zostavax to include adults aged 50 to 59. The herpes zoster vaccine is already available for  patients aged 60 years and older.

The label change is based on data from a clinical study involving 22,000 patients aged 50 to 59. It showed that  Zostavax reduced the risk of shingles by nearly 70%.

The expanded indication "is important for the health of people who are 50 and older because nearly everyone in that age group is at risk for developing shingles," said Jeffrey Silber, vice president, Merck Research Laboratories. According to the US Centers for Disease Control and Prevention, one in three people across the Atlantic will experience shingles in their lifetime and nearly one million cases occur each year.

Julie Gerberding, head of Merck Vaccines, noted that the company is "investing more than $1 billion to enhance manufacturing so that as many people as possible may have access to Zostavax and our other varicella-containing vaccines".