Amgen, GSK part on fast-selling Prolia, mostly

GlaxoSmithKline ($GSK) and Amgen ($AMGN) are parting ways on Prolia, their comarketed osteoporosis med that's been among the fastest-growing products approved in the last few years. Amgen will take over the task in most areas under their agreement, leaving GSK freer to buckle down on some new launches of its own.

According to a regulatory filing, Amgen will assume full marketing duties in areas including the EU, Switzerland, Norway, Russia and Mexico by Dec. 31. GSK retains rights in Australia to hock the drug for the bone condition and in countries such as China, Brazil, India and South Korea to sell it for other uses. The British pharma will say farewell to the £51 million ($84.6 million) in yearly Prolia sales, but in return, Amgen will fork over an initial payment and milestones tallying $275 million, with an extra $15 million in transition costs.

As a Glaxo spokesman told Reuters, the decision to terminate the marketing pact was mutual, and the new arrangement "will allow GSK to increase focus on executing important new product launches over the next few years."

Those new product launches are key for Glaxo, which currently derives close to 20% of its sales from aging asthma blockbuster Advair. While the drug's tricky inhaler technology has so far confounded generics makers, its hold on the market is slipping in both the U.S. and Europe.

Luckily for Glaxo, it has a host of new products ready to step in--and with giant shoes to fill, the company will need their launches to be as successful as possible. The drugmaker is currently readying for the U.S. launch of another potential respiratory star in chronic obstructive pulmonary disease (COPD) treatment Anoro, one of 6 GSK products to score the FDA's approval in 2013. At its peak, analysts expect Anoro to rake in $1.4 billion. But though that tally would help it crack the blockbuster barrier, it still pales in comparison with Advair's $8.25 billion haul.

As for Amgen, the new marketing territory will help it build on $744 million in 2013 Prolia sales, up 58% over 2012's total. The California-based biotech had been looking to the drug--sold in the U.S. as a therapy for giant cell tumor of the bone under the brand name Xgeva--to step in as sales of other products like anemia drug Epogen waned. But it's $10.4 billion pickup of Onyx Pharmaceuticals took some of the pressure off, adding quick-selling multiple myeloma med Kyprolis to the mix.

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