(Adds details, background, GSK statement)
April 3 (Reuters) - Amgen Inc said it would end an agreement with GlaxoSmithKline Plc for the marketing of its osteoporosis drug in some regions outside the United States.
Amgen said it would take over the marketing of the drug, sold under the brand name Prolia, in most areas under the agreement, including the European Union, Switzerland, Norway, Russia and Mexico, by Dec. 31.
GSK will continue to market the drug in Australia, Amgen said in a regulatory filing. (http://link.reuters.com/cax28v)
"GSK and Amgen have reached a mutual agreement to end their existing agreement...," a GSK spokesman said in an emailed statement, adding, "This new arrangement will allow GSK to increase focus on executing important new product launches over the next few years."
Amgen said it would pay GSK $275 million over the rest of the year and reimburse the British drugmaker $15 million for costs incurred during the transition period.
Prolia generated worldwide sales of $744 million in 2013, a 58 percent increase from a year earlier. (http://link.reuters.com/mux28v)
According to the agreement signed in July 2009, Amgen retained the rights to market the drug in the United States and Canada as a treatment for osteoporosis and other conditions and as a treatment for cancer in Europe, Australia, New Zealand and Mexico.
Amgen also said on Thursday that GSK would continue to market the drug as a treatment for conditions other than osteoporosis in countries such as China, Brazil, India and South Korea.
GSK holds the marketing rights in these regions until 2024, according to Amgen's annual report.
Amgen is developing the drug in late-stage studies as a treatment for other forms of osteoporosis, including glucocorticoid-induced osteoporosis and male osteoporosis.
The company is also testing the drug, denosumab, as a treatment for cancer-related bone damage.
Denosumab is sold under the brand name Prolia as a treatment for three conditions, including postmenopausal osteoporosis in women at high risk of fracture.
The drug is approved in the United States as a treatment for giant cell tumor of the bone and is sold under the brand name Xgeva.
(Reporting by Vrinda Manocha in Bangalore; Editing by Simon Jennings)