U.S. biotechnology firm Amgen, the world's largest, is ending its  agreement with the U.K. drugmaker GlaxoSmithkline for the marketing of its osteoporosis drug in some regions outside the U.S..

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.

The world's largest biotechnology company said it would pay $275 million to GSK over the rest of this year and reimburse its partner $15 million for costs incurred during the transition period.

Prolia generated worldwide sales of $744 million in 2013, a 58% increase against 2012.

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 said GSK would continue to market Prolia 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.