Amgen will pay $290 million to end its collaboration with British drugmaker GlaxoSmithKline to commercialize the osteoporosis drug denosumab in certain markets outside the U.S., it said April 3.

Thousand Oaks-based Amgen said it will take back marketing of denosumab in the European Union, Switzerland, Norway, Russia and Mexico. It will continue to let GSK market the drug — which is sold under the brand names Prolia and Xgeva — in Australia and as a treatment for conditions other than osteoporosis in countries such as China, South Korea, Brazil and India.

Prolia is one of Amgen’s fastest-growing drugs, with sales up 58 percent to $744 million last year.

In the agreement with GSK in 2009, Amgen retained the rights to market denosumab in the U.S. and Canada as a treatment for osteoporosis and other conditions and as a treatment for cancer in Europe, Australia, New Zealand and Mexico. The Thousand Oaks firm is testing denosumab as a possible treatment for cancer-related bone damage.

Amgen shares traded down 1.5 percent to $124.13 on the news.