April 28 (Reuters) - The U.S. Food and Drug Administration on Friday approved Radius Health Inc's drug to treat osteoporosis in postmenopausal women at high risk of fracture or those who have failed other therapies.

The drug, Tymlos, is given by injection and was shown in clinical trials to reduce the absolute risk of spine fractures by 3.6 percent compared with a placebo and to reduce the risk of non-spinal fractures by 2 percent.

The drug, which was approved earlier than expected, will compete with Eli Lilly & Co's Forteo and Amgen Inc's Prolia.

The company did not disclose a price of the drug but is expected to do so on a conference call with investors on Monday.

"This approval transforms Radius into a commercial-stage company," said Jessica Fye, an analyst with J.P. Morgan in a research note. "We believe that with healthy projected gross margins, they have room to price in line or even at a discount to Forteo."

Tymlos carries a boxed warning of the risk of bone cancer similar to one for Forteo.

Some analysts cautioned that Tymlos may face significant competitive challenges.

"While FDA approval is positive, we continue to see significant commercial hurdles as likely given competition," Jefferies analyst Eun Yang said in a research note.

He estimated the drug will generate peak annual sales of $450 million by 2028.

Radius's shares closed up roughly 1 percent at $39.07. (Reporting by Toni Clarke in Washington; Editing by Bill Trott)