UPDATE 1-Amgen says denosumab vs Fosamax trial meets goals

(Adds background, company comments)

LOS ANGELES Jan 24 (Reuters) - Amgen Inc (AMGN.O) said on Thursday that a head-to-head trial comparing its experimental osteoporosis drug denosumab to Merck & Co Inc's (MRK.N) Fosamax in post-menopausal women with low bone mineral density met all of its goals.

Amgen said the one-year study involving just over 1,000 patients showed that the relative magnitude of bone mineral density improvement at the hip was about 40 percent greater in patients injected with denosumab, compared with the group treated with oral Fosamax.

The company also said the study showed similar side effects, including infection rates, for both arms of the trial.

"The rate of serious adverse events was completely balanced," said Roger Perlmutter, head of research and development at Thousand Oaks, California-based Amgen.

The results are seen as key to denosumab's market potential, since lower-priced generic versions of Fosamax, also known as alendronate, are expected to be available before the Amgen drug is launched.

Still, data from a pivotal-stage trial designed to measure the ability of denosumab to reduce bone fractures is not expected until the second half of this year.

"We would expect a lot more safety information from that trial," which is a three-year study involving around 8,000 patients, Perlmutter said.

(Reporting by Deena Beasley, editing by Phil Berlowitz, Richard Chang)