An experimental treatment for bone-thinning osteoporosis appears to prevent spine and hip fractures even though it is given only once a year, eliminating the need for a strict daily pill regimen, preliminary data show.

Reclast, given as an annual, 15-minute infusion, reduced risk of new spine fractures by 70 percent and of hip fractures by 40 percent, according to data supplied by maker Novartis Pharmaceuticals Corp. The drug, chemically known as zoledronic acid, also reduced the risk of fractures elsewhere, according to a just-completed, international study of 7,736 postmenopausal women with osteoporosis.

Side effects were generally minor and short-lived, said Novartis, of East Hanover, N.J.

The data, from final-stage human testing, was to be presented Saturday at the annual meeting of the American Society of Bone and Mineral Research in Philadelphia.

"This is very good news," said Dr. Ethel Siris, president of the National Osteoporosis Foundation and director of the Osteoporosis Center at Columbia University.

"Because it can be given once a year, it's going to be terrific for women who like that option," said Siris, who has consulted for Novartis and other drug companies.

Novartis plans to apply for U.S. approval to sell Reclast early next year.

Lead researcher Dennis Black, a professor of epidemiology at University of California-San Francisco, said that like Fosamax and other pills, Reclast slows down the speed at which cells called osteoclasts break down bone while other cells build it back up.

"If you take Fosamax every week for a year, you'll get a similar effect on bone density," Black said.

He noted that Reclast is part of a decade-long trend of researchers developing osteoporosis drugs taken less and less frequently: Some pills are taken only once a month, and one drug is available as a shot every three months.

Dr. Thomas Cavalieri, director of the New Jersey Institute for Successful Aging, said Reclast will be very significant, if approved, because many osteoporosis patients stop taking their medicine in the first year. One reason is that the pills can cause irritation and ulcers in the esophagus; to limit that, people must take them first thing on an empty stomach, with a large glass of water, then stay upright for 30 to 60 minutes.

That could make nursing home residents and patients with acid reflux disease, among others, good candidates for the shot.

In the United States, about 10 million people have osteoporosis and 34 million others have low bone density, putting them at risk for it, according to the National Osteoporosis Foundation. Half of women over age 50 with the disorder will suffer a fracture, which can trigger overall health decline and premature death.

Roughly one-third of the people with osteoporotic fractures don't know it, but as their vertebrae crack and compress they stoop forward, lose height and can suffer pain.

Treatment -- when the fracture is caught -- focuses on medicines to relieve pain, hot or cold packs, physical therapy and steps to prevent another fracture. Those steps include taking an osteoporosis drug and increasing calcium and vitamin D intake, either through diet or supplements.

For women entering menopause, it's better to try to prevent fractures by using those steps, weight-bearing exercise and getting bone density screenings.

Reclast is in the same category of osteoporosis drugs, bisphosphonates, as Fosamax from Merck & Co. of Whitehouse Station, N.J.; Actonel by Procter & Gamble Pharmaceuticals of Cincinnati and Boniva from Hoffmann-La Roche Inc. of Nutley, N.J. Another drug, Forteo from Eli Lilly & Co. of Indianapolis, is a form of human parathyroid hormone and must be injected in the thigh or abdomen daily.

Competition is so fierce that P&G unsuccessfully sued Hoffmann-La Roche over claims in its advertising campaign that Boniva is as effective as Fosamax and Actonel.

Merck has long been the market leader but loses patent protection in February 2008 on Fosamax, which had $3.2 billion in 2005 sales. The company has two potential osteoporosis drugs in human testing, said spokesman Chris Loder. He said Merck research shows Fosamax can reduce spine fractures by about 85 percent and hip fractures by about 50 percent.

On the Net:

Novartis: http://www.novartis.com

National Osteoporosis Foundation: http://www.nof.org