A drug that could become one of the first new treatments for osteoporosis in more than a decade built bone in women with the disease, a study released Friday said.

The drug alendronate was given to 516 women over three years, producing an average 6.8 percent increase in bone density at the spine, said Merck & Co., which plans next month to submit it for Food and Drug Administration approval. It usually takes about 19 months for a company to win marketing approval.Patients in the trials in 15 countries outside the United States also showed 4.8 percent and 6.9 percent increases at the two spots on the hip most prone to fracture.

"That's pretty substantial," said Richard Gelula of the National Osteoporosis Foundation in Washington. "If they can reduce bone loss, that's a fantastic achievement. If they can add some bone density" better yet.

If the drug works, it's good news for the 25 million Americans, many of them women, suffering from the brittle bone disease. It's even better news that other potential therapies are in the pipeline as well.

"In the next three to five years we should be seeing several new drugs," Dr. Ethel Siris, a Columbia University professor and an adviser to the FDA on proposed osteoporosis treatments.

"At the moment, we have perhaps one really effective therapy, hormone replacement therapy," said Dr. Ian Reid of the University of Auckland, clinical investigator in the alendronate trial, who presented his results at a conference in Melbourne, Australia.

"Patients . . . have an enormous need for an alternative," he said.

While the hormones estrogen and calcitonin have been the only approved forms of treatment since 1984, drugs that may actually stimulate bone growth are in the laboratory along with alendronate.

A University of California at San Francisco study released this week showed promising results with a parathyroid hormone.

A four-week trial of the drug on rats with lab-induced osteoporosis showed all the rats regained lost bone mass, and some actually added extra bone.

"This is really the first real chance we have to actually reverse osteoporosis," said Dr. Nancy Lane, the parathyroid study's lead author.

The university and at least one drug company have started human trials on parathyroid.

An early candidate for bone building, sodium fluoride, produced bones that weighed more but also snapped more. Developers of slow-release sodium fluoride, which preliminary studies found stimulates bone growth without making them more brittle, filed early findings with the FDA last month.

Alternatives are crucial because of the side effects of estrogen therapy.

"Estrogen is still overall the best thing you can offer women, but alendronate and the other drugs are not going to raise the specter of increased breast cancer risk, which is something we still have not resolved (with estrogen)," Siris said.

Still, estrogen can prevent bone loss and add bone mass, and it can prevent heart disease, Siris said.

The other approved treatment, calcitonin, must either be taken by daily injection or by nasal spray, which has not been shown to be as effective as shots.

"People say, `Please, we're suffering from a terrible bone disease, and we have very limited options,' " Siris said. "We very much need new, more acceptable, simply administered drugs. We need new drugs."