LOS ANGELES - Medications called bisphosphonates are standard tools for the treatment of osteoporosis. They include Fosamax, Boniva, Actonel and Reclast. But new data released Wednesday raise some concern about whether the drugs are safe for long-term use.

Although the medications help increase bone quantity in the short term, two studies presented at the annual meeting of the American Academy of Orthopaedic Surgeons suggest that they may impair bone quality if used for four years or more.

The drugs may suppress the body's natural process of remodeling (removal and replacement of bone tissue) resulting in brittle bones that are prone to fracture.

In one study, 111 postmenopausal women who had been taking bisphosphonates for at least four years had an increased risk for an unusual type of femur fracture compared with 50 similar women who were taking calcium and vitamin D supplements for bone health.

The researchers stressed, however, that the drugs are still useful in the early years of use and people should not stop taking them. But more research is needed, said Dr. Melvin Rosenwasser of Columbia University Medical Center in a news release.

"Bisphosphonate use is still a very effective solution that prevents bone loss in most patients and no one is recommending that physicians avoid prescribing these," he said. "However, as baby boomers age and continue to remain active, it is important that we conduct more research and develop sustainable, safe and effective treatments for osteoporosis."