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The Food and Drug Administration said Wednesday it's conducting a safety review of certain bone-building drugs like Fosamax and Boniva to see if they increase the risk of femur fractures.

The review involves a class of drugs known as bisphosphonates, which are commonly prescribed to treat osteoporosis and are designed to build bone mass. Drugs in the class include Actonel, marketed by Sanofi Aventis SA (SNY) and Procter & Gamble Co. (PG), Boniva, marketed by Roche Holding AG (RHHBY) and GlaxoSmithKline PLC (GSK), and Merck & Co.'s (MRK) Fosamax.

The agency said it was looking at reports about whether there's an increased risk of atypical subtrochanteric femur fractures--fractures in the bone just below the hip joint--in some patients who have been on the drugs for several years.

However, the FDA said, "the data that FDA has reviewed have not shown a clear connection between bisphosphonate use and a risk of atypical subtrochanteric femur fractures.

Two studies presented Wednesday at the American Academy of Orthopaedic Surgeons' annual meeting suggested the drugs might adversely affect bone quality and increase risk of atypical fractures of the femur, or the main bone in the thigh when used for four or more years.

The FDA said it had requested information from drug manufacturers in 2008 after seeing case reports about femur fractures occurring in women with osteoporosis using bisphosphonates.

"FDA's review of these data did not show an increase in this risk in women using these medications," the agency said in a statement posted to its Web site Wednesday. The agency also cited a 2008 study that found similar femur fracture rates among women taking bisphosphonates compared to women not taking the drugs. The study found that the femur fractures had many features in common with osteoporotic hip fractures.

However, the agency said it would work closely with outside experts, including members of the recently convened American Society of Bone and Mineral Research's Subtrochanteric Femoral Fracture Task Force, to gather additional information.

Merck, which makes Fosamax, said it has not seen any increased fracture risk with the drug at any skeletal site in clinical studies. Fosamax, which is also available as a generic drug, was approved in 1995 and was the first bisphosphonate approved in the U.S. The company said it has several ongoing studies to investigate fracture risks. The FDA said people currently taking the medications should not stop taking them but said they should talk to their doctors if they develop new hip or thigh pain. The agency asked doctors to report any side effects seen with bisphosphonates to the agency.

Bisphosphonates are designed to work by slowing or stopping bone loss by partially blocking the body's natural process that's involved in removing and rebuilding bone tissue. The drugs have been shown to increase bone mass and stop or slow the progression of osteoporosis.

But researchers said Wednesday that while the drugs are effective at increasing the quantity of bone, it's possible they might cause brittle bones over the long-term that are more susceptible to fractures.

One study by researchers at Columbia University looked at the bone structure of 111 postmenopausal women with osteoporosis, 61 of whom had been taking bisphosphonates for a minimum of four years and compared it to 50 people taking calcium and vitamin D supplements.

"In the early treatment period, patients using bisphosphonates experienced improvements in all parameters, including decreased buckling ratio and increased cross-sectional area," Melvin Rosenwasser, an orthopaedic surgeon for Columbia University Medical Center, said in a statement. "However, after four years of use, these trends reversed revealing an association between prolonged therapy and declining cortical bone structural integrity."

Rosenwasser said the drugs are still very effective at preventing bone loss and the findings from the study shouldn't change treatment practices. He said additional studies are needed.

Another, separate study, by researchers at the Hospital for Special Surgery in New York, looked at bone samples taken from 21 post-menopausal women who were treated for femoral fractures. Of these, 12 patients had a history of bisphosphonate treatment for an average of 8.5 years, while nine women hadn't been treated with the drugs.

The study found that patients who had been treated with bisphosphonates had a reduction in bone tissue heterogeneity compared with women who had not received the drugs, which researchers said suggests there might be differences in some bone-quality parameters.

-By Jennifer Corbett Dooren, Dow Jones Newswires; 202-862-9294; jennifer.corbett@dowjones.com

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