Fosamax Femur Fracture Theory Questioned by Researchers

A case study published late last month in the New England Journal of Medicine (NEJM) is raising questions about one theory that tries to account for the higher femur fracture risk seen among users of <"">Fosamax and other bisphosphonates. The case study involves a 55-year-old woman who took 5 mg of Fosamax per day for nine years, and suffered Fosamax femur fractures. According to the report, a bone biopsy found no evidence of bone turnover suppression.

It’s long been surmised that bone turnover suppression was behind the femur fractures seen among post-menopausal women taking bisphosphonates like Fosamax. “The fact that bisphosphonates decrease bone resorption and formation and also have a long half-life in bone has led to the common belief that atypical fractures associated with bisphosphonate use are due to the marked suppression of bone turnover, resulting in the accumulation of microdamage that can lead to fractures,” the NEJM article states.

The subject of the NEJM case study suffered femur fractures in April 2009. At the time she “presented with a 3-month history of pain in both thighs, reporting that the pain had not been preceded by a fall or any injury. Radiographs of her femurs revealed incomplete stress fractures in both bones that involved the lateral cortex.”

According to the report, a bone biopsy performed at a site just below the point of fracture revealed “normal lamellar bone texture, no evidence of a dynamic bone at the endosteal or cortical envelope, no mineralization impairment, and no evidence of osteomalacia.”

“Our findings lead us to question the commonly held notion that atypical fractures associated with long-term use of bisphosphonates are the result of the oversuppression of bone turnover. More research in this area is needed,” the case study authors write. However, they also held out the possibility that signs of bone turnover oversuppression were obscured by new growth caused by the body’s attempt to heal the broken bone, a process known as accelerated remodeling.

Oral bisphosphonates like Fosamax, Reclast, Actonel and Boniva are taken by more than 5 million Americans every year, most of whom are post-menopausal women taking them to prevent or treat osteoporosis. However, few studies have been conducted to assess the drugs’ long-term risks. Last year, the U.S. Food & Drug Administration (FDA) added information to the “Warnings and Precautions” section of the drugs labels’ describing the risk of atypical thigh fractures. According to a recent Dow Jones report, there have been at least 300 reports of atypical thigh fractures in patients taking the drugs, often for longer than five years.

In September, a panel of FDA advisors agreed that Fosamax and other oral bisphosphonates need stronger warnings regarding duration of use because of their possible long-term risks. But the panel could not agree if use of the drugs should be limited to five years, or how new warnings should be worded.

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