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Bisphosphonate Use Tied to Poor Bone Quality


 

Early results from two small studies show that the long-term use of oral bisphosphonates could harm bone quality and potentially lead to an increased risk for femur fractures, but the Food and Drug Administration is advising patients to stay on their medication unless advised by their physicians to stop.

The studies showed an association between the use of bisphosphonate treatments for 4 or more years and decreasing bone quality, possibly because the bisphosphonates altered the material properties of the bone. The two studies were presented at the annual meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

“Although bisphosphonates have demonstrated an improvement in bone quantity, little if anything is known about the effects of these drugs on bone quality,” Brian Gladnick, one of the investigators from the Hospital for Special Surgery in New York, said in a statement.

Researchers at the Hospital for Special Surgery conducted a prospective pilot study in which they evaluated the bone composition of 21 postmenopausal women who presented to the emergency department with proximal femoral fractures. Of the patients enrolled in the study, 12 had a history of bisphosphonate use for an average of 8.5 years. Nine of the women had never been treated with bisphosphonates.

The researchers performed bone core biopsies for each patient and analyzed both the micro-architecture and material properties of the bone. No difference in the bone micro-architecture was observed, but among the patients who had been treated with bisphosphonates, the investigators found reduced bone tissue heterogeneity. Specifically, those who had received bisphosphonates had reduced mineral content and crystal size, compared with the control group. This study was supported by a grant from the National Institutes of Health.

In a second study, researchers at Columbia University in New York evaluated the bone structure of 111 postmenopausal women with primary osteoporosis. Of that group, 61 had been taking bisphosphonates for at least 4 years. The other 50 women had been taking calcium and vitamin D supplements.

The researchers at Columbia saw improved structural integrity early in the bisphosphonate treatment. However, the trends began to reverse after 4 years of treatment. After that point, continued treatment was associated with decreased axial strength and structural integrity. The researchers received no compensation for this study.

Both groups of investigators called for more research to gauge the effectiveness of long-term clinical use of bisphosphonates for osteoporosis treatment. However, they did not expect the findings to affect clinical practice anytime soon.

“The message here is bisphosphonates are not bad drugs, but perhaps we need to know more about the long-term effects,” Dr. Melvin Rosenwasser, professor of orthopaedic surgery at Columbia University and one of the investigators on the Columbia study.

Further research could shed light on the best treatment approaches in women who have been taking bisphosphonates for more than 4 years. For example, it would be helpful for physicians to know the effects of a bisphosphonate drug holiday on bone quality, Dr. Rosenwasser said in an interview.

The FDA advised physicians to be aware of the possible risk of atypical subtrochanteric femur fractures in patients taking bisphosphonates, but said that at this point they saw no “clear connection” between bisphosphonate use and the risk of these fractures. “FDA is working closely with outside experts, including members of the recently convened American Society of Bone and Mineral Research Subtrochanteric Femoral Fracture Task Force, to gather additional information that may provide more insight into this issue,” the agency said in a statement.

The agency has been following the issue since 2008, when case reports were published showing that atypical subtrochanteric femur fractures were occurring in women with osteoporosis who were using bisphosphonates. In June 2008, the FDA requested information from all bisphosphonate drug manufacturers about this potential safety issue. However, the agency's review of the information did not show an increased risk for women using bisphosphonates.

Some of the manufacturers of bisphosphonate therapies (Fosamax, Actonel, Boniva, and Reclast) issued statements pledging to continue to monitor reports of atypical fractures, but stand by the benefits of the therapies.

The best information available to date indicates that atypical subtrochanteric fractures are rare, said Dr. Elizabeth Shane, an endocrinologist at Columbia University who also co-chairs the American Society for Bone and Mineral Research Subtrochanteric Femoral Fracture Task Force.

Preliminary estimates are that less than 1 in 10,000 patients taking bisphosphonates suffers from this type of fracture, she said. Contrast that with the fact that treating 1,000 women for 3 years with bisphosphonates can prevent 100 fractures, and the benefit of taking these drugs far outweighs the risks, said Dr. Shane, who receives research support from Eli Lilly, Merck, and Novartis.

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