Prolonged use of the bisphosphonate alendronate may increase the risk of low-energy fractures of the femoral shaft, according to physicians at the Weill Medical College of Cornell University.
"Increasing evidence suggests long-term alendronate use may overly suppress bone metabolism, limiting repair of microdamage and creating risk for insufficiency fractures," Dr. Joseph M. Lane and colleagues write in the May/June issue of the Journal of Orthopaedic Trauma.
To investigate this risk, the New York-based research team reviewed the cases of all 70 patients with low-energy subtrochanteric and midshaft femur fractures admitted to their Level 1 trauma center between 2002 and 2007.
The mean age of the patients was 74.7 years, and 59 were women. Records showed that 25 patients (36 per cent) were being treated with alendronate.
Review of the patients' radiographs identified 20 patients with "a simple, transverse, or short oblique (fracture) pattern in areas of thickened cortices with a unicortical beak."
Nineteen of the 20 patients with this fracture pattern were taking alendronate (odds ratio 139, p < 0.0001), the authors report. The other patient was later diagnosed with multiple myeloma.
Mean duration of alendronate use was significantly longer in patients with femoral stress fractures than in the six treated patients without this type of fracture (6.9 vs 2.5 years, p = 0.002).
Otherwise, there were no significant differences in age, race, body mass index, or history of osteoporosis among patients with and those without this fracture pattern, the report indicates.
Dr. Lane and his associates speculate that "adynamic metabolism from impaired resorption may be the underlying pathophysiology that leads to these fractures."
They call for further research to determine if this effect is associated with all bisphosphonate drugs, and if it became apparent first with alendronate because it has been available for the longest time and is the most widely used.
In the meantime, "physicians prescribing bisphosphonates for longer durations should monitor patients for indications of bone regeneration," Dr. Lane advises in a university press release. "In situations where a blood test reveals low bone turnover, a holiday from the bisphosphonates would be recommended until these markers return to an acceptable level."
