Bone Loss Drug Linked to Rare Fracture

March 19, 2008 -- Long-term use of the osteoporosis drug Fosamax may weaken the bones in a small subset of people taking the drug.

Patients who suffer this unusual side effect suffer broken legs after minor falls. It's likely that other drugs in the same class as Fosamax -- the bisphosphonates -- have the same rare side effect. It is seen in only a small number of patients who took the drug for more than five years.

Joseph M. Lane, MD, chief of the metabolic bone disease service at New York/Presbyterian Hospital and professor of special surgery at Weill Medical College of Cornell University and colleagues report the side effect in a letter to the March 20 issue of The New England Journal of Medicine.

"There is a subset of patients for whom the longer they take bisphosphonates, the more they turn off the internal repair of the bone. This sets them up for bone fractures after trivial falls," Lane tells WebMD. "Is everyone who takes a bisphosphonate going to get this? No. This is a subset of patients. But we cannot say what makes these patients unique. And is it unique to this one bisphosphonate, or to all drugs in this class? We don't know."

Lane and colleagues report 15 cases of unusual bone fractures in postmenopausal women who had been taking Fosamax for more than five years. All had fractures along the length of the femur, the long bone in the thigh, after falls from standing position or lower.

Ten of the patients had a distinct and unusual fracture pattern. These patients had been taking Fosamax for more than seven years on average; the other five patients averaged less than three years of Fosamax use.

"People on prolonged bisphosphonates -- and Fosamax is the only one we have seen so far -- after five to seven years they are at risk of fractures in the long bone of the leg," Lane says. "They complained of thigh pain for months before the breaks. So it seems they start off with a stress fracture that is unrecognized, and it goes on to full fracture."

Susan Bukata, MD, director of the center for bone health at the University of Rochester, New York, says orthopaedic surgeons and specialists in metabolic bone disease are well aware of this problem. Bukata was not involved in the Lane report.

"This is not seen only with Fosamax. We see this in cancer patients given high doses of Zometa as well," Bukata tells WebMD. "Fosamax was the most commonly used bisphosphonate for the longest time. And it takes several years on the drug before it seems to be a problem. So more people have been on Fosamax long term than on Actonel or the several other bisphosphonates."