Liu said: "They [the study authors] say that osteoclasts did not die at an increased rate like they did in some of the animal studies but, rather, [Fosamax] slowed down the rate of death but also reduced the functionality or efficiency at which osteoclasts worked."
The FDA letter to the editor said the agency has received reports of 23 patients taking Fosamax who have been diagnosed with cancer of the esophagus (eight died) since the drug was first approved in 1995. Thirty-one patients from Japan and Europe also were diagnosed with this cancer after taking Fosamax.
"The concern is that there is an association, not cause-and-effect," said Liu. "The FDA doesn't really have enough evidence to say it [Fosamax] does anything to stimulate cancers [but] one of the side effects of oral bisphosphonates is that they can make GERD (gastroesophageal reflux disease) worse."
The prescribing information for Fosamax, made by Merck & Co., said that people with "certain disorders of the esophagus" should not use the drug.
In a news release, Merck said that "clinical trials of Fosamax and post-marketing reports do not suggest any association between alendronate and esophageal cancer. Fosamax has been studied in controlled clinical trials involving more than 17,000 patients, contributing as much as 10 years' data with alendronate."
Addressing the bone cell research by Weinstein, the release said the study findings support Merck research that "alendronate decreases the rate of bone resorption by osteoclasts without causing rapid osteoclast death and does not change the current clinical recommendations for the use of Fosamax."
Use of bisphosphonates has been associated with other problems in the past, including an increased risk of atrial fibrillation (a type of abnormal heart rhythm), unusual fractures of the thigh bone and inflammatory eye disease.
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