Research has revealed some disturbing link between Reclast, made by Novartis AG and Fosamax manufactured by Merck and Co and irregular heart rhythm, though only in a small number of women users. Both are known bone-building drugs.
The signs of a problem seem to be more pronounced with Reclast, given as an annual shot. But there was a hint of similar trouble in a few women who took the leading osteoporosis pill, Fosamax by Merck & Co. They are all at risk for a condition called atrial fibrillation, an irregular heart rhythm that can cause strokes.
Though it is still uncertain how big a worry it might be, experts agreed the overall risk is small. They said women at high risk for bone breaks _ the main target of these osteoporosis drugs _ should keep taking them as prescribed.
Two separate reports published Thursday in The New England Journal of Medicine point to elevated rates of serious episodes of that heart condition in women.
"For the first time, there may be a side effect," said a researcher involved in both studies, Dr. Steven Cummings of California Pacific Medical Center Research Institute. Until now, people have assumed Fosamax "was completely safe and could be given to almost anybody."
Fosamax, the Merck brand name for alendronate, is now used by an estimated 1.8 million American women. In a letter to the medical journal, Cummings reported evidence of the heart problem found in a recent review of a 1997 Merck-sponsored study of postmenopausal women on Fosamax.
There appeared to be 50 percent more risk of the serious heart rhythm in women who took the daily pill than among those who didn't take it. About half of the 6,459 women took Fosamax, and 47 developed atrial fibrillation, compared to just 31 cases among the other women.
However, the finding, while not statistically definitive for Fosamax, worried some researchers because it is in line with the results of a new study published in the same issue of the medical journal.
This study of 7,736 postmenopausal women with bone-thinning osteoporosis focuses on Reclast. Novartis recently won approval to sell Reclast, known generically as zoledronic acid, for Paget's disease, another bone condition. The company hopes to get an OK later this year to sell it for osteoporosis use.
The new study, funded by Novartis, shows that Reclast works at least as well as existing drugs in the same class, researchers say. However, the risk of a serious case of irregular heart rhythm was more than double that in the other patients _ 50 cases in the drug-taking half, compared to 20 cases in the others.
Researchers cautioned about overestimating the importance of the heart rhythm problem. The Reclast study showed little apparent difference in overall cardiac deaths and the overall risk of the rhythm condition remained small.
Doctors made available by Merck and Novartis said the side effect could be a statistical fluke or just a product of aging. They said earlier studies showed no sign of the possible side effect.
For now, it's unknown if the possible risk applies to other drugs in the class known as biphosphonates. Future studies are expected to help clarify the risk.