A pair of research reports suggest a possible link between two bone-building drugs and irregular heart rhythms in a small number of women who take the meds. The signs of a problem were more pronounced with Reclast, a Novartis drug that’s given as an annual shot. But there was a hint of similar trouble in a few women who took Merck’s Fosamax osteoporosis.

The safety question caught researchers by surprise. While uncertain how big a worry it might be, they agreed the overall risk is small. Specialists said women at high risk for bone breaks — the main target of these osteoporosis drugs — should keep taking them as prescribed.

But several experts said they’d be cautious about those who also are at risk for a condition called atrial fibrillation, an irregular heart rhythm that can cause strokes. The two separate reports published today in The New England Journal of Medicine point to elevated rates of serious episodes of that heart condition in women who took Reclast and Fosamax.

“For the first time, there may be a side effect,” says Steven Cummings of California Pacific Medical Center Research Institute, who was involved in both studies. Until now, people have assumed Fosamax “was completely safe and could be given to almost anybody.”

Fosamax is used by an estimated 1.8 million American women. In a letter to the 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 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. However, the risk of a serious case of irregular heart rhythm was more than double that in the other patients - 50 cases given the drug, compared to 20 cases in the others.

Doctors made available by Merck and Novartis say the side effect could be a statistical fluke or just a product of aging, and that 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.

Source: Associated Press
Study in the NEJM (subscription required);
Letter in the NEJM (subscription required).[tags]Fosamax, Merck, Novartis, Reclast[/tags]