SEATTLE - Another research study has found a possible connection between the bone-building drug Fosamax and irregular heart rhythms.

The study of the health records of 1,700 elderly women who were patients at Seattle's Group Health Cooperative found that the women who were taking the Merck & Co. drug had significantly increased odds of developing atrial fibrillation.

The condition can result in rapid and irregular heartbeat that can create clots and lead to strokes or cause shortness of breath and fatigue.

Two studies last year also found a possible connection between Fosamax and another bone-building drug, Reclast, made by Novartis AG, and irregular heartbeat problems.

"This is going to be an important study for physicians to be aware of," said Dr. Philip Mease, an osteoporosis expert at Swedish Medical Center in Seattle and a clinical professor of rheumatology at the University of Washington. Mease was not involved with the study.

Mease stressed, however, that the study of Fosamax, which is generically known as alendronate, turned up only an association not proof that it causes atrial fibrillation. The generic version of the drug became available in February. Mease warned patients taking Fosamax not to quit on their own.

"I'm concerned about the news leading to mass cessation" of the drug, Mease said, because it could lead to an increase in deaths from bone fractures.

The researchers at Group Health compared the health records of 719 women who had been diagnosed with atrial fibrillation at Group Health between 2001 and 2004 against those of 966 women who had never had the condition.

Among the atrial-fibrillation patients, 6.5 percent had taken Fosamax, compared with 4.1 percent in the other group. Researchers calculated that women who had taken Fosamax were 86 percent more likely to have atrial fibrillation than if they had never taken it.

Fosamax users who were diabetic or taking statins to lower cholesterol were among the most likely to develop irregular heartbeat.

"This adds to the evidence that there may in fact be an association" between the two, said Dr. Susan Heckbert, the study's first author and a professor of epidemiology at the University of Washington.

The paper examined only Fosamax, the world's top-selling osteoporosis drug and the preferred brand for Group Health members. It did not compare other bone-strengthening drugs in the same class.

The paper appeared Monday in the Archives of Internal Medicine. The National Heart, Lung and Blood Institute paid for the study.