Alendronate, a bisphosphonate agent that alters body calcium levels when used to treat osteoporosis, may be associated with increased risk for atrial fibrillation, according to an article in the April 28 issue of Archives of Internal Medicine.

Some recent studies have reported atrial fibrillation as an unexpected adverse effect of bisphosphonates, according to background information in the article.

Susan R. Heckbert, MD, PhD, of the University of Washington and Group Health, Seattle, and colleagues studied 719 women with confirmed atrial fibrillation that began between 2001 and 2004 and 966 age-matched controls who did not have atrial fibrillation.

More patients with atrial fibrillation than controls had ever used alendronate (47 or 6.5 percent versus 40 or 4.1 percent). After adjusting for other risk factors, use of alendronate was associated with a higher risk of atrial fibrillation compared with never having taken a bisphosphonate. The researchers estimated that approximately three percent of new atrial fibrillation cases in this population may be attributed to alendronate use.

Bisphosphonates may disrupt the function of regulatory proteins, trigger inflammation and cause small decreases in blood calcium and phosphate levels, the authors noted. "More information is needed about whether bisphosphonates could have effects on atrial tissue in the long term through these or other mechanisms that favor the initiation or persistence of atrial fibrillation," they wrote.

"In conclusion, all drugs have benefits and adverse effects. When new information becomes available about a previously unrecognized benefit or adverse effect, physicians and patients must reweigh the current knowledge about benefits and risks in making treatment decisions for each patient. The benefits of fracture prevention in patients at high risk for fracture will generally outweigh the possible risks of atrial fibrillation. However, it is important to carefully weigh the benefits against the possible risk of atrial fibrillation in women who have only modestly increased fracture risk and in women who have risk factors for atrial fibrillation, such as diabetes mellitus, coronary disease or heart failure."

"The decision to treat an individual patient with a given medication for a specific condition should be made with consideration of the risks associated with no treatment and of the benefits, risks and adverse effects of each therapy," wrote Jane A. Cauley, DrPH, and Kristine E. Ensrud, MD, MPH, of the University of Pittsburgh, in an accompanying editorial.

"Future research should evaluate the effectiveness of such strategies in presenting risks and benefits of therapies on patient understanding, compliance and risk of health outcomes."