The Food and Drug Administration (FDA) has begun a year-long evaluation to determine whether the bisphosphonate drugs, used to increase bone density in postmenopausal women, heighten the risk of atrial fibrillation. The agency is taking the action in response to an article and a letter to the editor in the May 3, 2007, issue of the New England Journal of Medicine indicating that women who had received either the weekly oral bisphosphonate alendronate (Fosamax) or the once-yearly iv infusion bisphosphonate zoledronic acid (Reclast) were more likely to develop serious atrial fibrillation (that which is life threatening, necessitates hospitalization, or results in disability) than those who received a placebo.

The overall incidence of atrial fibrillation (cases that were serious and those that were not) was comparable among the two groups, suggesting that if a patient develops it, it's more likely to be a serious occurrence if she or he has had bisphosphonate therapy. The FDA's analysis of postmarketing reports of atrial fibrillation linked to oral and IV bisphosphonates has not identified any particular factors that might heighten risk. Clinical trials performed before the approval of once-yearly zoledronic acid did not show a greater incidence of atrial fibrillation, as measured by electrocardiography, as long as 11 days after infusion of the drug. Most of the patients who developed atrial fibrillation did so more than a month after infusion. The FDA is seeking more information and will continue to look for problems related to the use of all bisphosphonates. At present, no warning is being added to drug labeling, and patients aren't being asked to discontinue therapy. However, it's prudent for nurses to look for signs of atrial fibrillation in patients receiving bisphosphonates while the FDA continues its evaluation.