Cancer patients treated with osteoporosis-fighting drugs are at increased risk of abnormal heart rhythms and stroke, new research shows.

The benefits of these drugs for preventing and treating cancer after it has spread to the bone-especially in breast cancer patients-still outweigh their risks, said the study’s lead author, as long as patients are monitored closely.

“These drugs are still very, very, very valuable drugs,” said Dr. James S. Goodwin of the University of Texas Medical Branch in Galveston. “The risk of stroke from atrial fibrillation can be entirely prevented if we’re on top of it.”

Atrial fibrillation, an irregular beating rhythm in the heart’s upper “atrial” chambers, increases stroke risk because blood pools in the poorly functioning chambers, leading to clotting; clots can then break off and travel to the brain, causing a stroke.

Intravenous bisphosphonates, which include Aredia and Zometa, are used in healthy people to treat osteoporosis. Studies had already linked these drugs to atrial fibrillation and stroke, but in 2008 the U.S. Food and Drug Administration concluded after a review of safety data that “healthcare professionals should not alter their prescribing patterns for bisphosphonates and patients should not stop taking their bisphosphonate medication.”

Doses of bisphosphonates given to treat cancer patients with bone metastasis are typically 10 times higher than doses used in patients with osteoporosis.

Because these patients may also be on other potentially heart-damaging chemotherapy medications, Goodwin and his colleagues investigated heart risks by reviewing data on nearly 7,000 Medicare patients with cancer who took bisphosphonates and nearly 14,000 cancer patients on Medicare who had not been prescribed the drugs. They report their findings in the Journal of Clinical Oncology.

The cancer patients taking bisphosphonates were at a 30 percent increased risk of atrial fibrillation compared to those who were not given the drugs, the researchers found. While people not on the medications had a 25 percent risk of having atrial fibrillation during the six-year follow up period, the risk for people on bisphosphonates was 33 percent; for stroke, the risks were 15 percent and 19 percent, respectively.

If doctors find that a patient has atrial fibrillation-which they can do by simply listening to the heart-they can immediately prescribe blood-thinning drugs to prevent a stroke, the researcher said.

In an editorial accompanying the study, Dr. Julie R. Gralow of the University of Washington School of Medicine in Seattle concludes that “the jury is still out” on whether bisphosphonates increase the risk of abnormal heart rhythms and stroke. Nevertheless, she adds, “Before prescribing any bisphosphonates, risks and benefits must be carefully weighed by physicians and well-informed patients.”

SOURCE:  Journal of Clinical Oncology, published online October 12, 2010.