Azithromycin is one of America’s most prescribed drugs. It’s an antibiotic. Fifty two million prescriptions are written for it every year. Now a study in the New England Journal of Medicine links Azithromycin (also known as Z pack) to sudden cardiac death. Should you be concerned?

“The study is by a reputable author,” says Steven Nissen, MD, chair of Cardiovascular Medicine at Cleveland Clinic. “But this is an observational study, so we need to be cautious.”

The study reviewed a Medicaid database and found an increased risk for cardiovascular death, sudden death, and overall all-cause mortality associated with a 5-day course of azithromycin. The comparison was between patients who were taking azithromycin and those who were taking no antibiotics.

“This is similar to what we know about erythromycin [another antibiotic] which can increase the risk of heart rhythm disorders,” says Dr. Nissen. “Azithromycin may also increase the potential for people to have heart rhythm disturbances.”

Although the study was not a controlled, double-blind study (the gold standard in science), Dr. Nissen sees reason for caution. “People with heart disease should probably not take azithromycin. I would prescribe something else in this group at this time. If you have heart disease and you have an alternative – should take the alternative until further research gives us a definitive answer.”