Since 2013, the U.S. Food and Drug Administration has warned consumers that the increased likelihood of heart death in adults who take azithromycin, especially patients considered “high risk,” was significant enough for doctors to consider prescribing other antibiotics.

In 2012, The New York Times reported that the increased odds of death are small, but significant enough that the authors of the Zithromax study say doctors should consider prescribing a different drug, like amoxicillin, for high-risk patients who need antibiotics.

“People at high risk include those with heart failure, diabetes or a previous heart attack, and those who have undergone bypass surgery or have had stents implanted,” the Times reported. “In such patients, the drug may cause abnormal heart rhythms that can be fatal. Just how the drug might disrupt heart rhythm is not known, the researchers said.”

The following year the FDA issued a warning that azithromycin (Zithromax or Zmax) can cause abnormal changes in the electrical activity of the heart that may lead to a potentially fatal irregular heart rhythm.

The warning reads: “Patients at particular risk for developing this condition include those with known risk factors such as existing QT interval prolongation, low blood levels of potassium or magnesium, a slower than normal heart rate, or use of certain drugs used to treat abnormal heart rhythms, or arrhythmias.

“This communication is a result of our review of a study by medical researchers as well as another study by a manufacturer of the drug that assessed the potential for azithromycin to cause abnormal changes in the electrical activity of the heart.

“The azithromycin drug labels have been updated to strengthen the Warnings and Precautions section with information related to the risk of QT interval prolongation and torsades de pointes, a specific, rare heart rhythm abnormality. Information has also been added regarding the results of a clinical QT study which showed that azithromycin can prolong the QTc interval.”

The FDA’s warning came 10 months after the New England Journal of Medicine published the results of a study showing a small increase in cardiovascular deaths among patients treated with Zithromax compared to those given the antibiotics amoxicillin or ciprofloxacin or no treatment at all.

The commonly used antibiotic marketed by Pfizer Inc. is prescribed to treat things like bacterial respiratory infections, skin infections, ear infections, and sexually transmitted diseases. Patients who take the drug were found to more than double their risk of heart death.

Dr. John G. Bartlett, a professor of medicine at Johns Hopkins University School of Medicine and a former president of the Infectious Diseases Society of America, told the Times that the study’s results are cause for concern.

“He said he was convinced by the study because it included data on a huge number of patients and because the findings were biologically plausible, given that related drugs had also been found capable of disrupting heart rhythm,” the newspaper reported. “For patients at high risk, he would prescribe a different drug, he said, adding that there are plenty of alternatives.”