Zithromax Heart Rhythm Side Effects Questioned By New Study

New research raises questions about the potential link between Zithromax and heart problems, finding no increased risk when compared to some other antibiotics. 

The study was published last month in the Canadian Medical Association Journal (CMAJ), indicating that there may be confounding factors that have led some researchers to believe that the side effects of Zithromax (azithromycin), also known as Z-Pak, may increase the risk of heart problems.

Researchers looked at data on 14 million new antibiotic users in Europe and the U.K., through a nested case-control study using population-based health care databases. The findings indicate that 12,874 of those users developed ventricular arrhythmia, only 30 of whom used Zithromax.

“In the pooled data analyses across databases, azithromycin use was associated with an increased risk of ventricular arrhythmia relative to nonuse of antibiotics,” the researchers noted. “This increased risk disappeared when current amoxicillin use was the comparator.”

While the risk of ventricular arrhythmia nearly doubled when the researchers compared the use of the antibiotic to non-users, they determined that the fact that the risk disappeared when compared to another antibiotic suggests that confounding factors, which may not be related to Zithromax side effects, could be playing a role.

The FDA issued a Zithromax drug safety communication in March 2013, warning that the antibiotic can cause serious and potentially fatal abnormal heart activity. The FDA indicated that Zithromax can disrupt the electrical activity of the heart. The agency’s conclusions came after an investigation into the risk of Zithromax heart issues that was started in May 2012, examining data from a number of studies.

In May 2012, a study published in the New England Journal of Medicine first warned about the potential heart risks. Researchers found patients were 2.5 times more likely to die due to heart related problems on a five day Zithromax treatment when they compared it to treatment with other antibiotics or no antibiotic therapy.

Macrolides have been known to cause abnormal heart rhythm problems, including QT interval prolongation. These side effects can lead to a fatal heart condition, known as torsades de pointes.

Other studies have warned of more possible problems linked to the medications. In March 2015, a study published in PLOS One found that when pregnant women took macrolides, they were at an 80% increased risk of giving birth to a child born with cerebral palsy or epilepsy.

Another study, published in November 2015 by Chinese researchers, also linked Zithromax use to an increased risk of heart attacks.