Letters Question Findings of Study on Zithromax Heart Problems

Some health care professionals are questioning the science behind a recent study that suggested side effects of Zithromax may increase the risk of cardiovascular death, while others indicate that the findings highlight a need for more antibiotic restraint in the medical community.

Following a May 2012 study published in the New England Journal of Medicine, a number of letters to the editor were published by the journal this month, from doctors, scientists and even a Pfizer employee who wrote to defend the drug.

Azithromycin, which is most commonly known by the brand name Zithromax or “Z Pak”, is a widely used antibiotic that is part of a class of medications known as macrolides. Other medications that are part of the same class have previously been associated with an increase in the risk of sudden death due to heart problems. 

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The original study found that were 47 more deaths for every million people who took Zithromax than for those who took Amoxicillin. That number increased to 245 more deaths per million when the focus was specifically on patients already at risk for heart problems.

Researchers looked at Tennessee Medicaid record that included more than 347,000 patients who took Zithromax or a generic equivalent, nearly 1.4 million who took no antibiotics, 1.3 million who took amoxicillin, 264,000 who took Cipro and 264,000 who took Levaquin.

The same day the study was released, the FDA issued a statement indicating that they were reviewing the data and evaluating the potential Zithromax heart problems. The medication already carries a heart rhythm warning, after the FDA investigated all macrolides due to the problem in 2011.

In last weeks issues of the New England Journal of Medicine five different Letters to the Editor were published in response to the study.

“Given the inherent weaknesses of observational studies, the excess deaths reported by Ray and colleagues may or may not have been due to azithromycin,” wrote Doctors Richard K. Albert,  John Connett and Prescott G. Woodruff in one of the letters. “Our randomized trial, however, indicated that long-term use of azithromycin had benefits that outweighed potential cardiovascular risks when patients at greatest risk were excluded and the QTc interval was monitored.”

Another letter written by Pfizer scientists noted that other studies failed to find an increase in the risk of heart problems and called on others to look at all of the studies on Zithromax safety.

Two Brazilian doctors noted that many of the Zithromax prescriptions recorded by the study were likely unnecessary, and pointed out that lives could have been saved if doctors used more restraint in prescribing it and other antibiotics.

The original researchers published a response to the letters, defending the science of their study in detail, and agreeing with those who called for more antibiotic use restraint.


  • JEANNEMarch 14, 2013 at 2:58 pm

    I have a heart condition already, so if my doctor knew that should she have put me on the zpack. I am also taking a high blood pressure beta blocker toprol xl along with diabeties medicine glipizide.

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