Pfizer Inc. (PFE)’s antibiotic Zithromax and its generic competitors carry a “small increase” in the risk of cardiovascular death compared with another common antibiotic, a study found.

The pills, which are used to treat infections, caused a “small absolute increase in cardiovascular deaths” among patients, particularly those who had a higher chance of heart problems, according to the study published today in the New England Journal of Medicine.

The U.S. Food and Drug Administration “is reviewing the results from this study and will communicate any new information that results,” the agency said in a statement posted on its website.

The study looked at 350,000 patient prescriptions for azithromycin taken by people in Tennessee covered by Medicaid, the state-U.S. health program for the poor. The research showed that 85 of every 1 million treatment courses of the drug were associated with cardiac death. That’s more than twice the rate on the antibiotic amoxicillin, according to the study.

“We are thoroughly reviewing this observational study within the overall context of the data we’ve collected for more than two decades on Zithromax’s benefits and risks,” Joan Campion, a Pfizer spokeswoman, said in an e-mail.

Zithromax generated about $453 million for Pfizer last year. The drug no longer has patent protection and generic versions also are sold. The medicine is prescribed in patients to treat bacterial infections of the respiratory system and urinary tract and for tonsillitis.

(Source: Bloomberg)