Pfizer took a hit on Tuesday, when the Food and Drug Administration strengthened its Warnings and Precautions label to add a heart warning on the popular antibiotic drug azithromycin, also known as Zithromax, Zmax, or the “Z-Pak”. The FDA warns that prescribing doctors should be wary of patients with heart conditions since there is an increased risk of fatal heart arrhythmia in those prescribed Zithromax. Studies by Pfizer and the FDA showed a slightly increased cardiovascular death rate, especially in instances where the prescribed patient had previous heart problems, was taking additional medicine for a heart arrhythmia, or had a potassium or magnesium deficiency.

“Health care professionals should consider the risk of fatal heart rhythms with azithromycin when considering treatment options for patients who are already at risk,” the FDA said Tuesday in an official statement on the label update.

Lauren Starr, a spokeswoman for Pfizer, released a statement to ease concern and to report that the FDA warning had been updated on the Zithromax label. “The majority of patients treated with Zithromax (azithromycin) are not affected by this label update. [The drug] has had a well-established benefit risk profile for more than 20 years and continues to be an effective treatment option for patients all over the globe suffering from many types of bacterial infections,” she said.

Daniel Nigh, an attorney with Levin, Papantonio, commented, “It’s unfortunate when pharmaceutical companies, like Pfizer, put profits ahead of safety. When they do, the consumer is the one that’s left to pay the penalty.”

Zithromax (azithromycin) is a very popular antibiotic, also available in generic form, that is prescribed to treat a wide range of bacterial infections, from ear infections to more serious infections, such as pneumonia. In 2011, approximately 40 million patients were prescribed the “Z-Pak” in the United States.

Pfizer, the world’s largest drug manufacturer, also produces popular brands such as the anti-anxiety pill Xanax (alprazolam), the over-the-counter pain reliever Advil (ibuprofen), and the anti-depressant Zoloft (sertraline).

Krysta Loera is a writer and researcher with Ring of Fire.