FDA Issues Stronger Warning On Pfizer's Antibacterial Antibiotic Zithromax

The U.S. Food and Drug Administration (FDA) has Tuesday sent out a strong warning to the public related to drug giant Pfizer, Inc.'s (PFE) popular antibiotic Zithromax or Zmax (azithromycin), warning that the drug can cause fatal irregular heart rhythm in some patients. Azithromycin belongs to a class of antibacterial drugs called macrolides.

In its drug safety announcement on its website, the FDA said the drug "can cause abnormal changes in the electrical activity of the heart that may lead to a potentially fatal irregular heart rhythm."

The FDA added the patients with conditions 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, are more prone to be affected and are at particular risk.

The FDA strengthened its warning following the review of a May 17 study results, by medical researchers as well as the company to assess Zithromax's potential for causing abnormal changes in the electrical activity of the heart.

The FDA noted that azithromycin drug labels have already been updated to strengthen the 'warnings and precautions' section.

The FDA also warned that health care professionals should consider the risk of fatal heart rhythms with azithromycin when considering treatment options for patients who are already at risk for cardiovascular events.

Previously, the FDA had in May 2012 released a statement about a New England Journal of Medicine study that compared the risks of cardiovascular death in patients treated with the antibacterial drugs azithromycin, amoxicillin, ciprofloxacin (Cipro), and levofloxacin (Levaquin), or no antibacterial drug.

The study reported an increase in cardiovascular deaths, and risk of death from any cause, in persons treated with a 5-day course of azithromycin (Zithromax) or levofloxacin compared to persons treated with other antibiotics such as amoxicillin, ciprofloxacin, or no drug.

PFE closed Tuesday's regular trading session at $27.94, down $0.31 or 1.10% on a volume of 29.71 million shares.

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