FDA Strengthens Warnings On Pfizer Antibiotic Zithromax

By Jennifer Corbett Dooren

WASHINGTON - The U.S. Food and Drug Administration strengthened warnings on Pfizer Inc.'s ( PFE ) antibiotic Zithromax, saying there is a small chance the product may trigger a potentially fatal, irregular heart rhythm.

Zithromax is a commonly used antibiotic that is also available as a generic drug, azithromycin.

The FDA posted a notice to its website Tuesday, stating that the drug label for azithromycin has been updated to warn that the product cause changes in the heart's electrical activity, which in turn can cause abnormal heart rhythms.

The agency said patients who are at higher risk of developing heart-related electrical problems include those with existing heart trouble, those with low blood levels of potassium or magnesium and people with a slower-than-normal heart rate.

Pfizer didn't immediately comment on FDA's action.

Other drugs that fall into the same class of azithromycin carry a similar heart-related risk, FDA said, in addition to another category of antibiotics called fluoroquinolones.

More than 40 million people received a prescription for azithromycin in 2011, according to FDA. The antibiotic is approved to treat a variety of infections including sinusitis and pneumonia.

--Write to Jennifer Corbett Dooren at jennifer.corbett@dowjones.com

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