UNITED STATES (FOX44) — The Food and Drug Administration has issued a new warning about one of the most popular antibiotics in the United States.

FDA experts say Azithromycin, more commonly known as the Z-Pak, can cause a potentially fatal irregular heart beat in certain patients.

Studies show the drug can alter the electrical activity of the heart, which may lead to a condition in which the timing of the heart's contractions becomes irregular. These conditions can result in death.

The Z-Pak is commonly used to treat sinus infections and bronchitis.