Azithromycin (Zithromax, Zmax) is used to treat a variety of bacterial infections 1. The antibiotic comes in different doses and forms, including tablets, eye drops and injectable solution. The 250 mg oral dose of azithromycin is often used to treat pneumonia, sinusitis, sexually transmitted diseases and skin infections 1. Although azithromycin is generally safe, like all medications, it can have side effects 1. The most common side effects involve the digestive system, but other areas of the body can also be affected.

Diarrhea

Diarrhea is the most common side effect with azithromycin, affecting approximately 4 to 5 percent of people, according to the U.S. Food and Drug Administration-approved prescribing information 1. However, diarrhea is more likely to occur with higher doses of azithromycin than with 250 mg doses 1. Rarely, diarrhea can be caused a Clostridium difficile infection of the intestine, a serious condition associated with antibiotic treatment 3. Signs and symptoms of this infection include fever, watery diarrhea and abdominal pain, warranting an immediate call to your doctor.

Other Digestive System Side Effects

Nausea, vomiting and abdominal pain are relatively common side effects of azithromycin, affecting approximately 3 percent of people who take the medication, according to the prescribing information 1. Like diarrhea, however, these side effects are more common with higher azithromycin doses than with 250 mg doses 1.

Nervous System Side Effects

Neurological symptoms such as dizziness, headache and fatigue can occur in a small portion of people who take azithromycin 1. Experimental evidence noted in the prescribing information indicates these side effects occur in less than 1 percent of people taking the medication. These symptoms typically aren't severe and rarely lead to discontinuing azithromycin 1.

Skin Side Effects

Skin-related side effects, such as rash and sun sensitivity, occur in less than 1 percent of people taking azithromycin 1. However, it's important to use sunscreen while taking this antibiotic. Another possible skin-related side effect is angioedema, which is swelling of the deep skin layers, often around the eyes and mouth. This side effect can be serious. If you experience throat tightness or trouble breathing, seek medical care immediately.

Rare But Serious Side Effects

Although rare, potentially life-threatening conditions can occur after taking azithromycin 1. Anaphylaxis is a severe, whole-body allergic reaction. Common symptoms include hives, itchiness, difficulty breathing and lightheadedness. A severe skin reaction can also develop, leading to blistering and loss of the top skin layer. This typically begins several days to weeks after taking azithromycin and starts with flu-like symptoms and a painful rash 1. A dangerous heart rhythm known as QT prolongation is another rare side effect, with symptoms including the sensation of an irregular heartbeat and fainting. Liver damage occurs rarely with azithromycin, usually accompanied by abdominal pain, itching and yellow discoloration of the skin 1.

Warnings and Precautions

If you develop symptoms of any of the serious side effects of azithromycin, stop taking the medication and call your doctor immediately 1. Seek emergency medical care if you experience symptoms of anaphylaxis.

Azithromycin is a pregnancy category B drug, which means animal studies have not shown a risk to the fetus, but there are no definitive studies in pregnant women 1. If you're pregnant, discuss the risks and benefits of taking azithromycin with your doctor 1. Also discuss potential effects if you're a nursing mother as small amounts of azithromycin can be excreted in breast milk 1.