Though popular for its effectiveness and short courses, Zithromax can in some cases be associated with kidney disease.

Zithromax is manufacturer Pfizer Inc.’s brand name for azithromycin. It’s a macrolide antibiotic used to treat respiratory infections like bronchitis and sinusitis, skin infections like staph, and genitourinary infections due to sexually transmitted diseases.

Zithromax remains active in the body longer than other antibiotics before it breaks down. Instead of remaining in the blood, Zithromax gets transported by white blood cells and builds up in the tissues near the infection.

This longer “half-life” means that Zithromax can be administered in shorter courses than other antibiotics. Zithromax is sold in a five-day course pack under the brand name Z-Pak. Patients taking a Z-Pak start with a double dose on the first day, then they take a regular dose for each of the next four days. This schedule results in half the doses required for some other antibiotics.

There’s also a three-day course Z-Pak available for certain types of infection. For acute bacterial sinusitis and community-acquired pneumonia, Zithromax can be taken in a single large dose marketed under the name Zmax.

The availability of short and easy courses has kept Zithromax sales robust despite competition from generics. Sales of Zithromoax in 2012 reached $435 million.

But despite its popularity, Zithromax has been associated with serious kidney side effects in some cases. Reported Zithromax side effects have included interstitial nephritis and acute renal failure, according to the drug’s FDA-approved label.

Zithromax Kidney Failure

In one case reported in the Clinical Kidney Journal, a 16-year-old girl who had been otherwise healthy sought emergency treatment after ten days of vomiting, fatigue, and abdominal pain. Two weeks previously, she had taken a six-day course of azithromycin for bronchitis, but she had had no other medication.

Based on her renal failure, results of her urinalysis, and ultimately a renal biopsy, she was diagnosed with acute interstitial nephritis. She was given courses of two different steroid medications for over two weeks. Her normal kidney function did not return for over six weeks.

Interstitial nephritis is an inflammation of the tissue that surrounds the tubules within the kidney. It most commonly occurs as the side effect of a drug, like Zithromax.

Symptoms of interstitial nephritis are unpredictable and vary widely: they may include abnormal amounts of urine (either less or more than usual), pain with urination, fever, or pain in the lower back or side. There may also be a rash or itchiness, nausea, vomiting, reduced appetite, or difficulty breathing.

Renal failure, which often follows from interstitial nephritis, is simply the inability of the kidneys to do their job of filtering waste products from the blood. The kidneys also fail to control levels of water, electrolytes and acidity in the blood.

Kidney failure can lead to elevated blood pressure or anemia (a decrease in the number of red blood cells). It can also make bones weaker, and when it happens in children it can harm bone growth.

Whether or not kidney failure is treatable varies from case to case. The condition may resolve, or it may progress and be incurable. In cases of total Zithromax kidney failure, the only options may be dialysis or kidney transplant.