Though they’re not among the more common side effects of Zithromax, kidney disorders have been linked to the popular antibiotic and have allegedly led to serious and permanent complications for some patients.

Manufactured by Pfizer, Zithromax and Zmax are the brand names for azithromycin. Zithromax belongs to a class of antibiotics called macrolides, which fight bacteria by operating on bacterial DNA to prevent growth and reproduction. Zithromax is now indicated as a treatment for bacterial infections of the skin, respiratory system, genitourinary system, and for otitis media in children.

Zithromax has a long half-life (a measure of the time it stays active inside the human body), which allows for more convenient dosing. Patients may only need to take Zithromax once per day, and Pfizer markets Zithromax in prepackaged 3-day or 5-day courses, called a Z-Pak. The shorter and easier dosing schedule makes Zithromax a popular choice for both doctors and patients.

Zithromax Kidney Disorders

Though rare, cases of kidney dysfunction have been reported in association with Zithromax treatment. The current FDA-approved label for Zithromax notes some patients have reported interstitial nephritis and acute renal failure.

Interstitial nephritis is an inflammation of kidney tubules and the tissue that surrounds them. Drugs, such as Zithromax, are the most common cause of interstitial nephritis.

Symptoms of interstitial nephritis vary. When the condition develops quickly, the patient may experience changes in the amount of urine produced (either an increase or decrease). In cases where nephritis develops gradually, symptoms may include nausea, vomiting, fatigue, itchiness, or difficulty breathing.

Interstitial nephritis caused by a drug may resolve once the drug is stopped, but in some cases the condition progresses to cause damage that results in kidney failure, or the inability of the kidneys to adequately remove waste products from the blood. Kidney failure can also cause poor control of fluid balance, electrolytes, and levels of acidity in the blood. It may result in secondary conditions such as anemia, elevated blood pressure, and weakened bones.

When damage to the kidneys is irreversible, the resulting kidney failure may be chronic. Treatment in extreme cases of kidney failure may require dialysis or kidney transplantation.

A case report published in the Clinical Kidney Journal describes a case of acute interstitial nephritis that the authors believe could have been caused by azithromycin. The patient was a 16-year-old girl who showed up at the emergency room complaining of ten days’ worth of symptoms including vomiting, fatigue, malaise, and abdominal pain. She had not recently taken any pharmaceutical drugs other than a six-day course of azithromycin.

The report also mentions two earlier cases of interstitial nephritis possibly induced by azithromycin. One of those cases resulted in chronic renal failure after the patient’s second episode of acute interstitial nephritis. In the other case, the patient was still in need of hemodialysis ten months after acute interstitial nephritis began.