Interstitial nephritis is a kidney disorder in which the spaces between the kidney tubules become swollen (inflamed). The inflammation can affect the kidneys' function, including their ability to filter waste.

Tubulointerstitial nephritis; Nephritis - interstitial; Acute interstitial (allergic) nephritis

Interstitial nephritis may be temporary (acute) or it may be long-lasting ( chronic) and get worse over time.

The following can cause interstitial nephritis:

• Allergic reaction to a drug (acute interstitial allergic nephritis)
• Analgesic nephropathy
• Long-term use of medications such as acetaminophen (Tylenol), aspirin, and nonsteroidal anti-inflammatory drugs (NSAIDS). This is called analgesic nephropathy
• Side effect of certain antibiotics (penicillin, ampicillin, methicillin, sulfonamide medications, and others)
• Side effect of medications such as NSAIDs, furosemide, and thiazide diuretics

The acute form of interstitial nephritis is common. It is most often caused by side effects of certain drugs. This disorder may be more severe and more likely to lead to chronic or permanent kidney damage in elderly people.

Interstitial nephritis can cause mild to severe kidney problems, including acute kidney failure. In about half of cases, people will have decreased urine output and other signs of acute kidney failure.

Symptoms of this condition may include:

• Blood in the urine
• Fever
• Increased or decreased urine output
• Mental status changes (drowsiness, confusion, coma)
• Nausea, vomiting
• Rash
• Swelling of the body, any area
• Weight gain (from retaining fluid)

An exam may show too much fluid under the skin or in the lungs (peripheral or pulmonary edema). The health care provider might hear abnormal sounds when listening to the heart or lungs with a stethoscope (auscultation). High blood pressure is common.

Common tests include:

• Arterial blood gases
• Blood chemistry
• BUN and blood creatinine levels
• Complete blood count
• Kidney biopsy
• Urinalysis
• Urine osmolality

Treatment focuses on the cause of the problem. Avoiding medications that lead to this condition may relieve the symptoms quickly.

Limiting salt and fluid in the diet can improve swelling and high blood pressure. Limiting protein in the diet can help control the buildup of waste products in the blood (azotemia) that can lead to symptoms of acute kidney failure.

If dialysis is necessary, it usually is required for only a short time.

Corticosteroids or anti-inflammatory medications can help in some cases.

Most often, interstitial nephritis is a short-term disorder. In rare cases, it can cause permanent damage, including chronic kidney failure.

Metabolic acidosis can occur because the kidneys aren't able to remove enough acid. The disorder can lead to acute or chronic kidney failure or end-stage kidney disease.

Call your health care provider if you have symptoms of interstitial nephritis.

If you have interstitial nephritis, call your health care provider if you get new symptoms, especially if you are less alert or have a decrease in urine output.

In many cases, the disorder can't be prevented. Avoiding or reducing your use of medications that can cause this condition can help reduce your risk.