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

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

The following can cause interstitial nephritis:

• Allergic reaction to a drug (acute interstitial allergic nephritis)
• Analgesic nephropathy
• Side effect of certain antibiotics (penicillin, ampicillin, methicillin, sulfonamide medications, and others)
• Side effect of medications such as nonsteroidal anti-inflammatory drugs (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 include:

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

An exam may show edema or too much fluid. The health care provider might hear abnormal sounds when listening to the heart or lungs with a stethoscope (auscultation). Blood pressure commonly is high.

Common tests include:

• Arterial blood gases and blood chemistry
• BUN and creatinine levels
• Complete blood count
• Kidney biopsy
• Red blood cell count - urine
• Urinalysis
• Urine pH
• Urine specific gravity and osmolality
• White blood cell count