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.

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.