Interstitial nephritis involves inflammation of the spaces between the renal (kidney) tubules and may include inflammation of the tubules. It may be temporary, most often associated with the effects of various drugs on the kidney, or it may be chronic and get progressively worse. Interstitial nephritis is associated with analgesic nephropathy, and can also occur with allergic reaction to a drug (acute interstitial allergic nephritis) or as a side effect of medications such as antibiotics (penicillin, ampicillin, methicillin, sulfonamide medications, and others). Other medications include nonsteroidal anti-inflammatory drugs (NSAIDs), furosemide, and thiazide diuretics. The disorder may occur 2 or more weeks after exposure to the medication. Interstitial nephritis causes mild to severe kidney function, including acute kidney failure. In about half of cases, patients will have decreased urine output and other signs of acute kidney failure. The kidney may fail to concentrate the urine when water intake is reduced. The kidney may fail to regulate acid/base levels of the body, with failure to excrete acid appropriately in the urine. Metabolic acidosis may occur because of the inability to excrete acid. The disorder may progress to chronic kidney failure or end-stage renal (kidney) disease. The acute form of interstitial nephritis is common and may account for approximately 15% of cases of acute kidney failure. Risks include exposure to medications that may be toxic to the kidneys. The disorder may be more severe and more likely to lead to chronic or permanent kidney damage in the elderly.
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