Acute interstitial nephritis classically presents with fever, maculopapular rash, eosinophilia, eosinophiluria, and urinary WBC casts. Eosinophiluria is neither sensitive (sensitivity 40%) nor entirely specific (specificity 72%, positive predictive value 38%). The classic triad of rash, fever and eosinophilia is actually uncommon and only seen approximately 10% of the time. One can also see mild proteinuria (usually < 1g/d) and other signs of tubular damage, such as renal tubular acidosis and Fanconi’s syndrome. Renal ultrasound generally reveals kidneys of normal to large size. Gallium scanning has been suggested as an aid to distinguishing this condition from acute tubular necrosis (ATN). It is negative in ATN but generally positive in interstitial nephritis.
Drug classes that can cause AIN:
Penicillin analogs (methicillin, ampicillin, etc.)– most common
Cephalosporins
Sulfonamides (sulfamethoxazole,cotrimoxazole)
Other antibiotics such as rifampin andciprofloxacin
NSAIDS (including Cox-2 specific agents)
Diuretics
Proton pump inhibitors
Miscellaneous – this includes a very largenumber of drugs such as allopurinol and cimetidine.
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