A 56-year-old man with no known medical history was treated with piperacillin–tazobactam for polymicrobial osteomyelitis and developed acute renal failure with fever and rash after six weeks of therapy. A gallium scan showed mildly increased uptake of radioactive tracer in both kidneys diffusely. A renal ultrasound showed normalsized kidneys without hydronephrosis. Urinalysis revealed eosinophils 5–25% (normal, <1%), hyaline casts, white blood cells, and proteinuria (>1000 mg/dL; normal range, 0–30 mg/dL). He received dialysis and was treated with empirical corticosteroids for acute interstitial nephritis (AIN). The patient’s hospital course was complicated by nosocomial infections requiring treatment with meropenem. After receiving meropenem, the patient developed worsening renal function and a rash that abated after the discontinuation of meropenem, indicating possible cross-sensitivity with piperacillin–tazobactam. AIN can be caused by autoimmune disorders, infections, sarcoidosis, or medications.1,–5 Many drugs (e.g., methicillin, cephalosporins, rifampin, ciprofloxacin, sulfonamides, nonsteroidal antiinflammatory drugs, cimetidine, omeprazole, indinavir) have been reported to cause drug-induced AIN.5,6 Drug-induced AIN is believed to be a hypersensitivity reaction.1 The diagnosis of AIN is usually made by examining the patient’s history, the temporal relation between the onset of AIN and initiation of the offending agent, the presence of certain clinical features and certain laboratory test findings, the exclusion of alternative causes of acute renal failure, a renal biopsy, and an empirical trial with corticosteroids.6
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