Snapshot A 60-year-old man presents to the emergency room with a 1-day history of fever and a new skin rash. He is taking methicillin for a soft tissue infection. On physical exam, he has costovetebral tenderness, and a diffuse maculopapular rash over his trunk. His serum creatinine is elevated at 3 mg/dL. Urinalysis reveals white blood cells. Further testing with Wright stain is positive for eosinophils in the urine. Introduction Clinical definition acute interstitial nephritis (AIN), also known as tubulointerstitial nephritis, is an acute immune-mediated interstitial inflammation of the kidneys Epidemiology demographics middle-aged adults Etiology drug-induced hypersensitivity (majority of cases) typically developed between 1 week to 9 months 5 Ps Pee (diuretics, especially sulfa ones) Pain-free (NSAIDs) Penicillins and cephalosporins Proton pump inhibitors rifamPin systemic infections autoimmune diseases systemic lupus erythematosus sarcoidosis Pathogenesis type IV hypersensitivity reaction T-cell-mediated attack on tubular cells Prognosis typically resolves after withdrawal of inciting agent Presentation Symptoms primary symptoms fever hematuria arthralgia can be asymptomatic Physical exam rash maculopapular flank/costovertebral angle tenderness Studies Labs serum eosinophilia elevated serum creatinine Urinalysis with microscopy and sediment analysis white blood cell casts hematuria eosinophiluria seen with Hansel or Wright stain Renal biopsy not usually indicated Histology severe tubular damage interstitial edema T-cell and eosinophilic infiltration Diagnostic criteria elevated creatinine urinalysis with white cell casts and eosinophiluria Differential Acute tubular necrosis from NSAIDs no rash or eosinophils Renal atheroemboli also presents with eosinophiluria, eosinophilia, and skin rash rash is typically livedo reticularis with digital infarcts and not maculopapular Treatment Conservative discontinue inciting drug indications for all drug-induced hypersensitivity cases Medical glucocorticoids indications if creatinine continues to rise after stopping drugs Complications Renal failure requiring dialysis