Snapshot A 65-year-old man presents to urgent care with a sudden-onset of fever and rash. His review of systems is negative. He was recently started on omeprazole for acid reflux approximately 2 weeks ago. Routine laboratory tests reveal a serum creatinine of 3.5 mg/dL and eosinophilia. Urine studies showed white blood cell casts. Introduction Clinical definition acute interstitial nephritis (AIN), also known as tubulointerstitial nephritis, is an acute immune-mediated interstitial inflammation of the kidneys Epidemiology demographics male:female ratio is 3:1 in methicillin-induced AIN 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 mycoplasma autoimmune diseases systemic lupus erythematosus sarcoidosis Pathogenesis type IV hypersensitivity reaction T-cell-mediated attack on tubular cells Presentation Symptoms primary symptoms fever minimal hematuria flank pain arthralgias can be asymptomatic defining characteristics development of rash after administration of drug Physical exam rash diffuse 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 recall that urinalysis can only detect white blood cells, red blood cells, and protein most accurate test Renal biopsy not usually indicated indications patients with suspected AIN but no obvious etiology only definitive method of diagnosis 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, 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 if etiology is sarcoidosis Complications Renal failure requiring dialysis Prognosis typically resolves after withdrawal of inciting agent