Acute Interstitial Nephritis (AIN)

Acute Interstitial Nephritis (AIN) is a form of kidney inflammation primarily affecting the renal interstitium and tubules, often leading to acute kidney injury. The disease typically arises as a hypersensitivity reaction to medications such as antibiotics, proton pump inhibitors, and nonsteroidal anti-inflammatory drugs. Less commonly, it results from infections or autoimmune conditions like sarcoidosis and Sjögren’s syndrome. Histologically, AIN is characterized by infiltration of inflammatory cells—mainly lymphocytes, plasma cells, and eosinophils—within the renal interstitium, causing edema and tubular injury.

Clinically, patients may present with reduced urine output, fatigue, rash, fever, and blood or protein in urine. The classic triad of rash, fever, and eosinophilia occurs infrequently. Diagnosis is suggested by elevated creatinine levels and confirmed by kidney biopsy showing interstitial inflammation. Management involves prompt withdrawal of the offending drug or treatment of the underlying cause, along with corticosteroids in selected cases to hasten recovery. Most individuals experience partial renal function recovery, but delayed diagnosis may lead to chronic interstitial fibrosis or permanent renal impairment. Early recognition and intervention are essential for favorable outcomes in AIN.?