Acute Interstitial Nephritis (AIN)

Acute interstitial nephritis (AIN) is an inflammatory disorder affecting the kidney interstitium and tubules. The interstitium is the supporting tissue between the tubules, and the tubules do the fine work of reclaiming sodium, handling potassium and excreting acid. AIN is an important potentially reversible cause of intrinsic acute kidney injury (AKI). The word "potentially" carries the nursing weight: inflammation that is recognized and removed early can settle, while inflammation left in place can scar. Medications are the most common cause, estimated at more than 70% of AIN in high-income countries. Antibiotics account for nearly half of drug-related cases and NSAIDs for roughly 10–15%, and proton pump inhibitors (PPIs) and immune checkpoint inhibitors are also leading causes. The remaining cases come from infection-associated inflammation, autoimmune disease and other systemic inflammatory disorders. Drug-related AIN does not behave like a dose-related toxin. It is a hypersensitivity or immune-mediated reaction, so it can follow an ordinary dose of a medication the patient has tolerated for months. ### From trigger to kidney injury Follow the chain, because each link explains a finding: 1. Medication exposure,...