Among the beta-lactam antibiotics, which is the most common cause of drug-induced acute interstitial nephritis (AIN) in clinical practice?

Explanation

## Most Common Cause of Beta-Lactam–Induced AIN **Key Point:** Amoxicillin is the most frequently reported beta-lactam antibiotic causing drug-induced acute interstitial nephritis, particularly when given in high doses or for prolonged durations. ### Mechanism of AIN in Beta-Lactams Beta-lactam antibiotics, especially aminopenicillins (amoxicillin, ampicillin), trigger AIN through: 1. **Hapten formation** — the drug or its metabolite binds to renal tubular epithelial cells 2. **Type IV hypersensitivity** — T-cell mediated immune response against the drug-cell complex 3. **Antibody formation** — IgE and IgG antibodies against the penicilloyl hapten ### Why Amoxicillin Leads **High-Yield:** Amoxicillin accounts for approximately **30–40% of all drug-induced AIN cases** in most series, making it the single most common beta-lactam culprit. This is due to: - Widespread use in primary care and outpatient settings - Frequent high-dose regimens (especially for respiratory and UTI infections) - Greater immunogenicity of the aminopenicillin side chain compared to other beta-lactams ### Clinical Presentation of Beta-Lactam–Induced AIN **Clinical Pearl:** Classic triad occurs 1–3 weeks after drug initiation: - Fever (often low-grade) - Rash (maculopapular, sometimes urticarial) - Acute kidney injury (elevated creatinine, oliguria) **Warning:** Eosinophiluria and eosinophilia are present in only ~50% of cases — absence does not exclude AIN. ### Comparative Frequency Among Beta-Lactams | Beta-Lactam Class | Relative AIN Risk | Frequency | |---|---|---| | Aminopenicillins (amoxicillin, ampicillin) | Highest | Most common | | Antipseudomonal penicillins (azlocillin, piperacillin) | Moderate | Less common | | Cephalosporins (ceftriaxone, cefadroxil) | Lower | Rare | | Carbapenems | Lowest | Very rare | **Mnemonic:** **PENICILLIN-AIN** = **P**enicillins (esp. **A**mino-) cause **I**nterstitial **N**ephritis most often among beta-lactams. ### Management 1. **Immediate:** Discontinue the offending agent 2. **Supportive:** Fluid management, electrolyte correction 3. **Corticosteroids:** Consider if severe (creatinine >2× baseline or oliguria) — short course of prednisolone 0.5–1 mg/kg/day for 1–2 weeks may accelerate recovery 4. **Monitoring:** Renal function typically recovers within 1–3 months post-discontinuation [cite:KD Tripathi 8e Ch 50]