NAC protocol
Formal Definition
N-acetylcysteine (NAC) administration protocol used to treat acetaminophen (APAP) overdose; NAC replenishes glutathione, preventing hepatotoxic NAPQI accumulation; administered IV (21-hour three-bag protocol) or orally (72-hour protocol); efficacy is highest within 8–10 hours of ingestion but can reduce liver failure even in late presentations.
How It's Used on the Ward
"Starting NAC" or "NAC protocol is running" — the antidote protocol for APAP overdose that is the cornerstone of preventing liver failure.
Example
""4-hour serum APAP level of 280 mcg/mL — plots above the Rumack-Matthew nomogram treatment line. Starting IV NAC: 150 mg/kg loading dose over 60 minutes, then 12.5 mg/kg/hr for 4 hours, then 6.25 mg/kg/hr for 16 hours. LFTs every 8 hours.""
Clinical Context
Rumack-Matthew nomogram: plot serum APAP level against time since ingestion (for single acute ingestion). Treatment indicated if above nomogram line. IV protocol: three bags — 150 mg/kg over 1h (loading), 50 mg/kg over 4h, 100 mg/kg over 16h. Most common NAC adverse effect: anaphylactoid reaction (flushing, urticaria, bronchospasm) — not true allergy, slow infusion, treat with diphenhydramine. Send APAP on ALL suspected overdoses — patients often do not disclose APAP ingestion, and the window for effective treatment is narrow. Late presentation (>24h with elevated INR and AST) still benefits from NAC.