## Management of Paracetamol Overdose ### Timing and Nomogram Interpretation **Key Point:** The Rumack-Matthew nomogram guides NAC initiation based on serum paracetamol level and time since ingestion. At 2 hours post-ingestion with a level of 180 µg/mL, this patient falls in the **high-risk zone** and requires immediate antidote therapy. ### Why NAC is the Correct Answer **High-Yield:** NAC is most effective when started within 8–10 hours of ingestion but can be beneficial up to 24 hours if hepatotoxicity has not yet developed. At 2 hours with a level above the nomogram threshold, immediate IV NAC initiation is the standard of care. **Clinical Pearl:** NAC works by: 1. Replenishing hepatic glutathione stores 2. Conjugating toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI) 3. Preventing hepatocellular necrosis ### Nomogram Reference | Time (hours) | High-Risk Level | Low-Risk Level | |---|---|---| | 4 | 200 µg/mL | 150 µg/mL | | 8 | 100 µg/mL | 75 µg/mL | | 12 | 50 µg/mL | 37.5 µg/mL | | 16 | 25 µg/mL | 18.75 µg/mL | At 2 hours with 180 µg/mL, this patient is **above the high-risk line** and requires NAC. ### Standard NAC Regimen (IV) 1. **Loading dose:** 150 mg/kg over 1 hour 2. **Second dose:** 50 mg/kg over 4 hours 3. **Third dose:** 100 mg/kg over 16 hours **Warning:** Oral methionine is an older antidote (now rarely used) and is less effective than NAC. Do not delay NAC for methionine. [cite:Harrison 21e Ch 468]
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