PE14.3 | Paracetamol Poisoning — Summary & Reflection

KEY TAKEAWAYS

Paracetamol poisoning — key take-home points:

• Paracetamol is metabolised to NAPQI by CYP2E1; NAPQI is normally detoxified by glutathione, but in overdose (>150 mg/kg in children) glutathione is depleted and NAPQI accumulates → centrilobular hepatic necrosis.

• Four clinical phases: Phase I (nausea, 0–24 h) → Phase II (apparent recovery, rising transaminases — the deceptive phase, 24–72 h) → Phase III (fulminant hepatic failure, 72–96 h) → Phase IV (recovery or death).

• Treatment decision is guided by the Rumack-Matthew nomogram — plasma paracetamol level at ≥4 hours post-ingestion plotted against time. Level above the treatment line → start NAC.

• Antidote: N-acetylcysteine (NAC) — replenishes glutathione, most effective within 8–10 hours but given up to 24 hours and beyond in established hepatotoxicity. IV protocol: 150 mg/kg/1h → 50 mg/kg/4h → 100 mg/kg/16h (all doses weight-based).

• Activated charcoal (1 g/kg) if presented within 1 hour of ingestion.

• Do NOT wait for symptoms before starting NAC — Phase II apparent recovery is the worst time to be falsely reassured.

REFLECT

Return to the hook case: a 13-year-old girl who ingested approximately 143 mg/kg of paracetamol, looks well, and whose mother says 'she looks fine, doctor.' This is a classic Phase I presentation. The correct answer is not to discharge, not to observe for 6 hours on clinical appearance alone, but to draw a plasma paracetamol level immediately, plan a 4-hour level for nomogram plotting, and admit for monitoring. If the nomogram level is above the treatment line, start NAC that night. The girl's apparent wellness is not reassuring — it is part of the natural history. Reflect on the emotional complexity of this case: the adolescent who is ambivalent about whether she wanted to harm herself, the mother who is relieved and wants to go home, and you as the physician who must hold the clinical boundary while still being compassionate. How do you communicate the seriousness of delayed hepatotoxicity to a family who sees a healthy child in front of them? How do you balance the adolescent's need for psychiatric assessment with the urgent medical intervention required?