Paracetamol Toxicity

The answer first

Paracetamol (acetaminophen) remains a leading cause of severe acute liver injury. Mechanism papers from 1973 showed that hepatotoxicity is caused by a toxic intermediate epoxide metabolite normally detoxified by glutathione but which, in excess, binds covalently to hepatic enzymes and proteins. The clinical name for that metabolite is N-acetyl-p-benzoquinone imine (NAPQI). ^[7][17]

Three rules govern the long case. ^[7][11][3]

1. Treat from the clock and the concentration, not from how well the patient looks. Early recognition and prompt N-acetylcysteine (NAC) can prevent hepatic injury; the early phase is often silent. ^[17][2]
2. The Rumack-Matthew nomogram applies to a single acute immediate-release ingestion with a known time. Australia and New Zealand, with the United States, use a treatment line starting at 150 mg/L at 4 hours, extending to 24 hours with a half-life of 4 hours. The United Kingdom lowered that line to 100 mg/L at 4 hours for all patients in 2012 and ceased separate risk-factor lines. Staggered, repeated-supratherapeutic, modified-release, and unknown-time ingestions are not plotted — they are treated on clinical and biochemical grounds. ^[7][8][11]
3. Once acute liver failure is established, the question is transplant triage. O'Grady's acetaminophen cohort linked poor prognosis to arterial pH below 7.30, prothrombin time greater than 100 s, and creatinine greater than 300 micromol/L. Arterial lactate identifies non-survivors earlier than those King's College Hospital (KCH) criteria. Keep giving acetylcysteine — Keays showed it still improves survival after fulminant hepatic failure has declared itself. ^[3][5][4]

DCE trap: Name the ingestion pattern first. "Single acute, known time — plot the 4-hour level on the ANZ 150 mg/L line" is a different patient from "staggered over days — nomogram invalid, start NAC, consider early liver-centre transfer." ^[6][8][11]

---

References17ShowHide

1. [1]Prescott LF, Illingworth RN, Critchley JA, Stewart MJ, et al. Intravenous N-acetylcystine: the treatment of choice for paracetamol poisoning Br Med J, 1979.PMID 519312
2. [2]Smilkstein MJ, Knapp GL, Kulig KW, Rumack BH Efficacy of oral N-acetylcysteine in the treatment of acetaminophen overdose. Analysis of the national multicenter study (1976 to 1985) N Engl J Med, 1988.PMID 3059186
3. [3]O'Grady JG, Alexander GJ, Hayllar KM, Williams R Early indicators of prognosis in fulminant hepatic failure Gastroenterology, 1989.PMID 2490426
4. [4]Keays R, Harrison PM, Wendon JA, Forbes A, et al. Intravenous acetylcysteine in paracetamol induced fulminant hepatic failure: a prospective controlled trial BMJ, 1991.PMID 1954453
5. [5]Bernal W, Donaldson N, Wyncoll D, Wendon J Blood lactate as an early predictor of outcome in paracetamol-induced acute liver failure: a cohort study Lancet, 2002.PMID 11867109
6. [6]Craig DG, Bates CM, Davidson JS, Martin KG, et al. Staggered overdose pattern and delay to hospital presentation are associated with adverse outcomes following paracetamol-induced hepatotoxicity Br J Clin Pharmacol, 2012.PMID 22106945
7. [7]Bateman DN, Dart RC, Dear JW, Prescott LF, et al. Fifty years of paracetamol (acetaminophen) poisoning: the development of risk assessment and treatment 1973-2023 with particular focus on contributions published from Edinburgh and Denver Clinical Toxicology (Philadelphia), 2023.PMID 38197864
8. [8]Bateman DN, Carroll R, Pettie J, Yamamoto T, et al. Effect of the UK's revised paracetamol poisoning management guidelines on admissions, adverse reactions and costs of treatment Br J Clin Pharmacol, 2014.PMID 24666324
9. [9]Bateman DN, Dear JW, Carroll R, Pettie J, et al. Impact of reducing the threshold for acetylcysteine treatment in acute paracetamol poisoning: the recent United Kingdom experience Clin Toxicol (Phila), 2014.PMID 25200454
10. [10]Yarema M, Chopra P, Sivilotti MLA, Johnson D, et al. Anaphylactoid Reactions to Intravenous N-Acetylcysteine during Treatment for Acetaminophen Poisoning J Med Toxicol, 2018.PMID 29423816
11. [11]Chiew AL, Reith D, Pomerleau A, Wong A, et al. Updated guidelines for the management of paracetamol poisoning in Australia and New Zealand Med J Aust, 2020.PMID 31786822
12. [12]Chyka PA, Seger D, Krenzelok EP, Vale JA, et al. Position paper: Single-dose activated charcoal Clin Toxicol (Phila), 2005.PMID 15822758
13. [13]Rumack BH, Peterson RC, Koch GG, Amara IA Acetaminophen overdose. 662 cases with evaluation of oral acetylcysteine treatment Arch Intern Med, 1981.PMID 7469629
14. [14]Bateman DN, Dear JW, Thomas SH New regimens for intravenous acetylcysteine, where are we now? Clin Toxicol (Phila), 2016.PMID 26666290
15. [15]Dart RC, Mullins ME, Matoushek T, Ruha AM, et al. Management of Acetaminophen Poisoning in the US and Canada: A Consensus Statement JAMA Netw Open, 2023.PMID 37552484
16. [16]Schmidt LE, Rasmussen DN, Petersen TS, Macias-Perez IM, et al. Fewer adverse effects associated with a modified two-bag intravenous acetylcysteine protocol compared to traditional three-bag regimen in paracetamol overdose Clin Toxicol (Phila), 2018.PMID 29792347
17. [17]Hodgman MJ, Garrard AR A review of acetaminophen poisoning Crit Care Clin, 2012.PMID 22998987