Suspected paracetamol (acetaminophen) poisoning
Adults and children: deliberate overdose, accidental ingestion or excess use for pain or fever
All Pathways
Emergency MedicineEmergency
Paracetamol (Acetaminophen) Poisoning Management
Paracetamol (Acetaminophen) Poisoning Management: Suspected paracetamol (acetaminophen) poisoning → Time-critical: start acetylcysteine within 8 h of in...
Pathway Overview
22 steps
Algorithm Steps
22 total
01Start 02Warning Time-critical: start acetylcysteine within 8 h of ingestion
Poisons Information Centre 13 11 26 (AU), 0800 764 766 (NZ), 1-800-222-1222 (US)
- Already over 8 h, or the level will not be back by 8 h: start acetylcysteine now
- Modified-release 10 g or 200 mg/kg or more (whichever is less): start now; the nomogram does not apply
- IV paracetamol error, neonate, 50 g or 1 g/kg or more, or level over 3 times the line: get toxicology advice
03Action Risk assessment
Deliberate overdose: measure a paracetamol level whatever the stated dose
- Dose (g and mg/kg) and time of first ingestion
- Toxic acute dose: 10 g or 200 mg/kg or more, whichever is less
- Formulation: immediate-release, modified-release (665 mg), liquid or IV
- Pattern: single or staggered self-harm, or repeated use for pain or fever
- Co-ingested opioid or anticholinergic; body weight; pregnancy (same thresholds and treatment)
- History unreliable or time unknown: manage as unknown time
04Action Initial tests
Check the units: 150 mg/L = 1000 µmol/L; 10 mg/L = 66 µmol/L
- Paracetamol level 4 h or more after ingestion (a level before 4 h cannot be plotted)
- ALT (and AST), creatinine and electrolytes, glucose
- INR and venous gas with lactate if late presentation, ALT raised, liver injury suspected, large ingestion or reduced consciousness
- No paracetamol or ALT test on site: possible toxic dose or any symptoms: start acetylcysteine; call Poisons Information Centre. Transfer to a hospital with pathology if symptoms, 30 g or 500 mg/kg or more, modified-release 10 g or 200 mg/kg or more (give charcoal too), or acetylcysteine started over 8 h after ingestion
- Pregnancy test in women of childbearing age
05Warning Liver injury at presentation: act now, do not wait 20 h
ALT above 1000 U/L, INR raised, encephalopathy, acidosis or hypoglycaemia (often late presentation)
- Start IV acetylcysteine now; do not wait for the paracetamol level
- Check the liver transplant unit referral criteria now (step 'Liver transplant unit referral criteria met?')
- Call a clinical toxicologist or Poisons Information Centre; discuss early with the liver transplant unit
06Decision Type of ingestion?
Acute immediate-release with known time; modified-release; repeated use for pain or fever; or unknown time, unreliable history or over 24 h
- Acute immediate-release, known time
07Action Acute immediate-release ingestion, known time
Any deliberate ingestion within 24 h. Staggered doses: use the time of the first dose; if the first level is within 2 h of the last dose, repeat it 2 h later.
- Up to 8 h: level (and ALT) at 4-8 h; plot on nomogram (line 150 mg/L at 4 h)
- 8-24 h: start acetylcysteine now; stop if level below the line and ALT 50 U/L or less
- On or above the line: full acetylcysteine course; more than double the line: increased dose
- Opioid or anticholinergic co-ingestion, level above 10 mg/L but below the line: repeat in 4-6 h
- Well child under 6 y, liquid only, over 200 mg/kg: level at 2 h or later; 150 mg/L or more: repeat at 4 h
08Action Activated charcoal: awake, cooperative patient only
Not if consciousness is reduced or the airway is at risk. Not for repeated supratherapeutic ingestion. Child: get Poisons Information Centre advice first.
- Adult: activated charcoal 50 g orally
- Immediate-release toxic dose: within 2 h (US/Canada: consider within 4 h)
- Immediate-release 30 g or more, or modified-release toxic dose: up to 4 h
- Modified-release 30 g or 500 mg/kg or more: may help after 4 h; get toxicology advice
09Decision Acetylcysteine indicated?
Yes if any: level on or above the nomogram line; 8-24 h and ALT above 50 U/L; modified-release toxic dose; repeated-ingestion or unknown-time criteria met; level still pending at 8 h. Started before the level: stop only if below the line and ALT 50 U/L or less.
- If Yes
10Action Indicated: IV acetylcysteine, two-bag regimen (20 h)
Acetylcysteine injection 200 mg/mL (e.g., 2 g in 10 mL). Anaphylactoid reaction (mostly in Bag 1): pause the infusion, give an antihistamine (bronchodilator if wheeze) and supportive care, then restart at a slower rate. Do not stop the course.
- Bag 1: 200 mg/kg (max 22 g) IV over 4 h in 500 mL glucose 5% or sodium chloride 0.9%
- Bag 2: 100 mg/kg (max 11 g) IV over 16 h in 1000 mL
- Age 14 y and over: actual weight rounded up to the nearest 10 kg, max 110 kg (US/Canada: cap 100 kg)
- Child under 14 y: actual weight; volumes 7 mL/kg (max 500 mL), then 14 mL/kg (max 1000 mL)
- Pulse oximetry for the first 2 h; asthma raises the reaction risk. Vomiting: adjust the rate and continue
- Gives 300 mg/kg over 20 h (ANZ 2020). Other regimens (US): at least 300 mg/kg in 20-24 h; 150 mg/kg loading dose over at least 1 h
11Warning High-risk ingestion: increase acetylcysteine
Level more than double the nomogram line, or modified-release 30 g or 500 mg/kg or more
- Bag 2: 200 mg/kg (max 22 g) IV over 16 h instead of 100 mg/kg
- Immediate-release 30 g or more, level over 3 times the line, or 50 g or 1 g/kg or more: call a clinical toxicologist
- Paracetamol 900 mg/L or more with acidosis or reduced consciousness: haemodialysis plus acetylcysteine (IV at least 12.5 mg/kg/h during dialysis)
12Action Before Bag 2 ends: repeat tests
About 2 h before the infusion ends. Do not stop at 20 h without these results.
- Paracetamol level, ALT (and AST) and INR
- Glucose, creatinine and electrolytes
- ALT above 1000 U/L: add phosphate and venous gas (pH, lactate); call a clinical toxicologist
- Watch for abdominal pain, nausea, vomiting and right upper quadrant tenderness
13Decision Stopping criteria met?
All of: paracetamol below 10 mg/L (66 µmol/L); ALT normal, or falling from its peak; INR below 2.0; patient clinically well. Small ALT changes (about 20 U/L or 10%) alone do not need more acetylcysteine.
- If Yes
14Outcome Criteria met: stop acetylcysteine
Mental health assessment before discharge if deliberate. Advise return if abdominal pain, nausea or vomiting.
If No15Action Criteria not met: continue acetylcysteine
- Continue at the same rate as Bag 2 (e.g., 100 mg/kg over 16 h). Massive ingestion: a higher rate (e.g., 200 mg/kg over 16 h) may be needed; call a clinical toxicologist
- Repeat paracetamol level, ALT and INR at least every 12 h
- Paracetamol 100 mg/L (660 µmol/L) or more at the end of the 20-h course: a higher rate may be needed; call a clinical toxicologist
- ALT above 1000 U/L: call a clinical toxicologist or Poisons Information Centre
16Decision Liver transplant unit referral criteria met?
Any of: INR above 3.0 at 48 h or above 4.5 at any time; oliguria or creatinine above 200 µmol/L; pH below 7.3 or arterial lactate above 3 mmol/L; SBP below 80 mmHg despite resuscitation; hypoglycaemia; severe thrombocytopenia; encephalopathy or GCS below 15 not due to sedatives
- If Yes
17Warning Liver failure risk: call the liver transplant unit now
Discuss early and arrange transfer
- Continue acetylcysteine
- Do not give clotting factors unless bleeding or advised by the liver unit
- Monitor glucose, INR, creatinine, pH and lactate closely
18Outcome Liver transplant unit care
Transfer to a liver transplant centre
If No- No: recheck
- Path rejoins step 13Shared downstream outcome
If No19Outcome Below treatment criteria: no acetylcysteine
Stop acetylcysteine if already started. Mental health assessment if deliberate. Advise return if abdominal pain, nausea or vomiting. Raised ALT with a level below the line: review the history.
- Modified-release
20Action Modified-release paracetamol (e.g., 665 mg tablets)
Absorption can be delayed; the nomogram must not be used to decide treatment
- 10 g or 200 mg/kg or more (whichever is less): start acetylcysteine now; full 20-h course whatever the level
- Two levels for all: first 4 h or more after ingestion, second 4 h later. Below 10 g and below 200 mg/kg: full course if either is above the line
- 30 g or 500 mg/kg or more, or either level more than double the line: increased dose
- Levels static or rising, or 50 g or 1 g/kg or more: get toxicology advice
- Path rejoins step 08Shared downstream outcome
- Repeated supratherapeutic
21Action Repeated supratherapeutic ingestion (use for pain or fever)
Nomogram does not apply. No charcoal. Any symptoms (abdominal pain, nausea, vomiting): assess.
- Assess if 10 g or 200 mg/kg or more in 24 h, or 12 g or 300 mg/kg or more in 48 h (whichever is less), or at least a daily therapeutic dose for over 48 h with abdominal pain, nausea or vomiting
- Measure paracetamol level and ALT: acetylcysteine if paracetamol above 20 mg/L (132 µmol/L) or ALT above 50 U/L
- Repeat both 8 h after the first sample: stop if paracetamol below 10 mg/L and ALT below 50 U/L or static
- ALT above 1000 U/L: complete a 20-h course and call a clinical toxicologist
- Path rejoins step 09Shared downstream outcome
- Unknown time, unreliable or over 24 h
22Action Unknown time, unreliable history, or presents over 24 h
Nomogram cannot be used. If in doubt, give acetylcysteine.
- Start acetylcysteine while waiting for results
- Measure paracetamol level and ALT (and AST)
- Continue if paracetamol 10 mg/L (66 µmol/L) or more, or ALT above 50 U/L
- Stop if paracetamol below 10 mg/L and ALT 50 U/L or less
- Path rejoins step 09Shared downstream outcome
Guideline Source
Updated guidelines for the management of paracetamol poisoning in Australia and New Zealand (Chiew AL et al., MJA 2020); Management of Acetaminophen Poisoning in the US and Canada: A Consensus Statement (Dart RC et al., JAMA Netw Open 2023)
Clinical Safety Information
Clinical Decision Support — Not a Substitute for Clinical Judgment
Individual patient factors may require deviation from these recommendations.
Known Limitations
- Nomogram only for acute oral immediate-release ingestion with a known time (not modified-release, repeated or IV paracetamol)
- Massive, modified-release or complex cases: get toxicology advice (Poisons Information Centre 13 11 26 in AU)
- Two-bag regimen per ANZ 2020; US/Canada accepts any regimen giving at least 300 mg/kg in 20-24 h
- Neonatal exposure and IV paracetamol errors need toxicology advice
Contraindicated Populations
Neonates (get toxicology advice)IV paracetamol overdose or dosing error (nomogram not valid)
Applicable Regions
AUNZUS
AU: ANZ 2020 guideline; IV acetylcysteine. Poisons Information Centre 13 11 26. Modified-release 665 mg tablets are a common overdose.
EU: UK practice differs (MHRA 2012: treatment line 100 mg/L at 4 h). Follow national guidance.
NZ: ANZ 2020 guideline. National Poisons Centre 0800 764 766.
US: US/Canada consensus 2023: any published IV or oral regimen giving at least 300 mg/kg in 20-24 h; dose weight capped at 100 kg. 8-hour extended-release products: if a 4-12 h level is below the line but above 10 mcg/mL, repeat it 4-6 h later. Poison control 1-800-222-1222.
Version 2Next review: 2027-09-30
Next steps
Finish the workflow by opening the most relevant calculator, then convert the session into a live account when you are ready.
Related Resources
Frequently Asked Questions
What is the Paracetamol (Acetaminophen) Poisoning Management?
The Paracetamol (Acetaminophen) Poisoning Management is a emergency clinical algorithm for Emergency Medicine. It provides a structured decision tree to guide clinical decision-making, based on Updated guidelines for the management of paracetamol poisoning in Australia and New Zealand (Chiew AL et al., MJA 2020); Management of Acetaminophen Poisoning in the US and Canada: A Consensus Statement (Dart RC et al., JAMA Netw Open 2023).
What guideline is the Paracetamol (Acetaminophen) Poisoning Management based on?
This algorithm is based on Updated guidelines for the management of paracetamol poisoning in Australia and New Zealand (Chiew AL et al., MJA 2020); Management of Acetaminophen Poisoning in the US and Canada: A Consensus Statement (Dart RC et al., JAMA Netw Open 2023) (DOI: 10.5694/mja2.50428).
What are the limitations of the Paracetamol (Acetaminophen) Poisoning Management?
Known limitations include: Nomogram only for acute oral immediate-release ingestion with a known time (not modified-release, repeated or IV paracetamol); Massive, modified-release or complex cases: get toxicology advice (Poisons Information Centre 13 11 26 in AU); Two-bag regimen per ANZ 2020; US/Canada accepts any regimen giving at least 300 mg/kg in 20-24 h; Neonatal exposure and IV paracetamol errors need toxicology advice. Individual patient factors may require deviation from these recommendations.
Get AI-Powered Analysis Alongside This Algorithm
In AttendMe.ai, the Paracetamol (Acetaminophen) Poisoning Management appears automatically when your clinical question matches — alongside evidence from 3M+ peer-reviewed articles.
Try AttendMe Free