EMed

Paracetamol overdose Adults

These guidelines relate to adult patients only. For paediatric patients please use "Paracetamol XS Paediatrics" and discuss with your EM senior.

Please note a different NAC regimen for adults <kg.

Background

  • Hepatocellular necrosis is the major toxic effect
  • Biochemical evidence of max. damage may not be until 72 - 96 hours post ingestion
  • At risk dose is > 75mg paracetamol/kg body weight
  • Severe liver damage = peak ALT > 1000 u/L
  • Presentations > 12 hours post ingestion are more severely poisoned and at greater risk
  • Acute renal tubular necrosis may also occur
  • If there is doubt about the timing or the need for treatment - treat
  • Methionine is ineffective in those given activated charcoal
  • NAC is the treatment of choice>

High risk patients

  • Regular alcohol ingestion
  • Other enzyme (liver oxidase) inducers (e.g. carbamazepine, phenytoin, phenobarbitone, primidone and rifampicin)
  • Glutathione depletion (e.g. malnutrition and HIV)

Do NOT take plasma levels within 4 hours of ingestion as they are unreliable.

  • But patients may give inaccurate histories
  • If in doubt, treat with NAC.

Risk Assessment

At risk patients requiring hospital based medical assessment

  • Ingested paracetamol in the context of self-harm (irrespective of reported dose) OR
  • Symptomatic OR
  • Ingested 75 mg/kg or more paracetamol over a period of one hour or less OR
  • Time of ingestion is uncertain but the dose ingested is 75 mg/kg or more

Treatment Summary

Timing of Ingestion Acute Overdose: < 8 Hours Acute Overdose: 8-24 Hours Acute Overdose: > 24 Hours Staggered Overdose
Definition All doses ingested during a 1-hour period AND within 8 hrs of presentation All doses ingested during a 1-hour period AND between 8 to 24 hrs of presentation All doses ingested during a 1-hour period AND > 24 hrs before presentation Multiple doses ingested over a period exceeding 1 hour
Gastric Decontamination Consider activated charcoal if within 1 hour of ingestion of ≥150mg/kg (benefit uncertain) Not advised
Timing of Paracetamol Level Blood Test Wait until at least 4 hours post-ingestion Take urgently on arrival Wait until at least 4 hours after the last paracetamol ingestion
Immediate NAC (before paracetamol level)

Start immediate NAC if:

  • Ingested ≥ 150 mg/kg AND
  • Paracetamol level result will be delayed beyond 8h of ingestion

Start immediate NAC if:

  • Ingested ≥ 150 mg/kg OR
  • Ingested unknown amount OR
  • Symptomatic (jaundice or hepatic tenderness)
 Start NAC without delay in ALL patients
Decision to Treat / Risk Assessment

Start/continue NAC if:

  • Above treatment line on nomogram OR
  • Elevated ALT

Start/continue NAC if:

  • Above treatment line on nomogram OR
  • Elevated ALT OR
  • INR > 1.3

Do not use nomogram

Start/continue NAC if:

  • Paracetamol detectable OR
  • Elevated ALT OR
  • INR > 1.3

Do not use nomogram

Stop NAC only if:

  • Paracetamol < 10 mg/L AND
  • Normal ALT AND
  • INR ≤ 1.3 AND
  • No symptoms of liver damage
Medical Discharge Criteria
  • Paracetamol level below treatment line AND
  • Normal INR/ALT AND
  • No symptoms
  • Paracetamol level undetectable AND
  • Normal INR/ALT AND
  • No symptoms
  • Paracetamol < 10 mg/L AND
  • Normal INR/ALT AND
  • No symptoms

Staggered overdose (ingestion over >1hr)

  • Toxicity may occur if >150 mg/kg ingested in any 24-hour period
  • "Initial" Paracetamol levels are unhelpful so treat as OD
  • Treat with NAC (as below) and admit to the CDU

Treatment nomogram

NAC Dosing per SNAP (Scottish & Newcastle Acetylcysteine Protocol)

Patients may give inaccurate histories. If in doubt, treat with NAC.

Please note different concentrations for adults <40kg.

  • Bag 1: 100 mg/Kg in 200 ml (NS or DW5) over 2 Hours
  • Bag 2: 200 mg/Kg in 1000 ml (NS or DW5) over 10 Hours
  • Check bloods (LFTs, INR, U&E, P&S, FBC) 2 hrs before bag 2 infusion due to end

Can discontinue after the 2nd bag if:

  • INR ≤ 1.3 and
  • ALT is normal and
  • Paracetamol conc. < 10 mg/L and
  • Patient has no symptoms suggesting liver damage

If all of these criteria are not met:

  • Continue infusion with a 3rd bag of NAC at the same dose and rate as the 2nd. i.e. 200mg/kg over 10 hours
  • Repeat bloods again after a further 10 hours of treatment

Stop treatment after 3rd bag (22 hours after commencing NAC) if:

  • INR ≤ 1.3 and
  • ALT < x2 upper limit of normal and
  • ALT < x2 the admission measurement

If all of these criteria are not met:

  • Continue infusion at same dose and rate
  • Discuss with NPIS
  • Discuss with Liver unit if not already involved

Specialist advice on those with liver disease.

Discuss (with liver unit) if any of below:

  • ALT > 1000 u/L
  • INR >3.0
  • ↑ creatinine
  • Acidosis or encephalopathy
  • ↓BP (MAP < 60 mmHg)
  • Pre-existing liver disease

Adverse reactions to NAC

  • NAC adverse effects may be localised to infusion site or be more generalised
  • Usually occur during the first 30 minutes of administration (large dose given rapidly)
  • Include nausea, flushing, itching, erythematous rashes, urticaria, angioedema, bronchospasm and, rarely, ↑BP or ↓BP
  • Infusion of NAC should be temporarily stopped and an antihistamine given (± slabutamol neb. if wheeze)
  • Once adverse effects settled, resume infusion at 200mg/kg over 10 hrs

Extravasation

The first infusion has a high osmolarity and may cause venous irritation and tissue damage in cases of extravasation. Administer via a large peripheral vein monitoring insertion site closely using a recognised phlebitis scoring tool. Re-site cannula at first signs of inflammation.

Content by Miriam Flynn (Senior Pharmacist CUH), Dr Finn Coulter, Dr Karol O'Donovan. Last review Dr Amy Brennan 02/10/2026.