Clinical Practice Guidelines

Paracetamol Poisoning

  • See also: General Management of Acute Poisoning Guideline

    Patients Requiring Management

    • Acute ingestion of > 200 mg/kg
    • Ingestion of unknown quantity
    • Repeated supratherapeutic ingestion of > 100mg/kg/day


    Consider the possibility of co ingestions, either accidental or deliberate


    • Activated charcoal is not useful in liquid ingestions due to rapid absorption
    • Activated charcoal 1 g/kg may be considered in a cooperative patient seen within 1 hour of tablet or capsule ingestion.
    • Serum paracetamol level at (or as soon as possible after) 4 hours post ingestion determines the need for N-acetyl cysteine (NAC) administration.  (see nomogram)
    • There is no benefit in measuring paracetamol level earlier than 4 hours
    • It is safe to wait for the paracetamol level to decide on the need for NAC in all cases that present within 8 hours of ingestion.
    • Patients who present > 8 hours after a toxic ingestion / symptoms of toxicity (RUQ pain or tenderness, nausea, vomiting) should be commenced on NAC immediately.  The decision to continue or cease NAC is then based on the paracetamol level.  Delaying NAC administration beyond 8 hours is associated with a progressive increased risk of liver injury.
    • There is little evidence to guide management in repeated supratherapeutic doses.  Potential toxicity should be assessed when:
      • > 200 mg/kg (or 10g) ingested over a 24 hour period
      • > 150 mg/kg/day (or 6 g) ingested over a 48 hour period
      • > 100 mg/kg/day ingested over a 72 hour period
    • See management algorithm and NAC infusion guide.

    Paracetamol ingestion flowchart






    Nomogram For Paracetamol Poisoning

    N-Acetyl cysteine (NAC) Infusion Instructions

    The standard administration of NAC is a 3 stage infusion giving a total dose of 300 mg/kg:

    1. 150 mg/kg over the first hour
    2. 50 mg/kg over the next 4 hours
    3. 100mg/kg over the next 16 hours

    For patients > 110 kg, calculate the dose based on 110 kg body weight.

    NAC may be diluted in 5% dextrose or 0.9% saline (normal saline).  It can also be diluted in combination dextrose-saline solutions not exceeding these concentrations including 0.45% saline in 5% dextrose, and 0.9% saline in 5% dextrose.

    The volume and choice of fluid for each stage of the infusion needs to be appropriate for the age and weight of the child and clinical circumstances.  In the adolescent patient, it is generally appropriate to follow the standard published recommendations for NAC administration and use convenient volumes for administration:

    For adolescent / adult:

    1. 150 mg/kg in 250 or 500 ml over 1 hour
    2. 50 mg/kg in 500 ml over 4 hours
    3. 100 mg/kg in 1000 ml over 16 hours

    However, this results in a total of 1700 mls of 5% dextrose which is inappropriate for smaller children. 

    For smaller children a suggested approach is:

    NAC Dose

    Dilute in (saline or dextrose)

    Duration (Rate)

    150 mg/kg

    250 ml bag

    1 hour (250 ml/hr)

    50 mg/kg

    250 ml bag

    4 hours (65 ml/hr)


    250 ml bag

    16 hours (15 ml/hr)

    For infants , even smaller volumes may be required.  Doses can be diluted in 100 ml bags if available or added to an appropriate volume in a burette. 

    In all cases, additional maintenance fluids can be given if required, or NAC may be administered in larger volume bags if more convenient.


    Anaphylactoid reactions to NAC may occur (wheeze, rash).  In these cases, cease the infusion for 30 minutes, give promethazine then recommence the infusion at half the previous rate.  Slowly increase the rate until the desired rate is again reached.

    Evidence suggests those treated with NAC within 8 hours of ingestion can cease the infusion after 21 hours without the need for LFT monitoring or further investigation.  In those presenting with delayed toxic ingestions or after multiple supratherapeutic dose toxicity, LFT monitoring can be used to determine the duration of NAC therapy.  If ALT is elevated at the completion of the 21 hour infusion, NAC should be continued at the current rate and specialist advice sought.