Question 12

A 50-year-old female with a history of depression and osteoarthritis has presented to hospital with a suspected ingestion of 50 tablets of Panadol Osteo® (modified release paracetamol 665 mg/tablet). It is believed there was suicidal intent and roughly occurred five hours prior. She remains asymptomatic, is remorseful of her actions, and quite anxious.

Her vital parameters are stable; and paracetamol level is plotted in the nomogram below (Figure 12.1):

paracetamol nomogram

a)    Outline the initial specific investigations and management.    (30% marks)

b)    Explain the role and rationale of N-acetylcysteine (NAC) (based on nomogram) in this patient.
(30% marks)

c)    List the criteria for cessation in patients who require NAC beyond 20 hours.    (20% marks)

d)    List the criteria for consultation with liver transplant unit in patients with paracetamol toxicity.
(20% marks)

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College answer

Not available.


The original college nomogram is not available, so this one is entirely the invention of the author. 

Anyway: this is a relatively large overdose, 33.25g. Assuming this lady weighs 70kg, that would be 475mg/kg, an overdose which would be described as "massive" by local definitions

a) Initial specific investigations and management:

  • Investigations:
    • EUC/CMP, looking for renal failure
    • LFTs, looking for hepatic enzyme elevation
    • Coags, looking for coagulopathy
    • ABG, looking for acidosis
    • BSL, looking for hypoglycaemia
  • Management:
    • Usually, one would say that this would be too late for activated charcoal (as it is only useful within 4 hours of ingestion), but considering the overdose was large and the patient appears to be cooperative, 50g of activated charcoal should be administered
    • N-acetylcysteine infusion should start (high dose, 200mg/kg over first 4 hours, followed by 200mg/kg over 16 hours).

Role and rationale of N-acetylcysteine (NAC) (based on nomogram) in this patient

  • The nomogram cannot be used to guide therapy in this patient, as she has overdosed on a sustained-release formulation.
  • NAC infusion will continue for the full 20 hours, minimum - irrespective of the initial level
  • Paracetamol levels are still useful to guide further NAC dosing (beyond the initial 24 hrs) and the need for more charcoal decontamination
  • If the levels continue to rise in the first 24 hrs, or remain over 100mg/L, the dose of NAC may need to increase.
    Which brings us to:

The criteria for cessation in patients who require NAC beyond 20 hours:

  • Continue NAC if:
    • Paracetamol concentration remains more than 10 mg/L (66 µmol/L) 
    • ALT is > 50 U/L and increasing
    • INR is more than 2.0
    • Patient is clinically unwell

Criteria for referral to a liver transplant unit:

  • INR more than 3.0 at 48 hours or greater than 4.5 at any time;
  • Oliguria or creatinine greater than 200 μmol/L
  • Persistent acidosis (pH <  7.3) or arterial lactate greater than 3 mmol/L
  • Hypotension with blood pressure below 80  mmHg
  • Hypoglycaemia, severe thrombocytopenia, or encephalopathy of any degree
  • Any unexplained alteration of consciousness (Glasgow Coma Score <  15)


Chiew, Angela L., et al. "Updated guidelines for the management of paracetamol poisoning in Australia and New Zealand." Medical journal of Australia 212.4 (2020): 175-183.

The actual guideline document itself is marvellously comprehensive and contains everything you could possibly want for this SAQ: