Poisoning approach and drug overdoses

Paracetamol poisoning

Reviewed Nov 2026·3 references
New· views rounded down, updated weekly

Risk-assess with the nomogram, give acetylcysteine by the two-bag regimen, extend for massive ingestion, and know when to refer for transplant.

Definition
Toxicity is possible after ≥ 200 mg/kg or ≥ 10 g (whichever is less) in 24 h. For single acute ingestion with known time (4-24 h), plot the level on the nomogram (ANZ/US treatment line 150 mg/L at 4 h; UK uses 100 mg/L).

At the bedside

  1. 1

    Activated charcoal

    Within 2 h of ingestion ≥ 10 g/200 mg/kg (within 4 h for massive ingestion ≥ 30 g or ≥ 500 mg/kg).

  2. 2

    Level at ≥ 4 h

    Plot on nomogram; treat if above line. Unknown time, staggered ingestion, or presentation > 8 h after a toxic dose: start NAC immediately and check level and ALT.

  3. 3

    Acetylcysteine

    Two-bag: 200 mg/kg over 4 h, then 100 mg/kg over 16 h. Do not wait for levels if > 8 h after ingestion.

  4. 4

    Massive ingestion

    Level > 2 × nomogram line (> 300 mg/L at 4 h) or ≥ 30 g: double the second bag (200 mg/kg over 16 h); consider haemodialysis if level very high with coma and lactic acidosis.

  5. 5

    End of infusion

    Check paracetamol and ALT: stop if paracetamol < 10-20 mg/L and ALT normal/falling; otherwise continue 100 mg/kg/16 h and repeat.

  6. 6

    Liver failure

    INR rising, encephalopathy, acidosis: continue NAC, refer to liver unit, apply King's College criteria (see liver failure module).

Paracetamol poisoning (two-bag)

N-acetylcysteine

IV
Dose
200 mg/kg over 4 h, then 100 mg/kg over 16 h
Preparation
Bag 1 in 500 mL 5% dextrose; bag 2 in 1,000 mL
Worked example
70 kg: 14 g in 500 mL over 4 h (125 mL/h), then 7 g in 1,000 mL over 16 h (62.5 mL/h)

Early presentation

Activated charcoal

Oral
Dose
50 g

Paracetamol risk assessment

ScenarioAction
Single acute, 4-24 h, known timeLevel; NAC if above 150 mg/L line at 4 h (nomogram)
Presentation < 4 hCharcoal if < 2 h; level at 4 h
> 8 h after ≥ 200 mg/kg / 10 gStart NAC now; level + ALT
Staggered or unknown timeNAC if ≥ 200 mg/kg or 10 g in 24 h, or level > 20 mg/L, or ALT raised
Massive (≥ 30 g or level ≥ 2× line)Charcoal up to 4 h; double second NAC bag; toxicology advice
Red flag · call your senior now
Early coma and lactic acidosis with a very high level (> 700-800 mg/L): mitochondrial toxicity - consider haemodialysis with NAC.
Pitfall
Using the nomogram for staggered or modified-release ingestions.
Pitfall
Stopping NAC at a fixed time despite rising ALT or detectable paracetamol.
Pearl
NAC is almost completely protective if started within 8 h of ingestion.

Calculators for this topic

Infusion rate from a fixed hourly or per-minute dose

Pump rate for non-weight-based infusions such as vasopressin (U/min), labetalol (mg/min) or amiodarone (mg/h).

References

  1. 1

    Chiew AL, Reith D, Pomerleau A, et al. Updated guidelines for the management of paracetamol poisoning in Australia and New Zealand. Med J Aust 2020;212:175-83.

  2. 2

    Dart RC, Mullins ME, Matoushek T, et al. Management of acetaminophen poisoning in the US and Canada: a consensus statement. JAMA Netw Open 2023;6:e2327739.

  3. 3

    Bateman DN, Dear JW, Thanacoody HKR, et al. Reduction of adverse effects from intravenous acetylcysteine treatment for paracetamol poisoning (SNAP): a randomised controlled trial. Lancet 2014;383:697-704.

Test yourself

Module quiz · score 70% to complete the module

Previous

Decontamination and enhanced elimination

Next

Cardiotoxic overdoses: TCA, beta-blockers, CCB, digoxin

Educational reference for trained clinicians. Check doses against your hospital protocol and the patient in front of you.