Since 2012 the UK uses one treatment line for everyone (100 mg/L at 4 h). Treat without waiting for a level in staggered overdose, uncertain timing, or presentation more than 8 h after a significant ingestion.
Higher-risk liver injury
- The nomogram line is the same for all; these raise clinical concern
- Chronic alcohol excess, malnutrition, eating disorder
- Enzyme-inducing drugs (carbamazepine, rifampicin, phenytoin)
- Late presentation or staggered ingestion
Initial tests
- Paracetamol level at 4 h post ingestion (or on arrival if later)
- A level is only interpretable on the nomogram for a single ingestion at a known time, 4 to 15 h
- ALT, INR, creatinine, venous bicarbonate
- Venous gas, lactate and glucose if unwell
Below line, single timed
- 4 to 15 h level below the 100 line
- Asymptomatic, normal bloods
- Medically fit, psychiatric assessment
Above line / treat empirically
- Above the 100 mg/L at 4 h line
- Staggered or unknown timing
- Start IV NAC now
Hepatotoxicity / King's
- Rising ALT or INR, acidosis
- pH under 7.3 after resuscitation
- Refer to a liver or transplant centre
Management
1
1. Decide on treatment
Within 1 h of a large ingestion, consider activated charcoal. Plot a timed single-ingestion level on the single treatment line (100 mg/L at 4 h). If staggered or timing unknown, treat empirically.
Within 1 h of a large ingestion, consider activated charcoal. Plot a timed single-ingestion level on the single treatment line (100 mg/L at 4 h). If staggered or timing unknown, treat empirically.
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2
2. N-acetylcysteine
IV NAC (21-hour three-bag, or the two-bag SNAP regimen where used) per Toxbase. Start immediately if above the line, late, or staggered.
IV NAC (21-hour three-bag, or the two-bag SNAP regimen where used) per Toxbase. Start immediately if above the line, late, or staggered.
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3
3. Monitor
At the end of NAC, recheck ALT, INR, creatinine and venous bicarbonate. Continue NAC if ALT is rising, INR is above 1.3, or the paracetamol level is still detectable.
At the end of NAC, recheck ALT, INR, creatinine and venous bicarbonate. Continue NAC if ALT is rising, INR is above 1.3, or the paracetamol level is still detectable.
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4
4. Escalate and other ingestions
Refer to a liver or transplant centre if King's criteria are met. Manage co-ingested opioids or salicylates on their own pathways. Mental health assessment before discharge.
Refer to a liver or transplant centre if King's criteria are met. Manage co-ingested opioids or salicylates on their own pathways. Mental health assessment before discharge.
| Trigger | Threshold |
|---|---|
| Arterial pH after resuscitation | Below 7.3 |
| Or all three together | INR over 6.5, creatinine over 300, grade 3 to 4 encephalopathy |
NAC adverse effects
- Anaphylactoid flush or wheeze: slow or pause the infusion, give an antihistamine, then restart
- Do not stop NAC for a reaction if paracetamol is still toxic
Pitfalls
- Using the old 150 or 200 line (all patients now on the 100 line)
- Plotting a level from a staggered or unknown-time ingestion
- Stopping NAC too early with a rising ALT or INR
- Missing co-ingestants
MedPrep - www.medprep.uk - Educational revision aid only. Not clinical guidance. Doses are adult examples; check the BNF, current guidelines and local policy, and seek senior advice. Nov 2026