Paracetamol Overdose

Exam Cram

• Paracetamol is broken down into NAPQI, toxic to liver

• Glutathione naturally neutralises NAPQI, in overdose it becomes overwhelmed

• Paracetamol OD results in acute hepatitis

• Management: NAC (exogenous glutathione) to neutralise NAPQI

OUtline

Background

Paracetamol is a common drug of choice in overdose and a common cause of acute hepatitis, in particular requiring an emergency liver transplant.

Assessment

History

• Overdose: tablets- when, what and how many

• Elimination: any vomiting, diarrhoea

• Previous liver disease

Examination

• Tender abdomen, particularly RUQ

• Hypovolaemic hypotension and tachycardia

Investigations

• Paracetamol level- measure 4hrs post ingestion

• LFTs- ALT/ AST

• Coag- INR

• VBG: pH ?acidosis

Management

• NAC

• IVF

• Consider Toxicology or Liver transplant consults

• Analgesia (of course not paracetamol!) and antiemetics

Med Reg Notes

Initial Management

Starting NAC

1. If less than 200mg / kg or 10g in 24hrs then no treatment required

2. If paracetamol ingestion > 8hrs, start NAC and take full set of bloods

3. If paracetamol ingestion < 8hrs and level can be done before 8hrs, wait till paracetamol level has come back before starting NAC

4. If paracetamol ingestion < 4hrs, take level after 4hrs

5. If staggered overdose, start NAC

Plot paracetamol level on nomogram

1. If above line, continue NAC

2. If below line and ALT/ INR normal stop NAC

Indications to stop NAC (varies by trust)

• Once paracetamol levels, INR and ALT have normalised

• E.g. paracetamol < 10, INR < 1.5 and ALT < 50

Inpatient Management

Require repeat paracetamol level, INR and ALT results prior to NAC bag finishing (e.g. 2hrs before finish)

Prognosis

NAC is considered to be 100% effective when given within 8hrs. 

Predicting Liver Failure

• INR > 2.0 after 48hrs or > 3.5 after 72hrs, poor prognosis

• SBP < 80

Monitor requirement for liver transplant- King's College Criteria:

• pH < 7.3

• INR > 6.5

• Creatinine > 300

• Grade III or IV encephalopathy

Discharge planning

Medically discharged usually once NAC finished

Requires Psychiatry suicide risk assessment by Mental Health team once NAC finished ?admit psych / discharge with outpatient follow up

NAC Side Effects

Anaphylactoid

Hypersensitivity reaction

Infusion related side effects

• Related to speed of infusion

• Presentation: facial flushing, itching, hypotension

• Management: 

  • Stop infusion & A-E assessment

  • Antihistamines, 

  • Restart infusion at a slower rate (if symptoms have resolved)

References

1. https://litfl.com/paracetamol-toxicity/

Page written in 2024.