Paracetamol poisoning Flashcards
Name 3 risk factors for paracetamol hepatotoxicity?
Alcohol
Malnutrition
Staggered overdose
Pre-existing liver disease
What is the antidote for paracetamol overdose?
N-acetylcysteine
What is the pathophysiology of paracetamol poisoning?
- Paracetamol normally converted to harmless metabolite (glucurodination and sulfation), but instead is converted to NAPQI
- Glutathione is required to inactivate NAPQI
- Insufficient glutathione reserve because of overdose means that NAPQI accumulates
- NAPQI causes oxidative stress and hepatocellular damage
What is the mechanism of action for N-acetylcysteine?
Replenishes glutathione reserves
What bloods to do in paracetamol overdose?
Paracetamol levels --> normogram INR U + E VBG (for lactate) FBC LFT
Give 4 indications for acetylcysteine administration
1) Plasma paracetamol levels are on or above treatment levels
2) Staggered overdose
3) Patient seen within 8 hours of consuming 150mg/kg paracetamol but normogram results take more than 8 hours to come back
4) Patient seen 8 - 24hours after paracetamol ingestion with dose of 150mg/kg
5) Evidence of acute liver injury regardless of when paracetamol was ingested
What is the infusion protocol for acetylcysteine?
21 hours infusion - 3 consecutive infusions (1h, 4h, 16h)
The dosage for each infusion is:
- 150mg/kg (add acetylcysteine concentrate 200mg/ml volume to 200mL NaCl 0.9% according to weight)
- 50mg/kg (as above, add to 500mL NaCl 0.9%)
- 100mg/kg (as above, add to 1000mL NaCl 0.9%)
You patient suddenly gets a rash after taking acetylcysteine, what has happened?
- Anaphylactoid reaction (happens in 15% of patients)
- Stop the infusion
- Give H1 antihistamine i.e chlorphenamine 10mg IV
- restart infusion at slower rate
-Follow anaphylaxis algorithm if evidence of cardiorespiratory compromise
When does the effectiveness of N-acetylcysteine begin to wane?
Between 10 and 24 hours post-overdose
