Paracetamol poisoning Flashcards
What is the therapeutic dose for paracetamol?
4g over 24 hours
What is paracetamol broken down into and how can this cause damage?
Broken down by the liver to sulphate, glucuronide and a small amount is converted to NAPQI. NAPQI is toxic and is conjugated by glutathione to non-toxic metabolites that are excreted
How does paracetamol overdose damage the liver and kidneys?
It damages the liver through glutathione depletion and the NAPQI also has direct oxidating effects.
Renal injury is caused by endoperoxide synthase enzymes.
What are the four main things that influence hepatotoxicity of paracetamol?
The dose of paracetamol
Plasma concentration
Time to antidote administration
Whether the overdose was taken staggered or all at once
What are the different doses and liklihood of liver damage?
<75mg/kg - Extremely unlikely
75-100mg/kg - Rare
>150mg/kg - Possible
how long after ingestion of paracetamol will plasma concentrations be accurate?
4 hours
What is the antidote given for paracetamol overdose?
Glutatione preursors, the most common is acetlycystiene
How is acetylcystiene given?
As three bags of fluid each with a slightly decreased dose
What is a major adverse effect that can be seen with acetylcycstiene?
Anaphylactoid features
When must the antidote be administered?
Within 8 hours of the overdose, always worth waiting for 4 hours for plasma levels to make sure someone is not being unessesarily treated.
This should not be done if this means treatment will be after 8 hours or if the person says they have had over 75mg/kg
What is the definition of a staggered overdose?
Total amount spread over more than 60 minutes
What biochemical abnormalities are seen in paracetamol overdose?
Raised serum paracetamol
Raised ALT and AST
Decreased blood glucose
Metabolic acidosis
What are some of the clinical features of paracetamol overdose?
Day 1 asymptomatic/ nausea and vomiting
Day 2 nausea, hepatic tenderness, mild jaundice
Day 3 jaundice, liver failure, encephalopathy, cardiac arrest
