Toxicology

Question 1

What is the mechanism of toxicity of paracetamol?

Answer 1

• Three liver metabolic pathways (sulfate, glucuronide, P450)
  
  • P450 pathway creates a toxic free radical intermediate (NAPQI) that is neutralised by GSH
• In high doses, the benign excretion pathways get saturated and NAPQI is produced in levels that cause hepatocyte damage

Question 2

How might you decide how to treat someone who has taken a paracetamol overdose?

Answer 2

• Blood levels (only taken after 4 hours as peak levels before this are difficult to interpret) of paracetamol are plotted on a nomogram and n-acetyl cysteine infusion given according to this
• If after 8 hours post-ingestion, start NaC regardless (liver damage begins here, so one can’t wait for bloods to return)

Question 3

What might someone present with if they’ve been exposed to organophosphates?

Answer 3

• Anticholinergic toxidrome
  
  • Anti-SLUD
  • Dilated pupils (mydriasis) and blurred vision
  • Lack of sweating
  • Tachycardia
  • Confusion
  • Dry mouth
  • Urinary retention