Therapeutics- Paracetemol Flashcards
What is the toxic metabolite of paracetamol?
NAPQI
How is NAPQI normally detoxified?
Glutathione conjugation at the liver
What organs are damaged in paracetamol overdose?
Liver and kidney
Kidney failure can occur in isolation of liver failure
What is a staggered dose?
Paracetamol overdose taken over more than an hour
How much time must be given to take a blood paracetamol concentration?
4 hours after the OD as this is when absorption is complete
What is given in parcetemol overdose? What is it?
Acetylcysteine is given IV over 21 hours
It is a glutathione precursor (this detoxifies NAPQI)
What reaction might be seen to acetylcysteine? Should the infusion be stopped?
Anaphylactoid reactions may be seen in around 10-15% of cases, this is not a contra-indication but anti-histamines may be required
What is the 8 hour rule?
Acetylcysteine should be given within 8 hours to reduce the risk of hepatotoxicity
No benefit is gained from giving it before 8 hours and so it is worth waiting for the results of a blood parcetemol concentration within this window
What should be done with late presenters?
Give acetylcysteine
There is an increased risk of hepatotoxicity with later delivery of the antidote
What should be done for a staggered overdose?
Give acetylcysteine regardless
What is the 24 hour rule?
24 hours after a parcetemol overdose any patient who is asymptomatic, has normal ALT and INR and no parcetemol in the plasma is safe to be discharged
What might back pain be a sign of with parcetemol overdose?
Renal toxicity/failure
What biochemical abnormalities may be seen with parcetemol overdose?
ALT/ AST- very raised Bilirubin- raised INR- raised Clotting factors- low Metabolic acidosis- renal failure causes reduced hydrogen ion excretion Blood sugar- low Phosphate- low
What are some prognostic factors in late presenters?
PT/INR (raised) Creatinine (raised) pH (Acidosis) Presence of encephalopathy Age
