Paracetamol Overdose

Question 1

What is the mechanism of injury in paracetamol overdose?

Answer 1

• Hepatic cytochrom P450 enzyme metabolises paracetamol
• This forms alkylating metabolite known as NAPQI (N-acetyl-p-benzoquinone
• NAPQI should be irreversibly conjugated with sulhydryl groups of glutathione
• Intermediate product NAPQI is hepatotoxic
• In overdose NAPQI not cleared = adverse effect and death

Question 2

What is the presentation of paracetamol overdose?

Answer 2

• Frequently asymptomatic
• Nausea & vomiting (usually settle in 24hrs)
• Right subcostal pain + prolonged N&V =hepatic necrosis
• Coma /reduced consciousness
• Tachypnoea due to metabolic acidosis
• Hypoglycaemia

Question 3

What are the signs of hepatic injury in paracetamol overdose?

Answer 3

• Nausea and vomiting in 24hrs
• Subcostal pain
• Jaundice

Question 4

What are the signs of encephalopathy in paracetamol injury?

Answer 4

• Confusion

* Disorientation

Question 5

What are the adverse effects of paracetamol on the body?

Answer 5

*Hepatic necrosis can lead to:
>Encephalopathy
>Hypoglycaemia
>Haemorrhage
>Cerebral oedema
>Death

Question 6

What investigations should be done in paracetamol overdose?

Answer 6

1. Paracetamol level
   >taken 4hours post ingestion
   >immediately if patient arrive 4hours after taken or if taken a staggered overdose
2. Bloods
3. ECG

Question 7

What specific questions should be asked in a patient who has taken a paracetamol overdose?

Answer 7

1. When they took the tablets?
2. Was it staggered or all at once?
3. How many they have taken?

Question 8

What makes a patient above the treatment threshold?

Answer 8

1. If there is a staggered overdose or doubt over time of paracetamol ingestion regardless of paracetamol concentration or
2. plasma paracetamol above treatment line on normagram i.e. 100mg/L at 4 hours

Question 9

What is on a paracetamol overdose normogram chart?

Answer 9

• Plasma paracetamol concentration
• Time in hours since taking overdose
• Treatment threshold line

Question 10

What are the management steps of treating a paracetamol overdose?

Answer 10

1. A-E assessment
2. TOXBASE consultation if situation out of normal

3a. Treat with Acetylcysteine if:
>staggered overdose
>unsure on time
>above treatment threshold

3b. Can treat with activated charcoal if within 1hour of overdose

Question 11

What are the correct treatment doses of acetylcystein for a paracetamol ovedose?

Answer 11

3 doses:

1st: 150mg/kg over 1 hour
2nd: 50mg/kg over 4hours
3rd: 100mg/kg over 16hours

Question 12

What is counted as a staggered overdose?

Answer 12

If tablets are not taken within same 1 hour period

Question 13

How does acetylcystein work?

Answer 13

Increases concentration of glutathione available for conjugation of NAPQI