SAQ 69 – Toxicology – paracetamol overdose nomogram and NAC

Question 2. paracetamol overdose nomogram and NAC.

a. Nomogram criteria. (5 marks)

• Time of ingestion is known.
• Presentation is 4 to 24 hours after ingestion.
• Single acute ingestion.
• Standard-release paracetamol preparation.
• Patient is older than 16 years.

b. Toxic dose threshold. (1 mark)

• More than 200 mg/kg or more than 10 g, whichever is lower.

c. Biochemical hepatic injury definition. (1 mark)

• ALT or AST greater than 1000.

d. Staggered standard-release ingestion. (4 marks)

• Use the earliest ingestion time as the anchor, treating it as the worst-case timing.
• Measure a paracetamol concentration.
• If below the nomogram treatment line, no further investigation or treatment is required.
• If above the treatment line, complete a 20-hour NAC course.
• Activated charcoal is not indicated.

e. Slow-release ingestion at 3 hours. (6 marks)

• Give activated charcoal if the patient is awake and cooperative.
• Start NAC.
• Measure paracetamol concentrations at 4 and 8 hours.
• If both levels are below the treatment line and falling, no further treatment is required.
• If either level is above the treatment line, complete 20 hours of NAC.
• If NAC continues, repeat ALT and paracetamol at 18 hours; continue NAC if ALT is greater than 50 or paracetamol is greater than 66 umol/L.

f. Massive standard-release ingestion at 4 hours. (5 marks)

• Measure paracetamol concentration immediately.
• If below the nomogram treatment line, no further treatment is required.
• If above the treatment line, complete double-dose NAC for 20 hours.
• At 18 hours, repeat ALT and paracetamol; continue NAC if ALT is greater than 50 or paracetamol is greater than 66 umol/L.
• Consult a toxicologist.