Acetaminophen (Paracetamol) Poisoning: Mnemonic Approach

Rule of 150 and 4

a. Begin treatment if: Paracetamol is ingested at a dose >150 mg/kg

Threshold to begin treatment is half the dose (75 mg/kg) in high risk cases:

1. Regular ethanol consumption: >21 Units/week in male and >14 Units/week in female

2. Regular use of enzyme inducing drugs: carbamazepine, phenytoin, phenobarbitone, rifampicin

3. Conditions causing glutathion depletion: malnutrition, HIV, eating disorder, cystic fibrosis

Remember the 3 E – Ethanol, Enzyme inducer, Eating disorder

b. Within 4 hours of ingestion: Oral/NG/OG Activated Charcol (1/50, i.e. 1 gm/kg or 50 gm)

c. Send Serum APAP level after 4 hours post-ingestion and Start NAC if: Serum APAP level >150 microgram/ml at 4 hours post-ingestion (or use Rumack-Matthew normogram for acute ingestion upto 24 hours) OR Ingested dose >150 mg/kg and Serum APAP level cannot be obtained within 8 hours post-ingestion or patient presents after 8 hours or if the dosing is staggered

rumack matthew normogram
Merlin Cyrstal [CC BY-SA 3.0], via Wikimedia Commons

d. NAC dosing:

  1. Loading: 150 mg/kg IV in 200 ml (3 ml/kg) 5%DW over 1 hour
  2. Maintenance: 150 mg/kg IV in (21 ml/kg) 1500 ml 5%DW over 20 hours.
    • 1/3rd in 1st 4 hours
    • 2/3rd in later 16 hours

Oral dose of NAC:
1. Loading: 140 mg/kg
2. Maintenance: 70 mg/kg every 4 hours for 17 doses

Rechecking serum APAP level:
1. IV NAC dosing: at 20 hours
2. Oral NAC dosing: at 24 hours

NAC can be started empirically if serum APAP level is not obtained within 8 hours and it can be stopped prior to completion of total regimen if:
a. APAP level returns to 0
b. INR <2
c. AST normalizes

King’s college Criteria

It is used for predicting fulminant hepatic failure and referral to the transplant center.

Mnemonic: A or B, C and D

a. Acidosis: Arterial pH <7.3 or lactate >3 OR

b. All of the following:

  1. Bleeding risk: PT >100s or INR >6.5
  2. Creatinine: >3.4 mg/dl
  3. Drowsiness: Hepatic Encephalopathy Grade III or IV


  1. Wallace CI, Dargan PI, Jones ALParacetamol overdose: an evidence based flowchart to guide managementEmergency Medicine Journal 2002;19:202-205.
  2. The Washington Manual of Medical Therapeutics – By Hemant Godara

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