If a patient vomits after taking paracetamol (acetaminophen), can another full dose be administered?

Management of Paracetamol (Acetaminophen) After Vomiting

If a patient vomits after taking paracetamol, another full dose can be administered if vomiting occurred within 30 minutes of ingestion, as absorption would likely be incomplete.

Factors to Consider When Deciding to Readminister Paracetamol

• The timing of vomiting after ingestion is the most critical factor in determining whether to administer another dose 1:

  • If vomiting occurs within 30 minutes of ingestion, absorption is likely incomplete and another full dose can be given
  • If vomiting occurs after 30 minutes, significant absorption may have already occurred, and readministration risks exceeding safe dosage limits

• The maximum safe daily dose of paracetamol must be considered to prevent hepatotoxicity 2:

  • Adults should not exceed 4000 mg (4 g) in 24 hours
  • No more than 6 doses should be taken in 24 hours

Risk Assessment for Paracetamol Toxicity

• Repeated supratherapeutic ingestions (RSTI) of paracetamol can lead to hepatotoxicity, hepatic failure, and even death 3

• Potentially toxic doses include 1:

  • Single ingestions exceeding 10 grams or 150 mg/kg in adults
  • Repeated ingestions totaling ≥10 grams or 200 mg/kg over a 24-hour period
  • Repeated ingestions of ≥6 grams or 150 mg/kg per 24-hour period for 48 hours or longer

• For high-risk individuals (those with chronic alcohol consumption, pre-existing liver disease), the threshold for toxicity is lower at >4 grams or 100 mg/kg per day 1

Algorithm for Managing Paracetamol After Vomiting

1. Assess timing of vomiting:

   • If vomiting occurred within 30 minutes of ingestion → Administer another full dose 4
   • If vomiting occurred after 30 minutes → Do not administer another full dose; consider a partial dose based on time elapsed

2. Calculate total daily dose including the readministered dose:

   • Ensure total daily dose remains below 4000 mg (4 g) for adults 2
   • For high-risk individuals, ensure total daily dose remains below 3000 mg (3 g) 1

3. If vomiting persists:

   • Consider alternative routes of administration (rectal suppository) 4, 5
   • Consider alternative analgesics if appropriate

Special Considerations

• Patients with chronic liver disease should use paracetamol with caution, though it remains the non-opiate analgesic of choice in elderly persons and patients with chronic renal insufficiency 4

• Paracetamol absorption is affected by:

  • Gastric emptying rate (delayed by food)
  • Formulation (effervescent tablets are absorbed more rapidly than conventional tablets) 4

• If vomiting continues after readministration, this may indicate a more serious condition requiring medical evaluation 2

Warning Signs of Potential Toxicity

• Monitor for signs of hepatotoxicity if there is concern about excessive dosing 1, 2:

  • Nausea and vomiting
  • Right upper quadrant pain
  • Elevated liver enzymes
  • Jaundice

• Seek immediate medical attention if signs of overdose develop, as early intervention with N-acetylcysteine can prevent severe liver damage 6