Treatment of Paracetamol Overdose

In overdose the potential risk of a patient having significant liver damage is directly proportional to the amount of paracetamol ingested. Acetylcysteine IV (N-acetylcysteine, Parvolex^®, NAC) is the treatment of choice. It has near 100% efficacy in preventing paracetamol-induced hepatotoxicity if given within the first 8 hours from ingestion of overdose. It may also be effective up to and possibly beyond 24 hours.

This guideline reflects the local NHSAAA policy on acetylcysteine use in adult paracetamol overdoses and is based on the Scottish and Newcastle Anti-emetic Pre-treatment for Paracetamol Poisoning (SNAP) regime. The same dose of N-acetylcysteine is administered in this regime but over a 12-hour (not 21-hour) treatment period. While the MHRA has not yet approved its use, TOXBASE lists the regime as a recognised treatment period. 

The chart below should be used when there has been determined a need to treat a paracetamol excess with acetylcysteine. To determine the need for acetylcysteine please consult TOXBASE (password required). The NHSAAA IV Acetylcysteine Prescribing and Administration Chart is located in all Emergency Departments and Medical Receiving areas. 

• NHSAAA IV Acetylcysteine Prescribing and Administration Chart

Special groups

• Low weight - patients <40kg, use the paediatric regime on TOXBASE (password required) for management as this protocol is not applicable.
• High weight - patients >110kg can be treated using this protocol. For this group a weight of 110kg should be used to calculate their toxic dose (mg/kg) and their acetylcysteine dose.
• Pregnancy - patients who are pregnant can be treated using this protocol. Their toxic dose (mg/kg) should be calculated using their pre-pregnancy weight. The drug dose should be calculated using their actual pregnancy weight.
• Paediatric - consider discussion with a paediatrician for patients under 13 years old but >40kg.
• Patients for whom IV acetylcysteine treatment is not possible - see TOXBASE (password required) guidance on oral administration of acetylcysteine (off-label) or seek advice from NPIS (0344 892 0111).

N.B. TOXBASE (password required) should continue to be used as a clinical decision support resource in conjunction with the National Poisons Information Service (NPIS, 0344 892 0111).