Mark McCullagh
Managing Paracetamol Overdose: Lessons from reported incidents
In this article, Mark McCullagh, pharmacist and Clinical Risk Advisor, reviews incidents related to the treatment of paracetamol overdose reported on NIMS, the National Incident Management System, and provides risk mitigation advice to enhance patient safety.
Managing Paracetamol Overdose: Lessons from reported incidents
Paracetamol is a widely used analgesic which is available without prescription in Ireland. It is generally considered safe at therapeutic doses and is suitable for use in children and in pregnant women. Compared to other non-prescription analgesics, paracetamol has a relatively narrow therapeutic index. The toxic dose of paracetamol is 10 times the therapeutic dose whereas the toxic dose of ibuprofen is 60 times the therapeutic dose.1
Paracetamol overdose and treatment
Paracetamol overdose (OD) causes dose-dependent hepatotoxicity which can lead to liver failure. As little as 10g (20 x 500mg tablets) of paracetamol can cause severe hepatotoxicity in an adult.1 Approximately 12-13% of acute paracetamol ODs result in hepatotoxicity even with treatment, with 2-5% progressing to liver failure.1
Paracetamol is the most common drug OD in the UK, accounting for over 100,000 presentations to emergency departments and resulting in 100-150 deaths annually.2 N-acetylcysteine (NAC) prevents paracetamol-induced hepatotoxicity, particularly when administered within eight hours of paracetamol ingestion, and is a highly effective antidote. Before the availability of NAC, mortality following paracetamol OD was 3-5%, but has fallen to less than 1% since its introduction.1
The licensed NAC treatment regimen for paracetamol OD is complex, consisting of three infusions over 21 hours, each of which has a different dose, rate of infusion and duration of administration.3 This complexity may cause treatment delays resulting in avoidable hepatotoxicity.4
N-acetylcysteine incident data
The Clinical Risk Unit undertook a review of five years of NAC incidents logged on NIMS, the National Incident Management System. The search identified 66 relevant incidents which were analysed for common themes (table 1).
Incident Theme | Number of Incidents |
Administration incident | 40 |
Prescribing incident | 16 |
Adverse drug reaction | 8 |
Preparation/dispensing incident | 1 |
Other | 1 |
Total | 66 |
Table 1. NAC incidents by theme
Incidents under a common theme were further grouped into subthemes
1. Administration incidents
Administration incidents accounted for 61% of NAC incidents, by theme, in the treatment of paracetamol OD. The most common administration incident subthemes were delay in treatment, incorrect rate of administration and reconstitution error.
"Patient prescribed N-acetylcysteine (administered as three consecutive infusions). Staff did not notice that infusion one had finished. Delay in commencement of infusion two."
Example of an incident on NIMS
2. Prescribing incidents
Prescribing incidents accounted for 24% of NAC incidents, by theme, in the treatment of paracetamol OD. The most common prescribing incident subthemes were incorrect dose and prescription incomplete.
"N-acetylcysteine protocol prescribed for paracetamol overdose. The third infusion was prescribed incorrectly i.e. NAC 10,000mg prescribed but correct dose is 100mg/kg. Clinical pharmacist informed team. Correct dose subsequently administered."
Example of an incident on NIMS
3. Adverse drug reactions and other incidents
The remaining 15% of NAC incidents in the treatment of paracetamol OD included adverse drug reactions to NAC and other incidents.
Advice to reduce the risk of incidents in the treatment of paracetamol OD
- Paracetamol OD requires urgent medical attention to determine if the patient is at risk of hepatotoxicity and to allow for the timely administration of NAC where indicated.
- For advice on prescribing or administering NAC for paracetamol OD, refer to local guidelines or consult a recognised reference source such as the Summary of Product Characteristics3 or the British National Formulary.5
- Administration in accordance with licensed / locally approved NAC regimens requires forward planning to ensure there are no delays between infusions.
- For expert advice on treatment of poisoning, including paracetamol OD, contact the National Poisons Information Centre of Ireland.
References available on request
Clinical Risk Insights
Clinical Risk Insights is the regular newsletter issued by the Clinical Risk Unit of the State Claims Agency for health and social care workers in Ireland.
