48 Calpol: are we overdosing on blood tests?

Background

In February 2012, the Commission on Human Medicines recommended lowering the paracetamol toxicity treatment threshold for all patients. Children between one month and six years of age are physiologically distinct and metabolise paracetamol differently, making them less prone to toxicity. Furthermore, overdose in early childhood is almost exclusively accidental, as opposed to predominately deliberate self harm seen in adults and adolescents. As a result, the use of the new 75 mg/kg ingestion threshold for young children would appear to be of unproven benefit, and is substantially lower than the threshold used in other countries.

Aim

To establish the sensitivity and negative predictive value of using a 150 mg/kg ingestion threshold to identify hepatotoxicity in children one month to six year old group with paracetamol overdoses.

Method

Retrospective case review. Potential cases were identified by filtering an electronic Patient Management System for a discharge diagnosis of 'accidental ingestions and poisonings' over the period 1 st January 2012 to 19th October 2016 (57 months). ED documentation was reviewed to identify cases of paracetamol ingestions by children under the age of 6 years. Those with intentional harm, known staggered ingestions over 1 hour or under one month age (corrected for gestation) were excluded.

Clinical notes and laboratory data were reviewed and, data parameters collated using a standardised proforma. Ingested doses were estimated, where possible, by subtraction methods. In some cases, the ingestion time was revised according to the time that the child was previously seen prior to the ingestion. A composite outcome for hepatotoxicity was used consisting firstly of the current UK standard treatment threshold (100 mg/L line on paracetamol toxicity nomogram) together with any evidence of biochemical hepatoxicity or clinical features of potential hepatotoxicity at any subsequent ED attendances over the next 7 days.

Results

The final cohort consisted of 165 individual patient ingestions. A 150 mg/kg ingestion threshold had a sensitivity of 100.0% (95% CI:47.5 to 100.0) for hepatotoxicity, with a negative predictive value of 100% (95% CI:97.5 to 100.0).

Conclusion

This retrospective study supports the hypothesis that accidental paracetamol ingestions less than 150 mg/kg, in children one month to six years of age, can be safely managed without investigation or treatment, in accordance with other international guidance. The use of 150 mg/kg threshold would reduce testing in over a third of attendances in our cohort. Study limitations include retrospective bias and the predominate use of serum paracetamol levels to determine toxicity.

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