Division of Clinical Pharmacology

Paracetamol toxicity may occur due to deliberate over-ingestion with intent of self-harm or accidental overdose due to exceeding safe intake when self-medicating. The aim of this study is to identify patients in this second group where usual history-taking has not identified the paracetamol overdose. For information on acute paracetamol overdose see Paracetamol.

Study Protocol

All samples sent to pathology from the ED with a serum ALT >50 U/L will have a serum paracetamol assay performed on the sample unless the test has been performed previously. The results will be placed in Mediweb along with the other patient results.

Interpretation

The therapeutic interval for serum paracetamol is 10 - 20 mg/L. As the time of maximum ingestion may be longer ago than the standard dosing interval, even a "therapeutic" concentration may reflect potentially dangerous ingestion and the usual paracetamol toxicity nomogram may not apply. All results >10 mg/L should be further investigated.

Actions

In response to a serum paracetamol greater than 10 ug/L the following actions should be undertaken rapidly.

1. Take a repeat history of paracetamol ingestion. Note that many over-the counter products contain paracetamol. History should include specific questioning for pain medication, cold and flu or sinus medication. Be especially aware of co-adminsitration of paracetamol-containing products (eg panadeine together with panamax) The dosage and timing of paracetamol intake should be assessed as carefully as possible. A list of medications containing paracetamol is displayed below.
2. Assessment of patient risk factors for toxicity. A patient is at higher risk of paracetamol toxicity if they are: pregnant; chronic alcoholics; on microsomal inducing drugs (eg barbiturates, carbamazepine, rifampicin, isoniazid, omeprazole, oral contraceptives, HIV medication); likely to have glutathionie depletion (prolonged poor nutrition, anorexia); underlying liver disease.
3. Discussion of case with ED consultant or registrar for consideration of N-acetyl cysteine (Parvolex) treatment.

Medications containing paracetamol

Below is an incomplete list of medications available in Australia containing paracetamol. For a complete list see MIMs.