|Hours post dose||UK/Australia||USA||Risk factors|
The 3 columns reflect the 3 most commonly used nomogram lines. Although the lines are commonly extrapolated to 24 hours, they have not been validated beyond 16 hours.
Column one reflects Prescott's original data and is widely used in the United Kingdom, Australia and Europe.
Column two reflects the original USA study protocol and is the standard of care in USA.
Column three is not based on any good data, see high risk groups (below).
Either of the UK or USA columns is reasonable to assess risk and need for therapy for most patients, the US line is more aggressive.
Paracetamol (acetaminophen) concentrations are commonly reported in either SI units (micromol/L or mmol/L) or in mass units (mg/L). This can sometimes lead to confusion when interpreting results to assess the risk of hepatotoxicity. Be sure that you know which units your laboratory uses.
Theoretically toxicity is more likely if the P450 enzymes are induced by chronic alcohol ingestion, anticonvulsants or barbiturates (i.e. more toxic metabolite). Inhibition of P450 enzymes at the time of the overdose may reduce the production of toxic metabolites. This most commonly occurs with acute alcohol ingestion (4-6 drinks) & may also occur with co-ingestions or chronic medication with drugs that inhibit these enzymes (e.g. cimetidine). Patients with depleted glutathione may be at increased risk of toxicity e.g. chronic ingestion of paracetamol, malnutrition & eating disorders.
The nomogram represented by the risk column has been suggested to be used for these patients.