Reported ingested dose of paracetamol as a predictor of risk following paracetamol overdose

To evaluate reported ingested dose of paracetamol as a risk assessment tool in acute paracetamol overdose.

Data was retrospectively obtained from a clinical toxicology database linked to one Australian and two United Kingdom hospitals. Plasma paracetamol concentrations (PPCs) of adult patients presenting with acute single ingestion, non-staggered paracetamol deliberate self-poisoning between 2006 and 2012 were recorded and plotted on a treatment nomogram to determine accuracy of reported dose ingested as an indicator for antidotal treatment. PPC plotted on a treatment nomogram with a line intersecting a 4-h concentration of 100 mg/L [667 μmol/L] was considered an indication for antidotal treatment in the UK; the corresponding Australasian population utilised a line intersecting 150 mg/L [1000 μmol/L].

Of 1246 patients, 65.7 % were female and 88 % were from the UK. Fifty-two percent of patients reporting ingestion of ≥8 g paracetamol had a PPC above the 100 mg/L treatment line; PPV 52 % [95 % confidence interval (CI) 49 %, 55 %], sensitivity 81 % [95 %CI 78 %, 85 %]. Forty-four of patients reporting percent ingestion of ≥10 g had a PPC above the 150 mg/L treatment line; PPV 44 % [95 % CI 41 %, 49 %], sensitivity 85 % [95 % CI 78 %, 89 %], 72 % of patients reporting ingestion of ≥16 g had a PPC above the 100 mg/L treatment line; PPV 72 % [95% CI 67 %, 77 %], sensitivity 50 % [95 % CI 45 %, 54 %]. Overall, there was moderate correlation (R = 0.58) between reported paracetamol dose ingested and extrapolated 4-h PPC.

There is a positive correlation between reported ingested dose of paracetamol and subsequent chance of a PPC being above a defined treatment line; however, ingested dose of paracetamol alone is a poor risk assessment tool in accurately determining need for treatment with an antidote.