Acetaminophen metabolites on presentation following an acute acetaminophen overdose (ATOM-7).

Acetaminophen is commonly taken in overdose and can cause acute liver injury via the toxic metabolite NAPQI formed by cytochrome (CYP) P450 pathway. We aimed to evaluate the concentrations of acetaminophen metabolites on presentation following an acute acetaminophen poisoning and whether these predicted the subsequent onset of hepatotoxicity (peak ALT >1000 U/L). The Australian Toxicology Monitoring (ATOM) study is a prospective observational study, recruiting via two PICs and four toxicology units. Patients following an acute acetaminophen ingestion presenting <24h post-ingestion were recruited. Initial samples were analysed for acetaminophen metabolites those measured were the nontoxic glucuronide (APAP-Glu) and sulfate (APAP-Sul) conjugates and NAPQI (toxic metabolite) conjugates APAP-cysteine (APAP-Cys) and APAP-mercapturate (APAP-Mer). The primary outcome was hepatotoxicity. In this study, 200 patients were included, with a median ingested dose of 20g, 191 received acetylcysteine at median time of 5.8h post-ingestion. 26 developed hepatotoxicity, one had hepatotoxicity on arrival (excluded from analysis). Those who developed hepatotoxicity had significantly higher total CYP metabolite concentrations: [36.8μmol/L(IQR: 27.8-51.7) vs 10.8μmol/L(IQR:6.9-19.5)] and these were a greater proportion of total metabolites [5.4%(IQR:3.8-7.7) vs 1.7%(IQR:1.3-2.6)(p<0.001)]. Furthermore, those who developed hepatotoxicity had lower APAP-Sul concentrations [49.1μmol/L(IQR:24.7-72.2) vs 78.7μmol/L (53.6-116.4)] and lower percentage of APAP-Sul [6.3%(IQR:4.6-10.9) vs 13.1%(9.1-20.8)(p<0.001)]. This study found that those who developed hepatotoxicity had higher acetaminophen metabolites derived from CYP pathway and lower sulfation metabolite on presentation. Acetaminophen metabolites may be utilised in the future to identify patients who could benefit from increased acetylcysteine or newer adjunct or research therapies.