Paracetamol (acetaminophen) hepatotoxicity increases in the presence of an added herbal compound.

Hepatotoxicity from paracetamol/acetaminophen has occasionally been reported at lower than expected doses. As herbal preparations may interact with pharmaceutical drugs the following in vitro study was undertaken to determine whether the toxic effects of paracetamol on liver cell growth in culture would be exacerbated by the addition of psoralen, a furanocoumarin compound that is present in Psoralea corylifolia, a common Chinese herb. The following study utilising a liver carcinoma cell line (HepG2) showed that Psoralea corylifolia was significantly toxic from 0.3 mg/ml to 5 mg/ml (p < 0.05), whereas paracetamol was not toxic below 50 mM (p = 0.0026). Interactions between previously non-toxic levels of 0.1 mg/ml of Psoralea corylifolia and increasing concentrations of paracetamol (0-50 mM), however, were observed, with a significant increase in toxicity compared to paracetamol alone (30% cell death vs. 72% cell death with Psoralea corylifolia). A significant synergistic interaction was observed at 40 mM paracetamol with 0.1 mg/ml of Psoralea (p = 0.038). This study has, therefore, shown significantly increased hepatotoxicity in cell cultures exposed to paracetamol when herbal compounds containing furanocoumarins were added. Fulminant acute liver failure occurring after the ingestion of low doses of paracetamol may not, therefore, always be due to an occult idiosyncratic response to paracetamol, but instead possibly to the combined effects of paracetamol and herbal preparations. Given the widespread use of both paracetamol and herbal preparations this possibility should be considered in cases of unexplained hepatic necrosis and liver failure that present for medicolegal investigation.