In vitro metabolism of the novel synthetic opioid agonist cyclopropylfentanyl and subsequent confirmation in authentic human samples using liquid chromatography-high resolution mass spectrometry.

Novel synthetic opioids (NSOs) are a class of novel psychoactive substances (NPS) that are growing in popularity and presenting a significant public health risk. Included in this class are derivatives of the highly potent analgesic, fentanyl. Cyclopropylfentanyl (CycP-F) was first reported to the EU Early Warning System in August 2017, and was subsequently linked to more than 100 deaths in the US alone. Limited pharmacological, pharmacokinetic or toxicological data is available for many emerging NSOs; however we can expect novel fentanyl analogues to present limited detection windows, short onset, narrow therapeutic indices and the potential for very high potency. Knowledge of the metabolism of these drugs is essential for the identification of analytical targets for their detection. Therefore in vitro metabolites of CycP-F were produced using human liver microsomal incubations. Metabolites formed were elucidated using liquid chromatography-high resolution accurate mass analysis (LC-HRAM). Identified metabolites were added to our accurate mass screening database for NPS which was utilised for subsequent screening analysis. CycP-F and metabolites were identified in two human blood case samples. Eleven metabolites were identified in vitro, with the major metabolites produced via N-dealkylation, monohydroxylation and N-oxidation. Analysis of the positive case samples identified four in vivo metabolites, all of which were observed in vitro. The major metabolite identified in vitro and in vivo was the N-dealkylated nor-metabolite; two further mono-hydroxylated and one dihydroxylated metabolite were detected in vivo.