Determination of Common Metabolites for Methoxylated Fentanyl Analogs

Background/Objectives: The opioid crisis is an ongoing problem in the United States, and fentanyl analogs play a major role in the issue, as novel fentanyl analogs are constantly being developed. Substitutions and additions to the fentanyl scaffold impact the potency of the substances and can sometimes influence the biotransformation of the drugs. This study aimed to determine whether one or more common metabolites could be detected among a group of five methoxylated fentanyl analogs, for the purpose of eventually providing a more rapid detection method for new and unknown fentanyl-related compounds in toxicological samples. Methods: In vitro metabolism via pooled human liver microsomes (HLMs) was performed for five methoxylated fentanyl analogs (para-methoxyfentanyl, ortho- and para-methoxy butyryl fentanyl, and ortho- and para-methoxy furanyl fentanyl) to generate metabolites. Assays were analyzed via liquid chromatography–tandem mass spectrometry. Results: Nine metabolites were detected. A common metabolite was observed between fentanyl analogs that were methoxylated at the para-position. Conclusions: Similarities between metabolites of five methoxylated fentanyl analogs were noted. It appeared that the major pathway of metabolism for methoxylated fentanyl analogs is largely consistent, regardless of the location of the methoxy substituent so long as the piperidine nitrogen is unobstructed and is available for N-dealkylation. This research provides valuable insight to potentially find new ways for toxicologists to identify novel methoxylated fentanyl analogs in biological matrices.