Identification and metabolism of suvorexant: Implications for forensic toxicology

Suvorexant (Belsomra®), a novel dual orexin receptor antagonist for the treatment of insomnia, was recently introduced to the pharmaceutical market in 2015. Insomnia affects up to one-third of the American population, which could make suvorexant a popular option for treating these patients. However, due to its recent introduction to the market, few methods have been developed for the detection of suvorexant and limited case reports have been published that examine suvorexant in forensic toxicology casework. Since a limited number of studies exist detailing the analysis of suvorexant, little is known regarding its role in human performance toxicology and postmortem investigations. This study aimed to further the understanding related to its analytical detection, the identification of metabolites, and the drug’s physicochemical properties. In broader terms, the potential for drug-mediated interferences using liquid chromatography-mass spectrometry (LC-MS) is also addressed. Methods for the detection of suvorexant in blood at forensically relevant concentrations were developed and validated using liquid chromatography-quadrupole/time-of-flight-mass spectrometry (LC-Q/TOF-MS) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Ion suppression and matrix effects using electrospray (ESI) techniques were evaluated and strategies for mitigating interferences in quantitative targeted assays were assessed. The importance of using stable isotope labeled internal standards (SIL-IS) was highlighted using a statistical comparative approach with a structurally similar analog. Suvorexant was quantitated in forensic case specimens and its lipophilicity was determined experimentally and theoretically to evaluate its potential to undergo postmortem redistribution (PMR). In the absence of commercially available metabolite standards, major metabolites for suvorexant were produced in vitro using recombinant cytochrome P450 enzyme systems and were subsequently identified in authentic case specimens.