Incorporation of suvorexant and lemborexant into hair and their distributions after a single intake.

Purpose: This study examined the applicability of hair analysis as an approach to identify suvorexant (SUV) and lemborexant (LEM) intake by analyzing black hair specimens collected from study participants after a single oral administration.

Methods: Hair specimens were collected form participants who took a single dose of 10 mg SUV or 5 mg LEM. Identification of the dual orexin receptor antagonists (DORAs) and their metabolites was performed by liquid chromatography-tandem mass spectrometry. Reference standards of S-M9 and L-M4, the metabolites of SUV and LEM, respectively, were synthesized in our laboratory. Sectional analysis of 1-mm segments of the single-hair strands was also performed to investigate the incorporation behavior of the drugs into hair.

Results: Unchanged SUV and LEM, and their metabolites S-M9 and L-M4 were detected even in the single-hair specimens. Results of the segmental hair analysis showed predominant incorporation of the drugs into hair through the hair bulb region rather than through the upper dermis zone of the hair root. The drug concentrations in the hair specimens, collected about 1 month after intake, were 0.033-0.037 pg/hair strand (0.17-0.19 pg/mg) for SUV and 0.054-0.28 pg/hair strand (0.28-1.5 pg/mg) for LEM. The calculated distribution ratios of the DORAs into hair to the oral doses were much lower than those of benzodiazepines and zolpidem reported in a previous study.

Conclusions: This is the first report of the detection of the DORAs in hair. The incorporation behavior of the DORAs into hair revealed herein are crucial for proper interpretation of hair test results.