Abstract

Lemborexant is a novel dual orexin receptor antagonist recently approved for the treatment of insomnia in the United States and Japan. Here, disposition and metabolic profiles were investigated in healthy human subjects. After single oral administration of 10 mg [¹⁴C]lemborexant (100 µCi), plasma concentrations of lemborexant and radioactivity peaked at 1 hour postdose and decreased biphasically. Cumulative recovery of the administered radioactivity within 480 hours was 86.5% of the dose, with 29.1% in urine and 57.4% in feces. Unchanged lemborexant was not detected in urine but accounted for 13.0% of the dose in feces, suggesting that the main elimination pathway of lemborexant was metabolism. Metabolite analyses revealed that the major metabolic pathways of lemborexant are oxidation of the dimethylpyrimidine moiety and subsequent further oxidation and/or glucuronidation. In plasma, lemborexant was the dominant component, accounting for 26.5% of total drug-related exposure. M4, M9, M10, and M18 were detected as the major radioactive components; M10 was the only metabolite exceeding 10% of total drug-related exposure. Although M4, M9, and M10 showed binding affinity for orexin receptors comparable to that of lemborexant, their contributions to the sleep-promoting effects of lemborexant are likely low because of the limited brain penetration by P-glycoprotein. Exposure comparison between humans and nonclinical toxicology species confirmed that plasma exposure of M10 was higher in at least one animal species compared with that in humans, indicating that there is no disproportionate metabolite in humans, as defined by International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use M3(R2) and U.S. Food and Drug Administration Metabolite in Safety Testing guidance; therefore, no additional toxicology studies are needed.