In silico, in vitro and in vivo metabolite identification of brexpiprazole using ultra‐high‐performance liquid chromatography/quadrupole time‐of‐flight mass spectrometry

Rationale Brexpiprazole is a novel serotonin–dopamine activity modulator approved by the USFDA in July 2015 for the treatment of schizophrenia and as an adjunctive therapy with other antidepressants for major depressive disorder in adults. However, limited numbers of metabolites are reported in the literature for brexpiprazole. Our prime intent behind this study is to revisit metabolite profiling of brexpiprazole and to identify and characterize all possible in vitro and in vivo metabolites. Methods Firstly, the site of metabolism for brexpiprazole was predicted by a Xenosite web predictor model. Secondly, in vitro metabolite profiling was performed by incubating the drug individually with rat liver microsomes, human liver microsomes and rat S9 fraction at 37°C for 1 h in incubator shaker. Finally, for in vivo metabolite identification, a 50 mg kg −1 dose of brexpiprazole was administered to male Sprague–Dawley rats and the presence of various metabolites was confirmed in rat plasma, urine and feces. Results The predicted atomic site of metabolism was obtained as a color gradient by the Xenosite web predictor tool and, from this study, probable metabolites were listed. In total, 14 phase I and 2 phase II metabolites were identified and characterized in the in vitro and in vivo matrices using ultra‐high‐performance liquid chromatography/quadrupole time‐of‐flight tandem mass spectrometry (UHPLC/QTOF‐MS/MS). The majority of metabolites were found in the sample incubated with human liver microsomes and in rat urine, while in the other matrices only a few metabolites were detected. Conclusions All the 16 metabolites were identified and characterized using UHPLC/QTOF‐MS/MS. The study revealed that brexpiprazole is metabolized via hydroxylation, glucuronidation, S‐oxidation, N‐oxidation, dioxidation, oxidative deamination, N‐dealkylation, etc.