Search

A sensitive and selective method using high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC–ESI–MS) to determine the concentration of torasemide in human plasma samples was developed and validated. Tolbutamide was chosen as the internal standard (IS). The chromatography was performed on a Gl Sciences Inertsil ODS-3 column (100 mm×2.1 mm i.d., 5.0 µm) within 5 min, using methanol with 10 mM ammonium formate (60:40, v/v) as mobile phase at a flow rate of 0.2 mL/min. The targeted compound was detected in negative ionization at m/z 347.00 for torasemide and 269.00 for IS. The linearity range of this method was found to be within the concentration range of 1–2500 ng/mL ( r =0.9984) for torasemide in human plasma. The accuracy of this measurement was between 94.05% and 103.86%. The extracted recovery efficiency was from 84.20% to 86.47% at three concentration levels. This method was also successfully applied in pharmacokinetics and bioequivalence studies in Chinese volunteers. [ABSTRACT FROM AUTHOR]

What is known and objective: Cytochrome P450 2C9 (CYP2C9) is a polymorphic enzyme that is responsible for clearing approximately 15% of clinically important drugs. The objective of this study was to assess the catalytic characteristics of 39 CYP2C9 isoforms found in the Chinese population and their effects on the metabolism of the model substrate fluoxetine in vitro. Methods: Baculovirus-mediated expressing system was used to highly express wild-type and the 38 CYP2C9 allelic variants in insect cell microsomes. Then, the enzymatic characteristics of each variant were evaluated using fluoxetine as the substrate. Reactions were performed at 37 °C with the insect microsomes and 10-200 lM fluoxetine for 60 min. After termination, the products were precipitated and used for signal collection by UPLC-MS/MS. Results and discussion: Of the 39 tested CYP2C9 isoforms, only four variants (CYP2C9*3, CYP2C9*27, CYP2C9*34 and CYP2C9*37) exhibited similar relative clearance values to that of the wild-type CYP2C9*1. Moreover, five variants (CYP2C9*14, CYP2C9*36, CYP2C9*45, CYP2C9*48 and CYP2C9*55) showed a higher intrinsic clearance value than the wild-type protein, whereas the remaining 29 CYP2C9 isoforms exhibited significantly decreased clearance values (from 623% to 8774%) compared to CYP2C9*1. In addition, 28 CYP2C9 isoforms including CYP2C9*3 exhibited a trend towards substrate inhibition for fluoxetine. What is new and conclusion: This study provides the most comprehensive data on the enzymatic activities associated with all reported CYP2C9 variants in the Chinese population with regard to the widely used antidepressant drug, fluoxetine. Our data indicate that more attention should be paid to subjects carrying the corresponding infrequent CYP2C9 alleles when administering fluoxetine in the clinic. [ABSTRACT FROM AUTHOR]

The primary objectives of this study were to investigate the suitability of a 6-probe cocktail (caffeine, tolbutamide, omeprazole, dextromethorphan, midazolam, and digoxin) to be used as a tool for assessing the activity of drug metabolizing enzymes and transporters, and examine differences in the way drugs are handled among groups with different genetic regulation of these processes. This was a single-center, open-label, phase I clinical study involving 20 young, healthy Chinese volunteers (equal gender distribution). The subjects were administered a single, oral dose of the 6-probe cocktail and serum samples were collected to assess the disposition of the different probe substrates and produced metabolites. The serum samples were analyzed using ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry technology. The DNA samples were subjected to whole exome sequencing. Nineteen healthy volunteers completed the study. The 6-probe cocktail was safe and well-tolerated by all the subjects. The parent substrates and metabolites-caffeine (paraxanthine), dextromethorphan (dextrorphan), digoxin, midazolam (1-hydroxy-midazolam), omeprazole (5-hydroxy-omeprazole), and tolbutamide (4-hydroxy-tolbutamide)-were within the detectable window. Genetic variations known to alter drug metabolism (CYP2D6*10, CYP2C19*2, CYP2C19*3, and CYP2C9*3) were identified and generally correlated with phenotypic status. The 6-probe cocktail appeared to be suitable for assessing drug metabolizing activities. This, in conjunction with individual genetics, will pave the way for the implementation of personalized medicine in clinical practice. This will hopefully improve efficacy and reduce the incidence of adverse drug reactions., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)