title: A high-throughput assay using liquid chromatography-tandem mass spectrometry for simultaneous in vivo phenotyping of 5 major cytochrome p450 enzymes in patients.
abstract: The phenotyping cocktail is a practical approach for phenotyping of cytochrome P450 (CYP) enzymes in vivo. In this study, a liquid chromatography-tandem mass spectrometry method using a dual-extraction approach was developed and validated to quantify 5 selective substrates and their metabolites for the simultaneous phenotyping CYPs 1A2, 2C19, 2C9, 2D6, and 3A4 in patient blood samples. The assay was applied in a pilot study of 11 patients with schizophrenia. Five blood samples were collected before and at 1, 2, 4, and 6 hours after administration of a phenotyping cocktail consisting of 100 mg caffeine, 20 mg omeprazole, 25 mg losartan, 30 mg dextromethorphan, and 2 mg midazolam. The method successfully quantitated the CYP enzyme activities without serious side effects in patients. The ratios of metabolite to parent area under the concentration-time curve values were calculated over the 6-hour postdosage to reflect CYP2D6, CYP3A4, and CYP2C9 activities. The ratios of metabolite to parent plasma concentrations were calculated at 4-hour postdosage for CYP1A2 and at 4- or 6-hour postdose for CYP2C19, respectively. The plasma concentration of midazolam at 4 hours was also estimated as another phenotyping index for CYP3A4 activity. The simultaneous assay of all these analytes in a single matrix (plasma) will increase the feasibility of CYP phenotyping in patients.
authors.affiliation: Faculty of Pharmacy, University of Sydney, Camperdown, New South Wales, Australia.
authors.forename: Sussan
authors.initials: S
authors.lastname: Ghassabian
authors.forename: Manoranjenni
authors.initials: M
authors.lastname: Chetty
authors.forename: Bruce N
authors.initials: BN
authors.lastname: Tattam
authors.forename: Mraci C
authors.initials: MC
authors.lastname: Chem
authors.forename: John
authors.initials: J
authors.lastname: Glen
authors.forename: Jeannie
authors.initials: J
authors.lastname: Rahme
authors.forename: Zvijezdana
authors.initials: Z
authors.lastname: Stankovic
authors.forename: Iqbal
authors.initials: I
authors.lastname: Ramzan
authors.forename: Michael
authors.initials: M
authors.lastname: Murray
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: McLachlan
mesh_terms: D001711:Biotransformation; D002110:Caffeine / Q000493:pharmacokinetics; D002853:Chromatography, Liquid; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D003915:Dextromethorphan / Q000493:pharmacokinetics; D006801:Humans; D019808:Losartan / Q000493:pharmacokinetics; D008874:Midazolam / Q000493:pharmacokinetics; D009853:Omeprazole / Q000493:pharmacokinetics; D010641:Phenotype; D053719:Tandem Mass Spectrometry
chemical_list: D002110:Caffeine; D003915:Dextromethorphan; D003577:Cytochrome P-450 Enzyme System; D019808:Losartan; D009853:Omeprazole; D008874:Midazolam