title: Inhibitory effects of the monoamine oxidase inhibitor tranylcypromine on the cytochrome P450 enzymes CYP2C19, CYP2C9, and CYP2D6.
abstract: 1. The inhibitory effects of tranylcypromine, a nonselective irreversible inhibitor of monoamine oxidase (MAO), on three cytochrome P450 (CYP) enzymes, namely CYP2C9, CYP2C19, and CYP2D6, have been evaluated in vitro. 2. The studies were conducted using cDNA-expressed human CYP enzymes and probe substrates. 3. A range of substrate concentrations was coincubated with a range of tranylcypromine concentrations in the presence of each of the CYP enzymes at 37 degrees C for a predetermined period of time. Product concentrations were quantified by HPLC with UV detection. 4. The results demonstrated that tranylcypromine is a competitive inhibitor of CYP2C19 (Ki = 32 microM) and CYP2D6 (Ki = 367 microM) and a noncompetitive inhibitor of CYP2C9 (Ki = 56 microM). 5. None of these inhibitory effects are considered clinically significant at usual therapeutic doses. However, in certain situations such as high dose tranylcypromine therapy, or in poor metabolizers of CYP2C19 substrates, clinically significant interactions might occur, particularly when tranylcypromine is coadministered with drugs with a narrow therapeutic index.
authors.affiliation: Neurochemical Research Unit, Department of Psychiatry, Mackenzie Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2R7. salsali@ualberta.ca
authors.forename: Mahnaz
authors.initials: M
authors.lastname: Salsali
authors.forename: Andrew
authors.initials: A
authors.lastname: Holt
authors.forename: Glen B
authors.initials: GB
authors.lastname: Baker
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D065731:Cytochrome P-450 CYP2C19; D065729:Cytochrome P-450 CYP2C9; D019389:Cytochrome P-450 CYP2D6 / Q000378:metabolism; D065690:Cytochrome P-450 CYP2D6 Inhibitors; D003915:Dextromethorphan / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions / Q000502:physiology; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology; D008617:Mephenytoin / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology*; D014044:Tolbutamide / Q000494:pharmacology; D014191:Tranylcypromine / Q000494:pharmacology*
chemical_list: D065690:Cytochrome P-450 CYP2D6 Inhibitors; D008996:Monoamine Oxidase Inhibitors; D014191:Tranylcypromine; D003915:Dextromethorphan; D014044:Tolbutamide; D006899:Mixed Function Oxygenases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19; D019389:Cytochrome P-450 CYP2D6; D008617:Mephenytoin