title: Effects of cytochrome P450 2D6 and 3A5 genotypes and possible coadministered medicines on the metabolic clearance of antidepressant mirtazapine in Japanese patients.
abstract: A personalized treatment approach should be considered with the second-generation psychiatric drug mirtazapine because of high frequencies of side effects, including characteristic drowsiness. Plasma concentrations of mirtazapine in patients are influenced by many factors, including polymorphic cytochrome P450 enzymes contributing to its transformation to 8-hydroxymirtazapine and N-demethylmirtazapine. The aim of this study was to investigate the determinant factors for individual variations of metabolic clearance of mirtazapine using in vitro and in vivo methods. In vitro analyses using liver microsomes from individual humans in correlation assays and recombinantly expressed P450 enzymes revealed that CYP2D6 was the major contributor to mirtazapine 8-hydroxylation with high affinity, and that CYP3A5 catalyzed N-demethylation in a similar high-capacity manner to that of CYP3A4. CYP1A2 was a minor contributor to mirtazapine 8-hydroxylation. Metabolic clearance of mirtazapine determined in substrate depletion assays and mirtazapine 8-hydroxylation activities in individual liver microsomes were significantly lower in CYP2D6 intermediate metabolizers (IM) and poor metabolizers (PM) than in extensive metabolizers (EM) (p<0.05). Trough plasma concentration/dose ratios of mirtazapine from 14 patients were significantly higher in the CYP2D6 IM/PM group than in the EM group and were also higher in the CYP3A5 poor-expressors group than in the expressors group (p<0.05). Mirtazapine clearance in pooled human liver microsomes was inhibited by quinidine (a CYP2D6 inhibitor), ketoconazole (a CYP3A inhibitor), and in combination with risperidone and duloxetine, possible coadministered medicines. These results suggested that mirtazapine metabolic clearance could be variously influenced by the CYP2D6 and CYP3A5 genotypes and coadministered drugs in clinical patients.
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan.
authors.forename: Maho
authors.initials: M
authors.lastname: Okubo
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan.
authors.forename: Norie
authors.initials: N
authors.lastname: Murayama
authors.affiliation: Muroran Institute of Technology, Muroran 050-8585, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Miura
authors.affiliation: Sanai Hospital, Noboribetsu 059-0463, Japan.
authors.forename: Yasuji
authors.initials: Y
authors.lastname: Chiba
authors.affiliation: Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Machida, Tokyo 194-8543, Japan. Electronic address: hyamazak@ac.shoyaku.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamazaki
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000928:Antidepressive Agents / Q000008:administration & dosage*; D044466:Asian People / Q000235:genetics*; D019389:Cytochrome P-450 CYP2D6 / Q000235:genetics* / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A / Q000235:genetics* / Q000378:metabolism; D004359:Drug Therapy, Combination; D005260:Female; D005838:Genotype; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate / Q000187:drug effects / Q000502:physiology; D008803:Mianserin / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism; D008875:Middle Aged; D000078785:Mirtazapine
chemical_list: D000928:Antidepressive Agents; D008803:Mianserin; D000078785:Mirtazapine; C510164:CYP3A5 protein, human; D019389:Cytochrome P-450 CYP2D6; D051544:Cytochrome P-450 CYP3A
keywords: CY3A5; CYP2D6; Genetic polymorphisms; Mirtazapine; Plasma concentration