title: Quantification of the steady-state plasma concentrations of clozapine and N-desmethylclozapine in Japanese patients with schizophrenia using a novel HPLC method and the effects of CYPs and ABC transporters polymorphisms.
abstract: Background This study developed a novel high-performance liquid chromatography (HPLC) method for the simultaneous quantification of clozapine and its active metabolite, N-desmethylclozapine, in human plasma and investigated the effects of various factors, including genetic polymorphisms in cytochrome P450 (CYP) 2D6, CYP3A5, ABCB1 and ABCG2, on the steady-state plasma trough concentrations (C0) of clozapine and N-desmethylclozapine in Japanese patients with schizophrenia. Methods Forty-five patients had been receiving fixed doses of clozapine for at least four weeks. The CYP2D6 ( CYP2D6*2, CYP2D6*5, CYP2D6*10), CYP3A5 ( CYP3A5*3), ABCB1 (1236C > T, 2677G > T/A, 3435C > T) and ABCG2 (421 C > A) genotypes were identified by polymerase chain reaction. Results The within- and between-day coefficients of variation (CV) were less than 11.0%, and accuracy was within 9.0% over the linear range from 10 to 2500 ng/mL for both analytes, and their LOQs were each 10 ng/mL. The median C0/dose (C0/D) ratios of clozapine were significantly higher in patients with the ABCG2 421 A allele than in those with the 421 C/C genotype ( P = 0.010). However, there were no significant differences in C0/D ratios of clozapine and N-desmethylclozapine among ABCB1, CYP2D6 or CYP3A5 genotypes. In multiple regression analysis, including polymorphisms, age, body weight and biochemical data of patients, the ABCG2 polymorphism alone was correlated with the C0/D ratios of clozapine ( R2= 0.139, P = 0.016). Conclusions Among the various CYPs and drug transporters, BCRP appeared to most strongly influence clozapine exposure. Knowledge of the patient's ABCG2 421 C > A genotype before initiating therapy may be useful when making dosing decisions aimed at achieving optimal clozapine exposure.
authors.affiliation: 1 Department of Pharmacy, Akita University Hospital, Akita, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Akamine
authors.affiliation: 2 Department of Neuropsychiatry, Akita University Graduate School of Medicine, Akita, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Sugawara-Kikuchi
authors.affiliation: 3 Department of Pharmacy, Zikeikai-Aoimori Hospital, Aomori, Japan.
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Uno
authors.affiliation: 2 Department of Neuropsychiatry, Akita University Graduate School of Medicine, Akita, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Shimizu
authors.affiliation: 1 Department of Pharmacy, Akita University Hospital, Akita, Japan.
authors.forename: Masatomo
authors.initials: M
authors.lastname: Miura
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D000368:Aged; D001774:Blood Chemical Analysis / Q000379:methods*; D002851:Chromatography, High Pressure Liquid; D003024:Clozapine / Q000031:analogs & derivatives* / Q000097:blood* / Q000493:pharmacokinetics; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D005260:Female; D005838:Genotype; D006801:Humans; D007564:Japan; D008297:Male; D008875:Middle Aged; D011110:Polymorphism, Genetic; D012559:Schizophrenia / Q000097:blood* / Q000235:genetics / Q000378:metabolism; D055815:Young Adult
chemical_list: D018528:ATP-Binding Cassette Transporters; C058272:norclozapine; D003577:Cytochrome P-450 Enzyme System; D003024:Clozapine
keywords: ABCG2 polymorphism; Clozapine; N-desmethylclozapine; drug-transporters; therapeutic drug monitoring