Effects of CYP2C9 genetic polymorphisms on the pharmacokinetics of zafirlukast

Physiologically based pharmacokinetic (PBPK) modeling to predict the pharmacokinetics of irbesartan in different CYP2C9 genotypes

Irbesartan, a potent and selective angiotensin II type-1 (AT1) receptor blocker (ARB), is one of the representative medications for the treatment of hypertension. Cytochrome P450 (CYP) 2C9 is primarily involved in the oxidation of irbesartan. CYP2C9 is highly polymorphic, and genetic polymorphism of this enzyme is the leading cause of significant alterations in the pharmacokinetics of irbesartan. This study aimed to establish the physiologically based pharmacokinetic (PBPK) model to predict the pharmacokinetics of irbesartan in different CYP2C9 genotypes. The irbesartan PBPK model was established using the PK-Sim® software. Our previously reported pharmacogenomic data for irbesartan was leveraged in the development of the PBPK model and collected clinical pharmacokinetic data for irbesartan was used for the validation of the model. Physicochemical and ADME properties of irbesartan were obtained from previously reported data, predicted by the modeling software, or optimized to fit the observed plasma concentration-time profiles. Model evaluation was performed by comparing the predicted plasma concentration-time profiles and pharmacokinetic parameters to the observed results. Predicted plasma concentration-time profiles were visually similar to observed profiles. Predicted AUCinf in CYP2C9*1/*3 and CYP2C9*1/*13 genotypes were increased by 1.54- and 1.62-fold compared to CYP2C9*1/*1 genotype, respectively. All fold error values for AUC and Cmax in non-genotyped and CYP2C9 genotyped models were within the two-fold error criterion. We properly established the PBPK model of irbesartan in different CYP2C9 genotypes. It can be used to predict the pharmacokinetics of irbesartan for personalized pharmacotherapy in individuals of various races, ages, and CYP2C9 genotypes.

Effects of paroxetine on the pharmacokinetics of atomoxetine and its metabolites in different CYP2D6 genotypes

The aim of this study was to investigate the  effects of paroxetine, a potent inhibitor of CYP2D6, on the pharmacokinetics of atomoxetine and its two metabolites, 4-hydroxyatomoxetine and N-desmethylatomoxetine, in different CYP2D6 genotypes. Twenty-six healthy subjects were recruited and divided into CYP2D6*wt/*wt (*wt=*1 or *2, n = 10), CYP2D6*wt/*10 (n = 9), and CYP2D6*10/*10 groups (n = 7). In atomoxetine phase, all subjects received a single oral dose of atomoxetine (20 mg). In paroxetine phase, after administration of a single oral dose of paroxetine (20 mg) for six consecutive days, all subjects received a single oral dose of atomoxetine with paroxetine. Plasma concentrations of atomoxetine and its metabolites were determined up to 24 h after dosing. During atomoxetine phase, there were significant differences in C_max and AUC_0-24 of atomoxetine and N-desmethylatomoxetine among three genotype groups, whereas significant differences were not found in relation to CYP2D6*10 allele after administration of paroxetine. AUC ratios of 4-hydroxyatomoxetine and N-desmethylatomoxetine to atomoxetine were significantly different among three genotype groups during atomoxetine phase (all, P < 0.001), but after paroxetine treatment significant differences were not found. After paroxetine treatment, AUC_0-24 of atomoxetine was increased by 2.3-, 1.7-, and 1.3-fold, in CYP2D6*wt/*wt, CYP2D6*wt/*10, and CYP2D6*10/*10 groups in comparison to atomoxetine phase, respectively. AUC ratio of 4-hydroxyatomoxetine to atomoxetine in each group was significantly decreased, whereas AUC ratio of N-desmethylatomoxetine to atomoxetine significantly increased after administration of paroxetine. In conclusion, paroxetine coadministration significantly affected pharmacokinetic parameters of atomoxetine and its two metabolites, 4-hydroxyatomoxetine and N-desmethylatomoxetine. When atomoxetine was administered alone, C_max, AUC_0-24 and CL/F of atomoxetine were significantly different among the three CYP2D6 genotype groups. However, after paroxetine coadministration, no significant differences in these pharmacokinetic parameters were observed among the CYP2D6 genotype groups.

Effects of CYP2D6 genetic polymorphism on the pharmacokinetics of metoclopramide

Metoclopramide inhibits the central and peripheral D₂ receptors and is frequently prescribed in adults and children as an antiemetic or a prokinetic drug to control symptoms of upper gastrointestinal motor disorders. Metoclopramide is predominantly metabolized via N-dealkylation and it is primarily mediated by CYP2D6 which is highly polymorphic. Thus, the effects of CYP2D6 genetic polymorphism on the pharmacokinetics of metoclopramide were evaluated in this study. All volunteers were genotyped for CYP2D6 and divided into four different genotype groups (CYP2D6*wt/*wt [*wt = *1 or *2], CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10). Each subject received a single oral dose of metoclopramide 10 mg. Plasma concentrations of metoclopramide were measured by using HPLC-UV. Compared to CYP2D6*wt/*wt, AUC_inf of CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10 significantly increased by 1.5-, 2.3-, and 2.5-fold, respectively. C_max also increased significantly in comparison to CYP2D6*wt/*wt across all genotype groups, with 1.5-, 1.7-, and 1.7-fold increases seen in CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10 groups, respectively. The CL/F of metoclopramide decreased in CYP2D6 genotype groups with decreased function alleles, as decreases of 37%, 56% and 61% were observed in CYP2D6*wt/10, *10/10, and *5/*10 genotype groups in comparison to the CYP2D6*wt/*wt group. In conclusion, the genetic polymorphisms of CYP2D6 significantly affected metoclopramide pharmacokinetics.

Genetic variations in drug-metabolizing enzyme CYP2C9 among major ethnic groups of Pakistani population

The genetic polymorphism of cytochrome P450 (CYPs)drug-metabolizing enzymes are well studied in human populations for drug safety and efficacy. CYP2C9 is a highly polymorphic CYP enzyme that oxidizing the indigenous compounds and xenobiotics. The present study was pursued to evaluate the genetic variation across the CYP2C9 gene among major groups of the Pakistani population. The CYP2C9 genomic region holding important warfarin drug-metabolizing SNPs was sequenced from 159 individuals belong from five major ethnic groups of Pakistani population. The population genetic analyses of the high-quality sequences data was performed using Arlequin v3.5, DnaSP v6.12 and Network 5 resources. The data analyses unveiled that genetic variance among samples mainly arose from population-scale differentiation among these ethnic groups with global Fst of 0.78, P-value < 0.0001. The highest pairwise population genetic variation observed between Saraiki and Baloch groups based on different statistical tests. Whereas, uniform genetic composition across CYP2C9 loci was inferred among Punjabi, Pathan and Sindhi groups with minimal genetic differentiation. Several SNPs, including the previously reported warfarin associated variants, i.e. rs2860905, rs1799853 (CYP2C9*2) and rs72558189 (CYP2C9*14) were detected in these population groups with diverse allelic frequencies. Besides, a novel intronic SNP, i.e. not available in dbSNP and Ensemble databases, was identified for a Sindhi individual sample. This novel SNP predicted to influence the CYP2C9 alternative transcript splicing. The pharmacogeneticsassessment of the CYP2C9 genetic variations identified in current study may important to test against the warfarin efficacy for different ethnicity of Pakistani population.

Influence of CYP2D6 genetic polymorphism on pharmacokinetics of active moiety of tolterodine

Tolterodine is metabolized to an active 5-hydroxymethyl tolterodine (5-HMT) by CYP2D6. This study investigated the relationship between CYP2D6 genotypes and pharmacokinetics of tolterodine and its active metabolite in healthy Korean subjects. All volunteers were genotyped for CYP2D6 and divided into four different genotype groups (CYP2D6*wt/*wt [*wt = *1 or *2], CYP2D6*wt/*10, CYP2D6*10/*10, and CYP2D6*5/*10). Each subject received a single oral dose of tolterodine tartrate (2 mg) in single-dose phase of the study. After the single-dose phase of the study, the same subjects received a single oral dose of tolterodine tartrate (2 mg) once daily for 1 week during multiple-dose tolterodine administration phase. Plasma concentrations of tolterodine and 5-HMT were measured by using liquid chromatography-tandem mass spectrometry method. Our study demonstrated that plasma exposure of tolterodine in CYP2D6*10/*10 and CYP2D6*5/*10 group significantly increased, compared with CYP2D6*wt/*wt group (P < 0.001). The pharmacokinetic parameters of 5-HMT were not significantly different in relation to CYP2D6 genotype, as 5-HMT itself is also metabolized by CYP2D6. With regard to active moiety (tolterodine + 5-HMT), C_max and AUC_0-24 was significantly increased in CYP2D6*10/*10 group, compared with CYP2D6*wt/*wt group (P < 0.001). Thus, our study showed the pharmacokinetics of tolterodine and its active moiety was significantly different in relation to CYP2D6 genotype.

The influences of CYP2C9*1/*3 genotype on the pharmacokinetics of zolpidem

Zolpidem is predominantly metabolized by CYP3A4, and to a lesser extent by CYP2C9, CYP1A2, CYP2D6 and CYP2C19. The aim of this study was to identify the effects of CYP2C9*3 allele on the pharmacokinetics of zolpidem. Healthy male subjects were divided into two genotype groups, CYP2C9*1/*1 and CYP2C9*1/*3. They received a single oral dose of 5 mg zolpidem, and the plasma concentrations of zolpidem were determined up to 12 h after drug administration. In addition, since zolpidem is metabolized at a high rate by CYP3A4, the effect of CYP2C9*3 allele on the pharmacokinetics of zolpidem was also observed in the condition where CYP3A4 was sufficiently inhibited by the steady-state concentration of clarithromycin, a potent CYP3A4 inhibitor. For this, clarithromycin 500 mg was administered twice daily for 5 days. Plasma concentrations of zolpidem were determined using liquid chromatography-tandem mass spectrometry method. The overall pharmacokinetic parameters of zolpidem were not significantly different between two CYP2C9 genotypes. Even with the potent CYP3A4 inhibitor clarithromycin present at steady-state concentrations, there were no significant differences in the exposure of zolpidem, except for elimination half-life (t_1/2). In conclusion, our study suggests that CYP2C9*1/*3 genotype does not affect the plasma exposure of zolpidem.

Effects of genetic polymorphisms of CYP2C19 on the pharmacokinetics of zolpidem

Zolpidem is indicated for the short-term treatment of insomnia and it is predominantly metabolized by CYP3A4, and to a lesser extent by CYP2C19, CYP1A2, and CYP2C9. Therefore, we evaluated the effects of CYP2C19 genetic polymorphisms on the pharmacokinetics of zolpidem in healthy male subjects. Thirty-two male subjects were recruited and all subjects were classified into three groups according to their genotypes: CYP2C19EM (CYP2C19*1/*1, n = 12), CYP2C19IM (CYP2C19*1/*2 or *1/*3, n = 10), and CYP2C19PM (CYP2C19*2/*2, *2/*3 or *3/*3, n = 10). The pharmacokinetic parameters of zolpidem were compared in three CYP2C19 genotype groups after zolpidem administration with or without a CYP3A4 inhibitor at steady-state concentration. Plasma concentrations of zolpidem were determined up to 12 h after drug administration by liquid chromatography-tandem mass spectrometry method. The maximum plasma concentration (C_max) differed, but mean total area under the plasma concentration-time curve (AUC_inf), half-life (t_1/2), and apparent oral clearance (CL/F) of zolpidem administered alone did not significantly differ among the three different CYP2C19 genotype groups. Furthermore, when zolpidem was administered with a CYP3A4 inhibitor at steady-state concentration, there were no significant differences in any of the pharmacokinetic parameters of zolpidem in relation to CYP2C19 genotypes. In conclusion, we did not find any evidence for the impact of CYP2C19 genetic polymorphisms on the pharmacokinetic parameters of zolpidem.

Simultaneous determination of tolterodine and its two metabolites, 5-hydroxymethyltolterodine and N-dealkyltolterodine in human plasma using LC-MS/MS and its application to a pharmacokinetic study

Tolterodine is a nonselective muscarinic antagonist that is indicated for the overactive urinary bladder and other urinary difficulties. We developed and validated a simple, rapid and sensitive high-performance liquid chromatography analytical method utilizing tandem mass spectrometry (LC-MS/MS) for the quantitation of tolterodine and its major metabolites, 5-hydroxymethyltolterodine (5-HMT) and N-dealkyltolterodine (NDT), in human plasma. After liquid-liquid extraction with methyl t-butyl ether, chromatographic separation of the three analytes was achieved using a reversed-phase Luna Phenyl-hexyl column (100 × 2.0 mm, 3 μm particles) with a mobile phase of 10 mM ammonium formate buffer (pH 3.5)-methanol (10:90, v/v) and quantified by MS/MS detection in electrospray ionization (ESI) positive ion mode. The retention time of tolterodine, 5-HMT, NDT, and internal standard (IS) were 1.4, 1.24, 1.33, and 1.26 min, respectively. The calibration curves were linear over a range of 0.025-10 ng/ml for tolterodine and 5-HMT, and 0.05-10 ng/ml for NDT. The lower limit of quantifications using 200 μl of human plasma was 0.025 ng/ml for tolterodine and 5-HMT, and 0.05 ng/ml for NDT. The mean accuracy and precision for intra- and inter-run validation of tolterodine, 5-HMT, and NDT were all within acceptable limits. These results showed that a simple, rapid and sensitive LC-MS/MS method for the quantification of tolterodine and its major metabolites in human plasma was developed. This method was successfully applied to a pharmacokinetic study in humans.

Effects of CYP2C9 genetic polymorphisms on the pharmacokinetics of celecoxib and its carboxylic acid metabolite

Celecoxib, a selective cyclooxygenase (COX)-2 inhibitor, is used for the treatment of rheumatoid arthritis and osteoarthritis. The predominant hepatic metabolism of celecoxib to celecoxib carboxylic acid (CCA) is mediated mainly by CYP2C9. We investigated the effects of the major CYP2C9 genetic variants in Asian populations, CYP2C9*3 and CYP2C9*13, on the pharmacokinetics of celecoxib and its carboxylic acid metabolite in healthy Korean subjects. A single 200-mg oral dose of celecoxib was given to 52 Korean subjects with different CYP2C9 genotypes: CYP2C9EM (n = 26; CYP2C9*1/*1), CYP2C9IM (n = 24; CYP2C9*1/*3 and *1/*13), and CYP2C9PM (n = 2; CYP2C9*3/*3). Celecoxib and CCA concentrations in plasma samples collected up to 48 or 96 h after drug intake were determined by HPLC-MS/MS. The mean area under the plasma concentration-time curve (AUC_0-∞) of celecoxib was increased 1.63-fold (P < 0.001), and the apparent oral clearance (CL/F) of celecoxib was decreased by 39.6% in the CYP2C9IM genotype group compared with that of CYP2C9EM (P < 0.001). The overall pharmacokinetic parameters for celecoxib in CYP2C9*1/*13 subjects were similar to those in CYP2C9*1/*3 subjects. Two subjects with CYP2C9PM genotype both showed markedly higher AUC_0-∞, prolonged half-life, and lower CL/F for celecoxib than did subjects with CYP2C9EM and IM genotypes. CYP2C9*3 and CYP2C9*13 variant alleles significantly affected the plasma concentration of celecoxib.