Frequency of CYP2C9 alleles in Koreans and their effects on losartan pharmacokinetics

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 CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide in healthy subjects

Gliclazide metabolism is mediated by genetically polymorphic CYP2C9 and CYP2C19 enzymes. We investigated the effects of CYP2C9 and CYP2C19 genetic polymorphisms on the pharmacokinetics and pharmacodynamics of gliclazide. Twenty-seven Korean healthy volunteers were administered a single oral dose of gliclazide 80 mg. The plasma concentration of gliclazide was quantified for the pharmacokinetic analysis and plasma concentrations of glucose and insulin were measured as pharmacodynamic parameters. The pharmacokinetics of gliclazide showed a significant difference according to the number of defective alleles of combined CYP2C9 and CYP2C19. The two defective alleles group (group 3) and one defective allele group (group 2) showed 2.34- and 1.46-fold higher AUC_0-∞ (P < 0.001), and 57.1 and 32.3% lower CL/F (P < 0.001), compared to those of the no defective allele group (group 1), respectively. The CYP2C9IM-CYP2C19IM group had AUC_0-∞ increase of 1.49-fold (P < 0.05) and CL/F decrease by 29.9% (P < 0.01), compared with the CYP2C9 Normal Metabolizer (CYP2C9NM)-CYP2C19IM group. The CYP2C9NM-CYP2C19PM group and CYP2C9NM-CYP2C19IM group showed 2.41- and 1.51-fold higher AUC_0-∞ (P < 0.001), and 59.6 and 35.4% lower CL/F (P < 0.001), compared to those of the CYP2C9NM-CYP2C19NM group, respectively. The results represented that CYP2C9 and CYP2C19 genetic polymorphisms significantly affected the pharmacokinetics of gliclazide. Although the genetic polymorphism of CYP2C19 had a greater effect on the pharmacokinetics of gliclazide, the genetic polymorphism of CYP2C9 also had a significant effect. On the other hand, plasma glucose and insulin responses to gliclazide were not significantly affected by the CYP2C9-CYP2C19 genotypes, requiring further well-controlled studies with long-term dosing of gliclazide in diabetic patients.

Dosage exploration of meloxicam according to CYP2C9 genetic polymorphisms based on a population pharmacokinetic-pharmacodynamic model

BACKGROUND

Meloxicam, used for treating inflammatory diseases, shows large differences in metabolism according to CYP2C9 genetic polymorphisms; however, there are few studies on dose regimen setting based on quantitative predictions.

OBJECTIVE

The aim of this study was to determine the appropriate meloxicam dose regimen for each genotype through population pharmacokinetic-pharmacodynamic modeling of meloxicam by considering CYP2C9 genetic polymorphisms.

METHODS

For modeling, previously reported pharmacokinetic (plasma concentration)-pharmacodynamic (inhibition of thromboxane B₂ generation) data of meloxicam were collected for CYP2C9 genetic polymorphisms (n = 43). And these data were mainly used in the modeling process. Through simulations of the established models, steady-state pharmacokinetic-pharmacodynamic profiles were obtained according to meloxicam multiple exposures for each CYP2C9 genotype, and predictions were made based on dose regimen changes.

RESULTS

Genetic polymorphisms of CYP2C9 were identified as key covariates that significantly affected pharmacokinetic variability of meloxicam between individuals. The developed meloxicam population pharmacokinetic-pharmacodynamic model predicted pharmacokinetic results of the 7.5 mg meloxicam administration groups (n = 26) for CYP2C9*1/*1 and *1/*3 as an external validation. The results of model simulation revealed that the differences were 2.39-5.42 times for steady-state mean plasma concentrations and 1.21-1.71 times for the degree of inhibition of thromboxane B₂ generation following multiple exposures for CYP2C9*1/*1 versus *1/*13, *1/*3, and *3/*3. This suggested that thromboxane B₂ inhibition following increased plasma exposure to meloxicam differed significantly according to CYP2C9 genetic polymorphisms. The dose of meloxicam in CYP2C9*1/*13, *1/*3, and *3/*3 was randomly adjusted to 1.6-15 mg to approximate the mean thromboxane B₂ inhibition for CYP2C9*1/*1 at steady state, the dose intervals varied from 24 h to 48 h.

CONCLUSIONS

The results suggested that clinical dose adjustment of meloxicam would be necessary to account for CYP2C9 genetic polymorphisms and reduce side effects. This study suggests a clearer direction for setting up clinical therapy based on personalized medicine and quantitative predictions for meloxicam.

Clinical significance of the series of CYP2C9*non3 variants, an unignorable predictor of warfarin sensitivity in Chinese population

Backgrounds

Gene polymorphisms are critical for variations in warfarin dose. To date, more than 70 CYP2C9 alleles have been identified. This study was designed to clarify the clinical significance of CYP2C9*non-3 variants to warfarin sensitivity in Chinese Han patients.

Methods

The entire CYP2C9 gene region was sequenced in 1,993 individuals, and clinical data and VKORC1 genotypes were collected from 986 patients with atrial fibrillation treated with warfarin. The SKAT-O method was used to analyze the effects of CYP2C9*non-3 variants on warfarin sensitivity.

Results

A total of 20 CYP2C9 variants were identified, of which four were novel. Carriers with CYP2C9*non-3 variants may have lower warfarin dose requirements, and similar to CYP2C9*3, CYP2C9*non-3 variants are clearly relevant to warfarin-sensitive and highly sensitive responders.

Conclusion

Our results showed that, besides CYP2C9*3, the series of CYP2C9*non-3 variants is an unignorable predictor for warfarin sensitivity in Chinese population. From a safety consideration, people carried such variants may need a preferred choice of NOACs when they started anticoagulation therapy.

Physiologically based pharmacokinetic (PBPK) modeling of flurbiprofen in different CYP2C9 genotypes

The aim of this study was to establish the physiologically based pharmacokinetic (PBPK) model of flurbiprofen related to CYP2C9 genetic polymorphism and describe the pharmacokinetics of flurbiprofen in different CYP2C9 genotypes. PK-Sim® software was used for the model development and validation. A total of 16 clinical pharmacokinetic data for flurbiprofen in different CYP2C9 genotypes, dose regimens, and age groups were used for the PBPK modeling. Turnover number (k_cat) of CYP2C9 values were optimized to capture the observed profiles in different CYP2C9 genotypes. In the simulation, predicted fraction metabolized by CYP2C9, fraction excreted to urine, bioavailability, and volume of distribution were similar to previously reported values. Predicted plasma concentration-time profiles in different CYP2C9 genotypes were visually similar to the observed profiles. Predicted AUC_inf in CYP2C9*1/*2, CYP2C9*1/*3, and CYP2C9*3/*3 genotypes were 1.44-, 2.05-, and 3.67-fold higher than the CYP2C9*1/*1 genotype. The ranges of fold errors for AUC_inf, C_max, and t_1/2 were 0.84-1.00, 0.61-1.22, and 0.74-0.94 in development and 0.59-0.98, 0.52-0.97, and 0.61-1.52 in validation, respectively, which were within the acceptance criterion. Thus, the PBPK model was successfully established and described the pharmacokinetics of flurbiprofen in different CYP2C9 genotypes, dose regimens, and age groups. The present model could guide the decision-making of tailored drug administration strategy by predicting the pharmacokinetics of flurbiprofen in various clinical scenarios.

Physiologically based pharmacokinetic (PBPK) modeling of piroxicam with regard to CYP2C9 genetic polymorphism

Piroxicam is a non-steroidal anti-inflammatory drug used to alleviate symptoms of osteoarthritis and rheumatoid arthritis. CYP2C9 genetic polymorphism significantly influences the pharmacokinetics of piroxicam. The objective of this study was to develop and validate the piroxicam physiologically based pharmacokinetic (PBPK) model related to CYP2C9 genetic polymorphism. PK-Sim^® version 10.0 was used for the PBPK modeling. The PBPK model was evaluated by predicted and observed plasma concentration-time profiles, fold errors of predicted to observed pharmacokinetic parameters, and a goodness-of-fit plot. The turnover number (k_cat) of CYP2C9 was adjusted to capture the pharmacokinetics of piroxicam in different CYP2C9 genotypes. The population PBPK model overall accurately described and predicted the plasma concentration-time profiles in different CYP2C9 genotypes. In our simulations, predicted AUC_inf in CYP2C9*1/*2, CYP2C9*1/*3, and CYP2C9*3/*3 genotypes were 1.83-, 2.07-, and 6.43-fold higher than CYP2C9*1/*1 genotype, respectively. All fold error values for AUC, C_max, and t_1/2 were included in the acceptance criterion with the ranges of 0.57-1.59, 0.63-1.39, and 0.65-1.51, respectively. The range of fold error values for predicted versus observed plasma concentrations was 0.11-3.13. 93.9% of fold error values were within the two-fold range. Average fold error, absolute average fold error, and root mean square error were 0.93, 1.27, and 0.72, respectively. Our model accurately captured the pharmacokinetic alterations of piroxicam according to CYP2C9 genetic polymorphism.

Effects of CYP2C9*3 and *13 alleles on the pharmacokinetics and pharmacodynamics of glipizide in healthy Korean subjects

Glipizide is a second-generation sulfonylurea antidiabetic drug. It is principally metabolized to inactive metabolites by genetically polymorphic CYP2C9 enzyme. In this study, we investigated the effects of CYP2C9*3 and *13 variant alleles on the pharmacokinetics and pharmacodynamics of glipizide. Twenty-four healthy Korean volunteers (11 subjects with CYP2C9*1/*1, 8 subjects with CYP2C9*1/*3, and 5 subjects with CYP2C9*1/*13) were recruited for this study. They were administered a single oral dose of glipizide 5 mg. The plasma concentration of glipizide was quantified for pharmacokinetic analysis and plasma glucose and insulin concentrations were measured as pharmacodynamic parameters. The results represented that CYP2C9*3 and *13 alleles significantly affected the pharmacokinetics of glipizide. In subjects with CYP2C9*1/*3 and CYP2C9*1/*13 genotypes, the mean AUC_0-∞ were increased by 44.8% and 58.2%, respectively (both P < 0.001), compared to those of subjects with CYP2C9*1/*1 genotype, while effects of glipizide on plasma glucose and insulin levels were not significantly different between CYP2C9 genotype groups. In conclusion, individuals carrying the defective CYP2C9*3 and CYP2C9*13 alleles have markedly elevated plasma concentrations of glipizide compared with CYP2C9*1/*1 wild-type.

Pharmacogenomics of Hypertension in CKD: The CKD-PGX Study

Background

Patients with CKD often have uncontrolled hypertension despite polypharmacy. Pharmacogenomic drug-gene interactions (DGIs) may affect the metabolism or efficacy of antihypertensive agents. We report changes in hypertension control after providing a panel of 11 pharmacogenomic predictors of antihypertensive response.

Methods

A prospective cohort with CKD and hypertension was followed to assess feasibility of pharmacogenomic testing implementation, self-reported provider utilization, and BP control. The analysis population included 382 subjects with hypertension who were genotyped for cross-sectional assessment of DGIs, and 335 subjects followed for 1 year to assess systolic BP (SBP) and diastolic BP (DBP).

Results

Most participants (58%) with uncontrolled hypertension had a DGI reducing the efficacy of one or more antihypertensive agents. Subjects with a DGI had 1.85-fold (95% CI, 1.2- to 2.8-fold) higher odds of uncontrolled hypertension, as compared with those without a DGI, adjusted for race, health system (safety-net hospital versus other locations), and advanced CKD (eGFR <30 ml/min). CYP2C9-reduced metabolism genotypes were associated with losartan response and uncontrolled hypertension (odds ratio [OR], 5.2; 95% CI, 1.9 to 14.7). CYP2D6-intermediate or -poor metabolizers had less frequent uncontrolled hypertension compared with normal metabolizers taking metoprolol or carvedilol (OR, 0.55; 95% CI, 0.3 to 0.95). In 335 subjects completing 1-year follow-up, SBP (-4.0 mm Hg; 95% CI, 1.6 to 6.5 mm Hg) and DBP (-3.3 mm Hg; 95% CI, 2.0 to 4.6 mm Hg) were improved. No significant difference in SBP or DBP change were found between individuals with and without a DGI.

Conclusions

There is a potential role for the addition of pharmacogenomic testing to optimize antihypertensive regimens in patients with CKD.

Physiologically based pharmacokinetic modeling of candesartan related to CYP2C9 genetic polymorphism in adult and pediatric patients

Candesartan cilexetil is an angiotensin II receptor blocker and it is widely used to treat hypertension and heart failure. This drug is a prodrug that rapidly converts to candesartan after oral administration. Candesartan is metabolized by cytochrome P450 2C9 (CYP2C9) enzyme or uridine diphosphate glucurinosyltransferase 1A3, or excreted in an unchanged form through urine, biliary tract and feces. We investigated the effect of genetic polymorphism of CYP2C9 enzyme on drug pharmacokinetics using physiologically based pharmacokinetic (PBPK) modeling. In addition, by introducing the age and ethnicity into the model, we developed a model that can propose an appropriate dosage regimen taking into account the individual characteristics of each patient. To evaluate the suitability of the model, the results of a clinical trial on twenty-two healthy Korean subjects and their CYP2C9 genetic polymorphism data was applied. In this study, PK-Sim® was used to develop the PBPK model of candesartan.

Physiologically based pharmacokinetic (PBPK) modeling of meloxicam in different CYP2C9 genotypes

Meloxicam, a non-steroidal anti-inflammatory drug, is used for the treatment of rheumatoid arthritis and osteoarthritis. Cytochrome P450 (CYP) 2C9 and CYP3A4 are major and minor enzymes involved in the metabolism of meloxicam. Impaired enzyme activity of CYP2C9 variants increases the plasma exposures of meloxicam and the risk of adverse events. The objective of our study is to develop and validate the physiologically based pharmacokinetic (PBPK) model of meloxicam related to CYP2C9 genetic polymorphism using the PK-Sim^® software. In vitro k_cat of CYP2C9 was optimized in different CYP2C9 genotypes. The demographic and pharmacokinetic dataset for the development of the PBPK model was extracted from two previous clinical pharmacokinetic studies. Thirty-one clinical datasets, representing different dose regimens and demographic characteristics, were utilized to validate the PBPK model. The shapes of simulated plasma concentration-time profiles in each CYP2C9 genotype were visually similar to observed profiles. The predicted exposures (AUC_inf) of meloxicam in CYP2C9*1/*3, CYP2C9*1/*13, and CYP2C9*3/*3 genotypes were increased by 1.77-, 2.91-, and 8.35-fold compared to CYP2C9*1/*1 genotype, respectively. In all datasets for the development and validations, fold errors between predicted and observed pharmacokinetic parameters were within the two-fold error criteria. As a result, the PBPK model was appropriately established and properly described the pharmacokinetics of meloxicam in different CYP2C9 genotypes. This study is expected to contribute to reducing the risk of adverse events of meloxicam through optimization of meloxicam dosing in different CYP2C9 genotypes.

Comprehensive analysis of important pharmacogenes in Koreans using the DMET™ platform

Genetic polymorphisms of enzymes and transporters associated with the absorption, distribution, metabolism, and elimination (ADME) of drugs are one of the major factors that contribute to interindividual variations in drug response. In the present study, we aimed to elucidate the pharmacogenetic profiles of the Korean population using the Affymetrix Drug Metabolizing Enzyme and Transporters (DMET™) platform. A total of 1,012 whole blood samples collected from Korean subjects were genotyped using the DMET™ plus microarray. In total, 1,785 single nucleotide polymorphism (SNP) markers for 231 ADME genes were identified. The genotype and phenotype of 13 clinically important ADME genes implemented in the Clinical Pharmacogenetics Implementation Consortium guidelines were compared among different ethnic groups. Overall, the genotype frequencies of the Korean population were similar to those of the East Asian population. Several genes, notably CYP2C19 and VKORC1, showed marked differences in Koreans compared to Europeans (EURs) or Africans (AFRs). The percentage of CYP2C19 poor metabolizers was 15% in Koreans and less than 3% in EURs or AFRs. The frequencies of causative SNPs of the VKORC1 gene for the low warfarin dose phenotype were 90%, 60%, and 10% in Koreans, EURs and AFRs, respectively. Our findings can be utilized for optimal pharmacotherapy in Korean patients.

The impact of an URAT1 polymorphism on the losartan treatment of hypertension and hyperuricemia

BACKGROUND

This study was designed to evaluate the impact of polymorphisms in the urate transporter 1 (URAT1) gene on the uricosuric action of losartan therapy in hypertensive patients suffering from hyperuricemia.

METHODS

A MassARRAY approach was used to detect single nucleotide polymorphism (SNP) loci in the URAT1 and CYP2C9 genes (16 and 2 loci, respectively) in 111 patients with hypertension and hyperuricemia taking losartan and in 121 healthy controls. In addition, we compared serum urate (SUA) levels and other key clinical biochemistry indices between these two patient groups.

RESULTS

We detected significant differences between the two patient groups with respect to age, SUA, urea, creatine, triglycerides, high-density lipoprotein, low-density lipoprotein, and fasting plasma glucose (all p < 0.05). In addition, we found that hypertensive patients with hyperuricemia were more likely to exhibit the rs3825016(C/T) (36.9% vs 21.5%, p = 0.03), and we determined that a 2-week treatment course with losartan was associated with significant decreases in SUA values (p < 0.001).

CONCLUSION

Our findings indicate that the URAT1 rs3825016 polymorphism may influence the uricosuric action of losartan.

Influence of CYP2C9 Genetic Polymorphisms on the Pharmacokinetics of Losartan and Its Active Metabolite E-3174: A Systematic Review and Meta-Analysis

This study aimed to investigate the influence of CYP2C9 genetic polymorphisms on the pharmacokinetics of losartan and its active metabolite, E-3174, through a systematic review and meta-analysis. Eight studies published before March 2021 were included in this study. We used PubMed, the Cochrane Library, EMBASE, and Web of Science, based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The data analysis was conducted through Review Manager (RevMan), version 5.3, and R software. We found that healthy volunteers with CYP2C9*2 or *3 carriers had higher area under the curve (AUC_0-∞) of losartan (mean difference (MD) 0.17 μg·h/mL; 95% confidence intervals (CI): 0.04, 0.29) and lower AUC_0-∞ of E-3174 (MD −0.35 μg·h/mL; 95% CI: −0.62, −0.08) than those with CYP2C9*1/*1. Subjects with CYP2C9*2 or *3 carriers showed lower maximum concentration (C_max) of E-3174 than those with CYP2C9*1/*1 (MD −0.13 μg/mL; 95% CI: −0.17, −0.09). For half-life, subjects with CYP2C9*2 or *3 carriers had longer half-lives of losartan and E-3174 than those with CYP2C9*1/*1 (MD 0.47 h; 95% CI: 0.32, 0.61 and MD 0.68 h; 95% CI: 0.44, 0.92, respectively). This meta-analysis suggests that the pharmacokinetics of losartan and E-3174 are associated with the CYP2C9 polymorphisms

Pharmacogenetics of tamoxifen therapy in Asian populations: from genetic polymorphism to clinical outcomes

BACKGROUND

Compared with western countries, Asian breast cancer patients have unique pathological and biological characteristics. Most of them are premenopausal women with HR positive. Tamoxifen as the first-line drug for premenopausal women with HR+ is involved in multiple enzymes and transporters during metabolizing and transporting process. Variants that cause decreased or inactive gene products leading to abnormal responses in tamoxifen therapy have well been studied in western countries, whereas such information is much less reported in Asian populations.

OBJECTIVE

In order to elucidate the relationship between genetic variants and tamoxifen-induced individual drug reactions in different Asian populations and further identify genotypes/phenotypes with potential therapeutic significance.

METHODS

We reviewed the frequencies of genetic variants in major enzymes and transporter genes involved in the metabolism and transport of tamoxifen across Asian populations as well as significant correlations between genotypes/metabolic phenotypes and metabolites concentrations or BC clinical outcomes.

RESULTS

Significant inter-ethnic differences in allele frequencies was found among Asian populations, such as CYP2D6*4, *10, *41, CYP2C9*2, ABCB1 C3435T and SLCO1B1*5, and CYP2D6*10/*10 is the most common genotype correlated with adverse clinical outcomes. Moreover, we summarized the barriers and controversies of implementing pharmacogenetics in tamoxifen therapy and concluded that more population-specific pharmacogenetic studies are needed in the future.

CONCLUSION

This review revealed more systematic pharmacogenomics of genes involved in the metabolism and transport besides CYP2D6, are required to optimize the genotyping strategies and guide the personalized tamoxifen therapy in Asian populations.

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.

Polymorphic analysis of CYP2C9 gene in Vietnamese population

Genetic variations in CYP2C9 are associated to inter-individual variability of drugs metabolism and response. The only report has been done previously mainly focusing on the common variant alleles of CYP2C9 in Vietnamese Kinh subjects. However, little is known about the complete spectrum of this gene polymorphism in different ethnic groups of Vietnam. We sequenced the promoter region and all exons of CYP2C9 in 100 healthy unrelated Vietnamese Kinh subjects. Additionally, common CYP2C9 variants, *2 and *3, were also analyzed by RFLP-PCR in extra 194 Kinh subjects and 279 of other four ethnic groups in Vietnam. The results of these common variants observed from five ethnic groups were compared with other populations in the world. Seven previously reported alleles and two genotypes were determined in Kinh subjects. The percentage of CYP2C9*1 and CYP2C9*3 alleles are 96.5 and 3.5%, respectively. We found one novel non-synonymous variant in exon 7 leading to amino acid change at 363 position from proline to histidine. Functional analysis by SIFT and Polyphen-2 indicated that this mutation is intolerant and probably damaging. Prevalence of CYP2C9*2 observed in Vietnamese population was significantly lower compared with that of other populations in the South and West of Asia as well as in Europe. This study provides information of genetic distribution pattern of CYP2C9 in Vietnamese, which would be useful for optimizing drug therapies in Vietnam.

Influence of CYP2C9 and COX-2 Genetic Polymorphisms on Clinical Efficacy of Non-Steroidal Anti-Inflammatory Drugs in Treatment of Ankylosing Spondylitis

Background

The aim of this study was to evaluate the relationships of CYP2C9 and COX-2 genetic polymorphisms with therapeutic efficacy of non-steroidal anti-inflammatory drugs (NSAIDs) in treatment of ankylosing spondylitis (AS).

Material/Methods

We enrolled 130 AS inpatients and outpatients in the Arthritis and Rheumatism Department of Peking University First Hospital and 106 healthy people getting routine check-ups between September 2013 and July 2014. CYP2C9 and COX-2 genetic polymorphisms were detected by PCR-RFLP. All AS patients underwent medical treatment and 12-week follow-up treatment. Score differences of BASDAI, ASAS20, ASAS50, and ASAS70 for AS patients with different genotypes before and after treatment were compared.

Results

In terms of COX-2-1290A/G and -1195G/A gene polymorphism genotype and allele frequency, the case group and control group were obviously different (all P<0.05), but CYP2C9*3 polymorphism genotype and allele frequency were not statistically different between the 2 groups (P>0.05). AS patients had improved BASDAI, ASAS20, ASAS50, and ASAS70 scores after they received NSAID treatment (all P<0.05). Furthermore, the efficacy of NSAID in treatment of AS and COX-2 gene −1290A/G and −1195G/A polymorphism were associated (all P<0.05), but it is not associated with CYP2C9 *3 polymorphism (all P>0.05).

Conclusions

COX-2-1290A/G and -1195G/A polymorphism may increase AS risk and they both can be considered as biological indicators for prediction of efficacy of NSAIDs in treatment of AS.

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.

Genetic variability of CYP2C9*2 and CYP2C9*3 in seven indigenous groups from Mexico

Aim: CYP2C9 is one of the major drug metabolizing enzymes, however, little is known about polymorphisms in CYP2C9 gene and pharmacological implications in Mexican indigenous populations. Thus, frequencies of CYP2C9*2 and CYP2C9*3 alleles were evaluated in indigenous groups located in northwest (Cora), center (Mazahua and Teenek), south (Chatino and Mixteco) and southeast (Chontal and Maya) regions Mexico. Materials & methods: Allelic discrimination was performed by real-time PCR. Results: CYP2C9*2 allele was found only in Chontal and Maya groups, despite the low contribution of Caucasian component in these populations. CYP2C9*3 allele was present in all populations except in Mazahua, showing a wide genetic variability in the studied populations. Interestingly, we found significant differences between indigenous groups in CYP2C9*3 allele, even in groups located at the same region and belonging to the same linguistic family. Conclusion: These results contribute to laying the pharmacogenetic bases in Mexico, in addition to improving treatment, taking into account the genetic interethnic differences.

Effects of CYP2C9 genetic polymorphisms on the pharmacokinetics of zafirlukast

Zafirlukast, a cysteinyl leukotriene receptor antagonist, is indicated for the treatment of patients with mild to moderate asthma. Zafirlukast is metabolized mainly by CYP3A4 and CYP2C9. We investigated the effects of the major CYP2C9 variant alleles in Asian populations, CYP2C9*3 and CYP2C9*13, on the pharmacokinetics of zafirlukast in healthy Korean subjects. A single 20-mg oral dose of zafirlukast was given to 23 Korean male subjects divided into two genotype groups according to CYP2C9 genotypes, CYP2C9EM (n = 11; CYP2C9*1/*1) and CYP2C9IM (n = 12; 9 and 3 carriers of CYP2C9*1/*3 and *1/*13, respectively). Zafirlukast concentrations were determined using a validated HPLC-MS/MS analytical method in plasma samples collected after the drug intake. Compared with the CYP2C9EM group, the Cmax and AUCinf of zafirlukast in the CYP2C9IM group were 1.44- and 1.70-fold higher, respectively (p < 0.01 and p < 0.0001). The CL/F of zafirlukast was 42.8 % lower in the CYP2C9IM group compared with the CYP2C9EM group (p < 0.001). Slightly higher Cmax and AUC, and lower CL/F of zafirlukast were observed in subjects with the CYP2C9*1/*13 genotype compared with the CYP2C9*1/*3 genotype subjects. CYP2C9*3 and CYP2C9*13 alleles significantly affected the plasma concentrations of zafirlukast.

Comparison of the effects of amlodipine and losartan on blood pressure and diurnal variation in hypertensive stroke patients: a prospective, randomized, double-blind, comparative parallel study

BACKGROUND

Lowering blood pressure (BP) and reducing diurnal variation are important for the prevention of stroke in patients with hypertension.

OBJECTIVE

This study was conducted to compare the BP-lowering and diurnal BP variation effects of amlodipine and losartan on acute stroke patients.

METHODS

Seventy-seven hypertensive patients with acute stroke were enrolled in this randomized, double-blind, single-center clinical trial. They were randomly assigned to receive either amlodipine or losartan daily. To evaluate whether amlodipine was noninferior to losartan, ambulatory BP monitoring was performed before the drugs were first administered and at the end of week 8. BP variables analyzed included the mean awake, sleep, morning, evening, and prewake BP values; the nocturnal dipping status; and the morning surge.

RESULTS

Thirty-nine patients in the amlodipine group and 38 patients in the losartan group completed the follow-up. In the baseline characteristics, mean age was 63.6 years, and 68.8% were male. In the intention-to-treat analysis, the mean (SD) systolic BP decreased 14.82 (11.71) mm Hg in the amlodipine group and 13.11 (12.69) mm Hg in the losartan group, and amlodipine proved noninferior to losartan (mean difference, 1.71 mm Hg [95% CI, -3.83 to 7.26]). However, in the per-protocol analysis, noninferiority was not proven (BP reduction, 16.06 [11.33] vs 17.17 [11.85] mm Hg; mean difference, -1.11 mm Hg [95% CI, -6.88 to 4.65]). Amlodipine had a greater tendency than losartan to produce a blunt morning surge.

CONCLUSIONS

The noninferiority of amlodipine was not confirmed by the per-protocol analysis. However, amlodipine showed a favorable effect on the morning surge. ClinicalTrials.gov identifier: NCT01830517.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Genotype-phenotype correlation of cytochrome P450 2C9 polymorphism in Indian National Capital Region

Identification of polymorphism of cytochrome P450 2C9 (CYP2C9) enzymes in different ethnic populations is important to understand the differences in clinical responses to drugs. This study determines the CYP2C9 genetic polymorphism in Indian National Capital Region and correlates the phenotype-genotype. Losartan (25 mg) was administered to 107 volunteers to assess CYP2C9 activity, and, on the basis of results, volunteers were categorized as rapid and poor metabolizers. Molecular typing of CYP2C9*1 (wild type), CYP2C9*2, and CYP2C9*3 (the most common variant) was carried out by single-base primer extension technology for 37 subjects, of which 9 were poor metabolizers, and 28 were rapid metabolizers. 14.28 % of the studied population was identified as poor metabolizer for the category of drugs metabolized by CYP2C9. Significant difference was observed between the mean ratio (drug/metabolite) of poor (11.38 ± 5.88) and rapid (1.18 ± 1.11) drug metabolizers. The study suggests that phenotyping of CYP2C9 is desirable before enrollment of subjects for clinical trials or for deciding drug dose regimen as 14.28 % of study population was found to be poor metabolizer for the category of drugs metabolized by CYP2C9. This study establishes phenotype-genotype correlation, and proposes to use genotyping or phenotyping to evaluate the status of drug metabolizing capacity of CYP2C9 as a primary screening procedure before enrolling subjects in clinical trials or in clinical practice.

Distribution of CYP2C9*13 allele in the Chinese Han and the long-range haplotype containing CYP2C9*13 and CYP2C19*2

Cytochrome P450 2C9 (CYP2C9) and CYP2C19, located in tandem on chromosome 10q23-24, are known as genetically polymorphic. CYP2C9*13 is an important CYP2C9 variant in Asian populations, and is correlated with the reduced plasma clearance of some clinically important drugs. In this research, the allele frequency of CYP2C9*13 was determined to be 0.42% (95% CI of 0.17% to 0.86%) in 839 Chinese Han, male subjects. All detected subjects with CYP2C9*13 carry the CYP2C19*2 allele, too. Sequencing results infer the CYP2C9*13 haplotype, which contains eight linked SNPs, originates from the CYP2C9*1B haplotype group. CYP2C9*1B has been reported to be linked with CYP2C19*2. These indicate a long-range haplotype containing the CYP2C9*13 and CYP2C19*2 mutation, which means most CYP2C9*13 carriers will carry the CYP2C19*2 allele and the six SNPs of the CYP2C9*1B haplotype group, and may have more reduced intrinsic clearance of drugs such as phenytoin, tolbutamide and chlorpropamide that are metabolized by both CYP2C9 and CYP2C19.

Impact of genetic polymorphisms in CYP2C9 and CYP2C19 on the pharmacokinetics of clinically used drugs

Human cytochrome P450 (CYP) is a superfamily of hemoproteins which oxidize a number of endogenous compounds and xenobiotics. The human CYP2C subfamily consists of four members: CYP2C8, CYP2C9, CYP2C18 and CYP2C19. CYP2C9 and CYP2C19 are important drug-metabolizing enzymes and together metabolize approximately 20% of therapeutically used drugs. Forty-two allelic variants for CYP2C9 and 34 for CYP2C19 have been reported. The frequencies of these variants show marked inter-ethnic variation. The functional consequences of genetic polymorphisms have been examined, and many studies have shown the clinical importance of these polymorphisms. Current evidence suggests that taking the genetically determined metabolic capacity of CYP2C9 and CYP2C19 into account has the potential to improve individual risk/benefit relationships. However, more prospective studies with clinical endpoints are needed before the paradigm of "personalized medicine" based on the variants can be established. This review summarizes the currently available important information on this topic.