Effects of theCYP2C9*13allele on the pharmacokinetics of losartan in healthy male subjects

Optimisation of warfarin-dosing algorithms for Han Chinese patients with CYP2C9*13 variants

BACKGROUND

Existing pharmacogenetic algorithms cannot fully explain warfarin dose variability in all patients. CYP2C9*13 is an important allelic variant in the Han Chinese population. However, adjustment of warfarin dosing in CYP2C9*13 variant carriers remains unclear. To the best of our knowledge, this study is the first to assess the effects of adjusting warfarin dosages in Han Chinese patients harbouring CYP2C9*13 variants.

METHODS

In total, 971 warfarin-treated Han Chinese patients with atrial fibrillation were enrolled in this study. Clinical data were collected, and CYP2C9*2, *3, *13 and VKORC1-1639 G > A variants were genotyped. We quantitatively analysed the effect of CYP2C9*13 on warfarin maintenance dose and provided multiplicative adjustments for CYP2C9*13 using validated pharmacogenetic algorithms.

RESULTS

Approximately 0.6% of the Han Chinese population carried CYP2C9*13 variant, and the genotype frequency was between those of CYP2C9*2 and CYP2C9*3. The warfarin maintenance doses were significantly reduced in CYP2C9*13 carriers. When CYP2C9*13 variants were not considered, the pharmacogenetic algorithms overestimated warfarin maintenance doses by 1.03-1.16 mg/d on average. The actual warfarin dose in CYP2C9*13 variant carriers was approximately 40% lower than the algorithm-predicted dose. Adjusting the warfarin-dosing algorithm according to the CYP2C9*13 allele could reduce the dose prediction error.

CONCLUSION

Our study showed that the algorithm-predicted doses should be lowered for CYP2C9*13 carriers. Inclusion of the CYP2C9*13 variant in the warfarin-dosing algorithm tends to predict the warfarin maintenance dose more accurately and improves the efficacy and safety of warfarin administration in Han Chinese patients.

Changes in Pharmacokinetics and Pharmacodynamics of Losartan in Experimental Diseased Rats Treated with Curcuma longa and Lepidium sativum

The current study investigated “pharmacodynamics and pharmacokinetics interactions” of losartan with Curcuma longa (CUR) and Lepidium sativum (LS) in hypertensive rats. Hypertension was induced by oral administration of L-NAME (40 mg/kg) for two weeks. Oral administration of CUR or LS shows some substantial antihypertensive activity. The systolic blood pressure (SBP) of hypertensive rats was decreased by 7.04% and 8.78% 12 h after treatment with CUR and LS, respectively, as compared to rats treated with L-NAME alone. LS and CUR display the ability to potentiate the blood pressure-lowering effects of losartan in hypertensive rats. A greater decrease in SBP, by 11.66% and 13.74%, was observed in hypertensive rats treated with CUR + losartan and LS + losartan, respectively. Further, both the investigated herbs, CUR and LS, caused an increase in plasma concentrations of losartan in hypertensive rats. The AUC0-t, AUC0-inf and AUMC0-inf of losartan were increased by 1.25-fold, 1.28-fold and 1.09-fold in hypertensive rats treated with CUR + losartan. A significant (p < 0.05) increase in AUC0-t (2.41-fold), AUC0-inf (3.86-fold) and AUMC0-inf (8.35-fold) of losartan was observed in hypertensive rats treated with LS + losartan. The present study affirms that interactions between CUR or LS with losartan alter both “pharmacokinetics and pharmacodynamics” of the drug. Concurrent administration of losartan with either CUR or LS would require dose adjustment and intermittent blood pressure monitoring for clinical use in hypertensive patients. Additional investigation is necessary to determine the importance of these interactions in humans and to elucidate the mechanisms of action behind these interactions.

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.

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

Effects of rare CYP2C9 alleles on stable warfarin doses in Chinese Han patients with atrial fibrillation

Aim: Gene polymorphisms are critical in warfarin dosing variation. Here, the role of rare CYP2C9 alleles on warfarin doses in Chinese Han patients was investigated. Methods: A retrospective study recruited 681 warfarin treated atrial fibrillation patients. The genetic and clinical data were collected. Dose-related variables were selected by univariate analyses and the warfarin-dosing algorithm was derived by multivariate regression analysis. Results: Three rare CYP2C9 alleles (CYP2C9*13, *16 and *60) were associated with lower stable doses. Inclusion of the rare CYP2C9 alleles in the prediction model added an extra 3.7% warfarin dose predictive power. Conclusion: CYP2C9*13, *16 and *60 was associated with lower stable warfarin doses in Chinese patients. The algorithm including rare CYP2C9 alleles tends to more accurately predict stable warfarin doses.

Impact of CYP2C19 and CYP2C9 gene polymorphisms on sodium valproate plasma concentration in patients with epilepsy

BACKGROUND

Valproic acid (VPA) is a broad spectrum anticonvulsant drug, which could be partially metabolised by cytochrome P450 (CYP) 2C9 and 2C19 enzymes. This study was designed to investigate the relationship between CYP2C19 and CYP2C9 gene polymorphisms and the plasma concentrations of VPA in subjects with epilepsy.

METHODS

Eighty-three subjects with epilepsy aged 18-92 years were enrolled in this study. All were treated with sustained-release VPA monotherapy. Based on the genotypes of CYP2C19 and the ability to metabolise substrates, the subjects were divided into poor metabolisers, intermediate metabolisers and extensive metabolisers. Sanger sequencing was used to detect the genotypic and allelic frequencies of CYP2C19 (*1, *2 and *3) and CYP2C9 (*13) of the patients. Automatic immunity analysis was used to find steady-state trough plasma concentrations of VPA. By adjusting the plasma concentrations of VPA with body weight and total daily dose of VPA, the concentration-to-dose ratio of VPA (CDRV) was obtained. Data were analysed using SPSS software.

RESULTS

The genetic frequencies of CYP2C19*2, CYP2C19*3 and CYP2C9*13 were 33.1%, 3.0% and 5.4%, respectively, among patients with epilepsy from Yunnan province, China who used VPA therapy. The CDRV was significantly lower in the CYP2C19 extensive metabolisers (3.33±1.78) than it was in the CYP2C19 intermediate metabolisers (4.45±1.42) and the CYP2C19 poor metabolizers (6.64±1.06). The CYP2C19*2 and CYP2C19*3 alleles were correlated with the plasma VPA concentration, while the CYP2C9*13 allele had no effect on the plasma VPA concentration (p=0.809).

CONCLUSIONS

The genetic polymorphisms of CYP2C19 significantly affect the VPA plasma concentration, and the dosage of VPA for intermediate and poor metabolisers could be lower than for extensive metabolisers. CYP2C9*13 carrier was not closely related to plasma concentrations of VPA in patients with epilepsy.

Potential pharmacodynamic and pharmacokinetic interactions of Nigella Sativa and Trigonella Foenum-graecum with losartan in L-NAME induced hypertensive rats

The objective of this investigation was to study whether Nigella Sativa and Trigonella Foenum-graecum, could modulate the losartan pharmacodynamic (PD) and pharmacokinetic (PK) in experimental L-NAME induced hypertensive rats. For in vivo study, the systolic blood pressure (SBP) of rats was measured by the “tail-cuff system” after the treatment of rats with herb alone and herb + losartan in hypertensive rats. The SBP of rats treated with L-NAME + losartan also recorded. For the PK study, blood samples were obtained for up to 12 h to determine the concentrations of the drug, and various PK parameters were calculated. The data displayed that the SBP was significantly (p < 0.05) decreased in the rats when administered with L-NAME + N. Sativa or L-NAME + T. Foenum-graecum in contrast to the rats administered with L-NAME alone. A more prominent decline (p < 0.05) in SBP was detected in rats administered with L-NAME + N. Sativa + losartan and L-NAME + T. Foenum-graecum + losartan. In a PK study, higher losartan C_max and AUC_0-t were noted in rats treated with N. Sativa + losartan and T. Foenum-graecum + losartan, although the difference was not significant in contrast to the control group. This study proposed that the interaction between N. Sativa & losartan and T. Foenum-graecum & losartan could take place on concurrent administration; consequently, the dose of losartan may need to be accustomed when they are utilized simultaneously.

Effects of Ginkgo leaf tablets on the pharmacokinetics of losartan and its metabolite EXP3174 in rats and its mechanism

CONTEXT

Ginkgo leaf tablets (GLTs) and losartan are often simultaneously used for the treatment of hypertension in Chinese clinics. However, the herb-drug interaction between GLT and losartan is still unknown.

OBJECTIVE

This study investigates the effects of GLT on the pharmacokinetics of losartan and its metabolite EXP3174 in rats and its potential mechanism.

MATERIALS AND METHODS

The pharmacokinetic profiles of losartan and EXP3174 of orally administered losartan (10 mg/kg) with or without GLT pretreatment (80 mg/kg/day for 10 days) in Sprague-Dawley rats were determined. In vitro, the effects of GLT on the metabolic stability of losartan were investigated with rat liver microsomes.

RESULTS

The C_max (1.22 ± 0.25 vs 1.85 ± 0.37 μg/mL) and the AUC_(0-t) (6.99 ± 1.05 vs 11.94 ± 1.79 mg·h/L) of losartan increased significantly (p < 0.05) with GLT pretreatment, while the C_max (1.05 ± 0.19 vs 0.72 ± 0.12 μg/mL) of EXP3174 decreased significantly (p < 0.05) compared to the control. The t_1/2 of losartan was prolonged significantly from 3.94 ± 0.62 to 4.75 ± 0.52 h (p < 0.05). The metabolic stability of losartan was increased from 37.4 min to 59.6 min with GLT pretreatment.

DISCUSSION AND CONCLUSIONS

The results indicate that GLT might increase the plasma concentration of losartan and decrease the concentration of EXP3174 through inhibiting the metabolism of losartan.

Pharmacogenetic approach to losartan in Marfan patients: a starting point to improve dosing regimen?

BACKGROUND

Losartan is under evaluation for managing Marfan patients with aortic root dilatation. Cytochrome P450 (CYP) enzymes convert losartan to E3174 active metabolite. The aim of this study is to describe the distribution of CYP2C9*2, CYP2C9*3, CYP3A4*22 and CYP3A5*3 defective alleles, according to losartan tolerance in paediatric Marfan patients.

METHODS

We genotyped 53 paediatric Marfan patients treated with losartan. The rate of aortic root dilatation was evaluated using the delta z-score variation. Differences in tolerated losartan daily doses with respect to CYP metabolic classes were assessed through the Kruskal-Wallis test.

RESULTS

The losartan daily dose spans from 0.16 to 2.50 mg/kg (median 1.10 mg/kg). As we expect from the pharmacokinetics pathway, we observe highest tolerated dose in CYP2C9 poor metabolisers (median 1.50 mg/kg, interquartile range 1.08-1.67 mg/kg); however, this difference is not statistically significant.

CONCLUSIONS

The optimal dose of angiotensin receptor blocker is not known, and no data are available about losartan pharmacogenetic profile in Marfan syndrome; we have proposed a strategy to tackle this issue based on evaluating the major genetic polymorphisms involved in the losartan conversion into active carboxylic acid metabolite. Further studies are needed to support the use of genetic polymorphisms as predictors of the right dose of losartan.

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.

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.

In vitro and in vivo characterization of 13 CYP2C9 allelic variants found in Chinese Han population

Our previous study detected totally 35 CYP2C9 allelic variants in 2127 Chinese subjects, of whom 21 novel alleles were reported for the first time in Chinese populations. The aim of the present study was to characterize the 13 CYP2C9 allelic variants both in vitro and in vivo. Different types of CYP2C9 variants were highly expressed in COS-7 cells, and 50 μM tolbutamide was added as the probing substrate to evaluate their metabolic abilities in vitro. Subsequently, the concentrations of tolbutamide and its metabolite in the plasma and urine within individuals with different types of genotypes were determined by HPLC to evaluate the catalytic activity of the 13 mutant CYP2C9 proteins in vivo. Our results showed that compared with *1/*1 wild-type subjects, subjects with *1/*40 genotype showed increased oral clearance (CL/F), whereas individuals with *1/*3, *1/*13, *3/*3, *3/*13, *1/*16, *1/*19, *1/*34, *1/*42, *1/*45, *1/*46, and *1/*48 genotype exhibited significantly decreased CL/F, and those with *1/*27, *1/*29, *1/*40, and *1/*41 genotype presented similar CL/F value. When expressed in COS-7 cells, the CYP2C9 variants showed similar pattern to the results in clinical study. The study suggests that, besides two typical defective alleles, *3 and *13, seven CYP2C9 allelic variants (*16, *19, *34, *42, *45, *46, and *48) cause defective effects on the enzymatic activities both in vitro and in vivo. In clinic, patients with these defective alleles should be paid close attention to.

In vitro assessment of 36 CYP2C9 allelic isoforms found in the Chinese population on the metabolism of glimepiride

Of the 57 reported CYP2C9 alleles, to date, 36 of them have been identified in the Chinese population. The aim of this study was to assess the catalytic characteristics of these allelic isoforms and their effects on the metabolism of glimepiride in vitro. Baculovirus-mediated expressing system was used to highly express wild-type and the 35 CYP2C9 allelic variants in insect cell microsomes. Then, the enzymatic characteristics of each variant were evaluated using glimepiride as the substrate. Reactions were performed at 37°C with the insect microsomes and 0.125-10 μM glimepiride for 40 min. After termination, the products were extracted and used for signal collection by LC-MS/MS. Of the 36 tested CYP2C9 allelic isoforms, only four variants (CYP2C9.40, CYP2C9.47, CYP2C9.51 and CYP2C9.54) exhibited similar relative clearance values to that of wild-type CYP2C9.1. In addition, one variant (CYP2C9.36) showed a higher intrinsic clearance value than the wild-type protein, while the remaining 30 CYP2C9 allelic isoforms exhibited significantly decreased clearance values (from 0.1% to 87.2%) compared to CYP2C9.1. This study provided the most comprehensive data on the enzymatic activities of all reported CYP2C9 variants in the Chinese population with regard to the commonly used antidiabetic drug, glimepiride. Our results indicate that most of the tested rare alleles significantly decrease the catalytic activity of CYP2C9 variants towards glimepiride hydroxylation in vitro.

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.

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.

Distal effect of amino acid substitutions in CYP2C9 polymorphic variants causes differences in interatomic interactions against (S)-warfarin

Cytochrome P450 2C9 (CYP2C9) is crucial in excretion of commonly prescribed drugs. However, changes in metabolic activity caused by CYP2C9 polymorphisms inevitably result in adverse drug effects. CYP2C9*2 and *3 are prevalent in Caucasian populations whereas CYP2C9*13 is remarkable in Asian populations. Single amino acid substitutions caused by these mutations are located outside catalytic cavity but affect kinetic activities of mutants compared to wild-type enzyme. To relate distal effects of these mutations and defective drug metabolisms, simulations of CYP2C9 binding to anti-coagulant (S)-warfarin were performed as a system model. Representative (S)-warfarin-bound forms of wild-type and mutants were sorted and assessed through knowledge-based scoring function. Interatomic interactions towards (S)-warfarin were predicted to be less favorable in mutant structures in correlation with larger distance between hydroxylation site of (S)-warfarin and reactive oxyferryl heme than wild-type structure. Using computational approach could delineate complication of CYP polymorphism in management of drug therapy.

Ethnic variability in the plasma exposures of OATP1B1 substrates such as HMG-CoA reductase inhibitors: a kinetic consideration of its mechanism

Because the plasma exposure levels of rosuvastatin in Asians are generally twice those in Caucasians, the starting dose for Asians in the United States is set to half of that for non-Asians. However, the precise role of ethnicity in the clearance of rosuvastatin has not yet been clarified. This review focuses on ethnic variability in the clinical pharmacokinetics of 3-hydroxy-3-methylglutaryl co-enzyme A (HMG-CoA) reductase inhibitors (statins) and angiotensin II receptor antagonists. The mechanisms of such variability are discussed quantitatively, with building a hypothetical model for pravastatin, and validated against other statins. Our analyses suggest that the ethnic variability in the plasma exposure of statins cannot be explained only by the difference in the allele frequencies of organic anion-transporting polypeptide (OATP)1B1 and breast cancer resistance protein (BCRP), and the intrinsic ethnic variability in the activity of OATP1B1 (the ratio of Japanese/Caucasians is 0.584) must be considered. Further work and validation with additional data will clarify the applicability of this model to other OATP1B1 substrates.

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

AIM

CYP2C9 enzyme metabolizes numerous clinically important drugs. The aim of this study is to investigate the frequencies of CYP2C9 genotypes and the effects of selected alleles on losartan pharmacokinetics in a large sample of the Korean population.

METHODS

The CYP2C9 gene was genotyped in 1796 healthy Korean subjects. CYP2C9 alleles (CYP2C9*1, *2, *3 and *13 alleles) were measured using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay and direct sequencing assay. The enzymatic activity of each CYP2C9 genotype was evaluated using losartan as the substrate.

RESULTS

The frequencies of CYP2C9*1, *3 and *13 allele were 0.952 (95% confidence interval 0.945-0.959), 0.044 (95% CI 0.037-0.051) and 0.005 (95% CI 0.003-0.007), respectively. The frequencies of the CYP2C9*1/*1, *1/*3, *1/*13 and *3/*3 genotypes were 0.904 (95% CI 0.890-0.918), 0.085 (95% CI 0.072-0.098), 0.009 (95% CI 0.005-0.013) and 0.001 (95% CI 0.000-0.002), respectively. In the pharmacokinetics studies, the AUC(0-∞) of losartan in CYP2C9*3/*3 subjects was 1.42-fold larger than that in CYP2C9*1/*1 subjects, and the AUC(0-∞) of E-3174, a more active metabolite of losartan, in CYP2C9*3/*3 subjects was only 12% of that in CYP2C9*1/*1 subjects.

CONCLUSION

The results confirmed the frequencies of CYP2C9 genotypes in a large cohort of Koreans, and detected the CYP2C9*3/*3 genotype. CYP2C9*3/*3 subjects metabolized much less losartan into E-3174 than CYP2C9*1/*1 subjects.

Repeated administration of berberine inhibits cytochromes P450 in humans

PURPOSE

Berberine is a plant alkaloid that is widely used to treat gastrointestinal infections, diabetes, hypertension, and hypercholesterolemia. Many studies have reported interactions between berberine-containing products and cytochromes P450 (CYPs), but little is known about whether berberine alters CYP activities in humans, especially after repeated doses.

METHODS

A two-phase randomized-crossover clinical study in healthy male subjects was performed. After 2 weeks of berberine (300 mg, t.i.d., p.o.) administration, midazolam, omeprazole, dextromethorphan, losartan, and caffeine were used to evaluate enzyme activities of CYP3A4, 2C19, 2D6, 2C9, and CYP1A2, respectively.

RESULTS

A decrease in CYP2D6 activity was observed as the 0-8 h urinary dextromethorphan/dextrorphan increased ninefold (P < 0.01). In addition, losartan/E-3174 ratio doubled (P < 0.01) after BBR administration, indicating a decrease in CYP2C9 activity. CYP3A4 activity was also inhibited, as the C(max), AUC(0-∞), and AUC(0-12) of midazolam were increased 38% (P < 0.05), 40% (P < 0.01), and 37% (P < 0.05) after BBR treatment, respectively. Compared with the placebo period, the T(max) and T(1/2) of midazolam during BBR administration were prolonged from 3.03 ± 0.27 to 3.66 ± 0.37 h and 0.66 ± 0.08 to 0.99 ± 0.09 h, respectively; the oral clearance of midazolam was decreased 27% (P < 0.05); and the phenotypic indices of 1 h midazolam/1'-hydroxymidazolam increased 59% (P < 0.01). There were no statistically significant differences in the pharmacokinetic parameters of the other probe drugs between placebo and the BBR-treated group.

CONCLUSIONS

Repeated administration of berberine (300 mg, t.i.d., p.o.) decreased CYP2D6, 2C9, and CYP3A4 activities. Drug-drug interactions should be considered when berberine is administered.

Low dose requirement for warfarin treatment in a patient with CYP2C9*3/*13 genotype

BACKGROUND

Cytochrome P450 2C9 (CYP2C9) is the major isoform of the CYP2C subfamily, and is involved in the metabolism of many clinically important therapeutic agents. Here we describe a patient who was intolerant of warfarin treatment because of impaired drug metabolism related to the CYP2C9*3/*13 genotype and high warfarin sensitivity associated with the VKORC1 1173TT genotype.

CASE

A 64-year-old Korean man had taken warfarin for treatment of an occluded left subclavian artery and atrial fibrillation. Although the warfarin doses prescribed were not high (14 mg/week) during the induction of anticoagulation, the prothrombin time (PT) was elevated to over 120 s after two weeks of warfarin therapy. For this patient, a very low dose of warfarin (4 mg/week) was required in order to achieve target INR values.

CONCLUSIONS

To the best of our knowledge, this is the first report of a patient with CYP2C9*3/*13 and VKORC1 1173TT genotypes who had slower than normal warfarin metabolism, resulting in the need to administer an extremely low dose of warfarin in order to achieve the target INR value. Our report reinforces the relevance of pharmacogenetic testing to explain warfarin dose variability and to enable individualized dosage adjustments for improved warfarin treatment outcomes.

Effects of CYP2C9*1/*13 on the pharmacokinetics and pharmacodynamics of meloxicam

AIMS

To determine the effects of the CYP2C9*1/*13 genotype on the pharmacokinetics and pharmacodynamics of meloxicam in Korean subjects.

METHODS

Meloxicam (15 mg) was orally administered to 21 healthy Korean volunteers with either the CYP2C9*1/*1 or the CYP2C9*1/*13 genotype. Plasma meloxicam concentrations were analysed by HPLC-UV for 72 h after drug administration. The pharmacodynamic effects of meloxicam were determined by measuring TXB(2) generated in blood.

RESULTS

The AUC(0,∞) and C(max) of meloxicam were 2.43- and 1.46-fold higher in the CYP2C9*1/*13 group than in the CYP2C9*1/*1 group, respectively. The oral clearance of meloxicam was significantly lower in the CYP2C9*1/*13 group (37.9% of wild type) than in the CYP2C9*1/*1 group. The t(1/2) of meloxicam was 1.84-fold longer in the CYP2C9*1/*13 group than in the CYP2C9*1/*1 group. The rate of TXB(2) production was significantly lower in the CYP2C9*1/*13 group than in the CYP2C9*1/*1 group.

CONCLUSIONS

The CYP2C9*1/*13 genotype is associated with decreased metabolism and increased pharmacodynamic effects of meloxicam.

Pharmacokinetic evaluation of losartan

INTRODUCTION

Blockade of the renin-angiotensin system is one of the major therapeutic strategies in the management of patients with essential hypertension, congestive heart failure and diabetic as well as non-diabetic renal diseases. As the first angiotensin II receptor blocker (ARB) on the market, losartan belongs to the most frequently prescribed ARB.

AREA COVERED

The present review examines the pharmacokinetics of losartan with a special discussion on the dose of losartan that should be used in clinical practice to obtain the maximal benefits of the drug. Readers are provided with arguments suggesting that the dose of 50 mg losartan is probably too low and that losartan should preferably be prescribed at the dose of 100 mg/day or higher.

EXPERT OPINION

Losartan is an effective antagonist of angiotensin II AT(1) receptors which has been shown to provide important clinical benefits in patients with hypertension, congestive heart failure and renal diseases. Losartan should be prescribed at the dose of 100 mg/day and the use of higher doses should be reconsidered in future studies to improve its clinical efficacy.