<Emphasis Type="Italic">CYP3A5 *1</Emphasis> allele associated with tacrolimus trough concentrations but not subclinical acute rejection or chronic allograft nephropathy in Japanese renal transplant recipients

Purpose  We assessed reported associations of CYP3A5 *1 allele with a delay in achieving target tacrolimus concentrations, and occurrence of biopsy-confirmed subclinical acute rejection (SAR) and chronic allograft nephropathy (CAN) in Japanese subjects. Methods  Forty-one renal allograft recipients were studied. The targeted tacrolimus trough concentrations were 20–25 ng/mL up to 2 weeks post-transplantation, 10–15 ng/mL up to 6 weeks, and 5–10 ng/mL thereafter. At 1 month and 1 year post-transplantation, allograft biopsies were performed. Results  The CYP3A5 *1/*1 + *1/*3 (expresser) and *3/*3 (nonexpresser) alleles were detected in 19 and 22 patients, respectively. Although the mean trough concentrations were lower in CYP3A5 expressers than nonexpressers for the first 3 weeks, no difference in frequency of SAR among CYP3A5 genotypes was found. The mean trough concentrations were lower from 8 to 12 months post-transplantation, and the frequency of CAN was lower in CYP3A5 expressers. Conclusions  In contrast to the previous reports, the CYP3A5 *1 allele was not associated with the frequency of SAR or CAN, suggesting that further studies of different immunosuppressive strategies using tacrolimus are needed to confirm the adequate dosing and concentration of tacrolimus for each CYP3A5 genotype.     

肾移植病人西罗莫司血药浓度/剂量比与CYP3A5基因多态性的关系

目的:研究肾移植术后病人CYP3A5基因多态性与免疫抑制剂西罗莫司临床个体化给药剂量的关系。方法:采用聚合酶链反应(PCR)和限制性内切片段多态性(RFLP)的方法对105例健康受试者和50例肾移植术后病人进行CYP3A5基因分型。使用高效液相色谱(HPLC)测定病人的西罗莫司血药浓度。比较不同基因型之间的西罗莫司的血药浓度与每千克体重的剂量(C/D)比值的差异。结果:健康受试者和肾移植病人的CYP3A5 A6986G SNPs,CYP3A5*3的发生频率分别为72.9％和71％,差异无显著意义(P>0.05)。肾移植*1/*3型病人的C/D比值(362±s108)μg·L~(-1)per mg·kg~(-1)和*3/*3型病人的C/D比值(375±123)μg·L~(-1)per mg·kg~(-1)差异无显著意义(P>0.05),但两者C/D值均明显高于*1/*1型病人(199±65)μxg·L~(-1)per mg·kg~(-1),差异具有显著意义(P<0.05)。结论:肾移植病人的CYP3A5基因多态性与西罗莫司血药浓度具有相关性,*1/*3型和*3/*3型病人拟取得相似的血药浓度要比*1/*1型病人服用更低剂量的西罗莫司。研究肾移植病人的CYP3A5基因型,有利于肾移植病人术后西罗莫司个体化用药方案的制定。     

Effect of polymorphic CYP3A5 genotype on the single-dose simvastatin pharmacokinetics in healthy subjects

Simvastatin, a cholesterol-lowering agent, is mainly metabolized by CYP3A4/5. The objective of this study was to investigate the effect of CYP3A5*3 genotype on the pharmacokinetics of simvastatin in humans. Twenty-two men with CYP3A5*1/*1 (n = 4), CYP3A5*1/*3 (n = 8), or CYP3A5*3/*3 (n = 10) genotypes were enrolled. Each subject ingested a 20-mg dose of simvastatin, and plasma simvastatin concentrations were measured for 12 hours after dosing. The mean (+/-SD) area under the plasma concentration-time curve for simvastatin in the CYP3A5*1/*1 carriers (4.94 +/- 2.25 ng x h/mL) was significantly lower than CYP3A5*3/*3 carriers (16.35 +/- 6.37 ng x h/mL; P = .013, Bonferroni test). The mean (+/-SD) oral clearance was also significantly different between CYP3A5*1/*1 carriers (4.80 +/- 2.35 L/h) and CYP3A5*3/*3 carriers (1.35 +/- 0.61 L/h; P < .05, Dunn's test). However, other pharmacokinetic parameters including peak plasma concentrations and half-life did not show any difference between genotype groups. These findings suggest that the polymorphic CYP3A5 gene affects the disposition of simvastatin and provides a plausible explanation for interindividual variability of simvastatin disposition.     

Differences in flurbiprofen pharmacokinetics between CYP2C9*1/*1, *1/*2, and *1/*3 genotypes

OBJECTIVE: This study was conducted to examine differences in flurbiprofen metabolism among individuals with the CYP2C9*1/*1, *1/*2, and *1/*3 genotypes. METHODS: Fifteen individuals with the CYP2C9*1/*1 ( n=5), *1/*2 ( n=5), and *1/*3 ( n=5) genotypes received a single 50-mg oral dose of flurbiprofen. Plasma and urine samples were collected over 24 h, and flurbiprofen and 4'-hydroxyflurbiprofen pharmacokinetic data were compared across genotypes. RESULTS: CYP2C9 genotype was a significant predictor of flurbiprofen metabolism and accounted for 59% of the variability in flurbiprofen AUC(0- infinity ), and approximately 50% of the variability in flurbiprofen oral clearance, formation clearance to 4'-hydroxyflurbiprofen, and the 0 to 24-h urinary metabolic ratio of flurbiprofen to 4'-hydroxyflurbiprofen. Flurbiprofen AUC(0- infinity )was significantly higher and all measures of flurbiprofen clearance were significantly lower in the CYP2C9*1/*3 individuals than in those with *1/*1. Significant differences in these parameters were not detected between *1/*2 subjects and *1/*1 subjects. CONCLUSIONS: CYP2C9 genotype is a significant predictor of flurbiprofen disposition in humans by altering CYP2C9-mediated metabolism and reducing systemic clearance. The effects are most pronounced in individuals carrying the *3 allele.     

Multiple regression analysis of pharmacogenetic variability of carvedilol disposition in 54 healthy Japanese volunteers

The aim of this study was to evaluate the pharmacogenetic variability in the disposition of carvedilol in the Japanese population. Five or 10 mg of carvedilol was orally administered to 54 healthy Japanese subjects (22-44 years old), and blood samples were taken at 2 and 6 h after dosing. We determined the polymorphic alleles of CYP2D6, CYP2C9, CYP2C19, CYP3A5, UGT2B7, and MDR1 in each subject. The whole blood concentration of R- and S-carvedilol was measured by an HPLC method. The pharmacokinetic parameters in individual subjects were estimated by the Bayesian method using the nonlinear mixed effects model (NONMEM) program. We then examined the effect of the genetic polymorphisms on the variability in the pharmacokinetics of carvedilol using a multiple regression analysis. The oral clearance (CL/F) and also apparent volume of distribution (V/F) of both enantiomers were significantly lower in the subjects with the CYP2D6*10 allele than those with the CYP2D6*1/*1, *1/*2, or *2/*2 genotype, confirming our previous finding that the bioavailability (F) and systemic clearance (CL) of R- and S-carvedilol in the liver is significantly altered in Japanese with the CYP2D6*10 allele. On the other hand, CYP2C9*3, CYP2C19*2, CYP2C19*3, CYP3A5*3, UGT2B7*2, and MDR1 C3435T did not significantly affect the pharmacokinetics of carvedilol in Japanese subjects.     

Losartan and E3174 pharmacokinetics in cytochrome P450 2C9*1/*1, *1/*2, and *1/*3 individuals

STUDY OBJECTIVE: To determine if differences in the pharmacokinetics of losartan and its pharmacologically active E3174 metabolite exist among individuals expressing the cytochrome P450 (CYP) 2C9*1/*1, *1/*2, and *1/*3 genotypes. DESIGN: Single-dose pharmacokinetic study. SETTING: University general clinical research center. SUBJECTS: Fifteen healthy volunteers, five from each genotype: CYP2C9*1/*1, *1/*2, and *1/*3. INTERVENTION: A single oral dose of losartan 50 mg. MEASUREMENTS AND MAIN RESULTS: Plasma and urine samples were collected for 24 hours, and losartan and E3174 pharmacokinetic data were compared across the three genotypes. Orthostatic blood pressure was measured over 12 hours after dosing. No significant differences were observed among the three groups in losartan or E3174 area under the plasma concentration-time curve, losartan or E3174 elimination half-life, or losartan oral clearance. A significant association between CYP2C9 genotype and losartan to E3174 formation clearance was observed, such that 50% of the variability was accounted for by the genotype. No significant relationship between that genotype and blood pressure was observed at any time. CONCLUSION: Differences in the pharmacokinetics of losartan and its active E3174 metabolite were not observed in healthy subjects with the genotype of CYP2C9*1/*2 and *1/*3 compared with those expressing *1/*1. Alterations in losartan dosing in CYP2C9*1/*2 and *1/*3 individuals does not appear necessary.     

Benzbromarone pharmacokinetics and pharmacodynamics in different cytochrome P450 2C9 genotypes

Benzbromarone is a uricosuric drug and has been shown to be metabolized predominantly by cytochrome P450(CYP)2C9 in vitro findings. This study aims to investigate the influence of the CYP2C9 genotype on plasma levels of benzbromarone and 6-hydroxybenzbromarone, as well as uric acid lowering effects. A single oral dose pharmacokinetic and pharmacodynamic trial of benzbromarone (100 mg) was performed in 20 healthy volunteers, which included 15 with CYP2C9*1/*1, 4 with CYP2C9*1/*3, and 1 with CYP2C9*3/*3. The oral clearance of benzbromarone in the CYP2C9*1/*1 genotype and CYP2C9*1/*3 genotype was 58.8±25.2 L/hr/kg (mean±SD) and 51.3±7.9 L/hr/kg, respectively, whereas 8.58 L/hr/kg in the CYP2C9*3/*3 genotype. The metabolic ratio (6-hydroxybenzbromarone/benzbromarone) in urine was 38.6±10.7 in the CYP2C9*1/*1 genotype, 35.4±12.4 in the CYP2C9*1/*3 genotype and 12.9 in the CYP2C9*3/*3 genotype. Although benzbromarone significantly increased the urinary excretion and reduced the plasma concentration of uric acid, there were no significant differences in its effects for different CYP2C9 genotypes. These results suggest a critical role for CYP2C9 in the metabolism of benzbromarone in humans and a possible risk of toxicity in the CYP2C9*3 homozygote by lowering clearance of the drug. Further studies are required to assess the clinical impact of CYP2C9 on the metabolism of benzbromarone.     

肾移植受者CYP3A5基因多态性对他可莫司代谢的影响

目的研究CYP3A基因多态性对肾移植受者他可莫司代谢的影响。方法50例肾移植受者采用FK506＋霉酚酸酯＋强的松三联免疫抑制方案,FK506起始剂量0．15mg／（kg·d）,1w后根据目标血药浓度调整。CYP3A5基因多态性检测采用聚合酶链反应-限制性片段长度多态性（PCR—RFLP）方法,50例肾移植受者分为＊1／＊1型（12例）、＊1／＊3型（16例）、＊3／＊3型（22例）共3组。比较6个月内FK506的血药浓度／剂量比。结果 肾移植术后7天、1月、3月、6月＊3／＊3型患者FK506的血药浓度／剂量比显著高于＊1／＊1型和＊1／＊3型（P〈0．05）。结论由于CYP3A5基因多态性影响,＊1／＊1型组的患者早期难以达到有效FK506目标血药浓度,应该提高该组患者的起始用药剂量,根据CYP3A5基因多态性作为FK506个体化用药的依据,可以减少早期急性排斥反应,提高肾移植的临床效果。     

Minimal effect of MDR1 and CYP3A5 genetic polymorphisms on the pharmacokinetics of indinavir in HIV-infected patients

AIMS: The protease inhibitor indinavir is characterized by an important interindividual pharmacokinetic variability, which results from the actions of the metabolizing enzymes cytochrome P450 (CYP) 3A and the multidrug efflux pump P-glycoprotein (P-gp), encoded by MDR1. Using a population pharmacokinetic approach, we investigated the effect of several MDR1 and CYP3A5 polymorphisms on the pharmacokinetic parameters of indinavir in HIV-infected patients. METHODS: Twenty-eight patients receiving indinavir alone or together with ritonavir were included. Indinavir pharmacokinetics were studied over a 12 h interval. Genetic polymorphisms were assessed by real-time PCR assays and direct sequencing for MDR1 and by PCR-SSCP analysis for CYP3A5. RESULTS: The pharmacokinetics of indinavir were best described by a one-compartment model with first-order absorption. In the final model, the MDR1 C3435T genotype and ritonavir were identified as statistically significant covariates (P 相似文献   

Effects of the CYP2C9*1/*13 genotype on the pharmacokinetics of lornoxicam

Lornoxicam is extensively metabolized by CYP2C9, and a CYP2C9*13 is one of the principal variant alleles in East Asian populations. The aim of this study was to evaluate the effects of CYP2C9*1/*13 on the pharmacokinetic parameters of lornoxicam in healthy individuals. A single oral dose of 8 mg lornoxicam was given to 22 Korean volunteers with different CYP2C9 genotypes (8, 8 and 6 carriers of CYP2C9*1/*1, *1/*3 and *1/*13 genotypes, respectively). Lornoxicam and 5'-hydroxylornoxicam levels were analysed using HPLC-UV in plasma samples collected up to 24 hr after taking the drug. In individuals with CYP2C9*1/*13, lornoxicam had a higher C(max) (p < 0.001), a longer half-life (p < 0.001), a lower oral clearance (p < 0.001) and a higher area under the plasma concentration-time curve from zero to infinity (AUC(inf) ) than in CYP2C9*1/*1 individuals (p < 0.001). The C(max) and AUC(inf) of 5'-hydroxylornoxicam were lower in CYP2C9*1/*13 individuals than in CYP2C9*1/*1 individuals, but the half-life of 5'-hydroxylornoxicam did not differ between the two groups. The half-life, oral clearance and AUC(inf) of lornoxicam were similar in individuals with CYP2C9*1/*13 and those with CYP2C9*1/*3. The C(max) , half-life and AUC(inf) of 5'-hydroxylornoxicam were also similar in both groups, although C(max) was higher in CYP2C9*1/*13 individuals (p < 0.01). A CYP2C9*1/*13 genotype markedly reduced the conversion of lornoxicam to 5'-hydroxylornoxicam, to a similar extent as that observed with the CYP2C9*1/*3 genotype.     

肾移植患者西罗莫司的群体药动学研究

目的:建立中国肾移植患者西罗莫司的群体药动学模型,为实施个体化用药提供理论支持。方法:选择47名肾移植术后采用西罗莫司+泼尼松+环孢素或他克莫司或霉酚酸酯(MMF)三联免疫抑制治疗的患者为研究对象,回顾性收集47名患者服药后的101个西罗莫司稳态血药浓度及相应的试验室检查数据,运用Winnonmix药动学软件,采用非线性混合效应模型(NONMEM)分析体重、年龄、性别、给药剂量、合并用药、肌酐清除率等对药动学参数的影响。最终模型的验证采用Jackknife法进行内部验证。结果:西罗莫司符合无滞后时间的一级消除动力学一室模型。固定效应结果量子,合用MMF和体重可影响药物清除率。最终模型公式为:CL/F(L·h-1)=11.01×0.14MMF+0.089×W。CL/F和Vd/F的群体典型值分别是11.01L·h-1和3616L,个体间变异分别为62.82%和85.07%。观测值和预测值间的残差(SD)和相关系数(r)分别是1.0ng·mL-1和0.94。结论:所建立的群体药动学模型能较好地估算服用西罗莫司的肾移植患者的个体及群体药动学参数,对指导临床个体化用药具有重要意义。     

CYP3A5 genotype is not associated with a higher risk of acute rejection in tacrolimus-treated renal transplant recipients

OBJECTIVE: Patients expressing the tacrolimus-metabolizing enzyme, cytochrome P450 (CYP) 3A5, require more tacrolimus to reach target concentrations. We studied the influence of the CYP3A5(*)3 allele, which results in the absence of CYP3A5 protein, on tacrolimus dose and exposure, as well as the incidence of biopsy-proven acute rejection (BPAR) after renal transplantation. METHODS: A total of 136 patients participating in a prospective, randomized-controlled clinical trial with the primary aim of comparing the efficacy of a fixed-dose versus a concentration-controlled mycophenolate mofetil immunosuppressive regimen, were genotyped for CYP3A5(*)3. The patients described herein, participated in a pharmacogenetic substudy and were all treated with mycophenolate mofetil, corticosteroids and tacrolimus. Tacrolimus predose concentrations (C(0)) were measured on day 3 and 10, and month 1, 3, 6 and 12. RESULTS: Compared with CYP3A5(*)3/(*)3 individuals (n=110), patients carrying at least one CYP3A5(*)1 (wild-type) allele (CYP3A5 expressers; n=26) had a lower tacrolimus C(0) on day 3 only (16.6 versus 12.3 ng/ml, respectively), whereas dose-corrected tacrolimus C(0) were significantly lower in the latter group at all time points. After day 3, the overall daily tacrolimus dose was 68% higher in CYP3A5 expressers (P<0.001). The incidence of BPAR was comparable between CYP3A5 expressers and nonexpressers (8 versus 16%, respectively; P=0.36). CONCLUSION: We conclude that patients expressing CYP3A5 need more tacrolimus to reach target concentrations and have a lower tacrolimus exposure shortly after transplantation. This delay in reaching target concentrations, however, did not result in an increased incidence of early BPAR and therefore, genotyping for CYP3A5 is unlikely to improve short-term transplantation outcome.     

Influence of the CYP3A5 and MDR1 genetic polymorphisms on the pharmacokinetics of tacrolimus in healthy Korean subjects

AIMS: To determine the frequencies of the genotypes of CYP3A5 and MDR1 and to examine the influence of the polymorphisms of these genes on tacrolimus pharmacokinetics in the Korean population. METHODS: Twenty-nine healthy Koreans who participated in the previous tacrolimus pharmacokinetic study were genotyped for CYP3A4*1B, CYP3A5*3, MDR1 c.1236C-->T, MDR1 c.2677G-->A/T and MDR1 c.3435C-->T. The relationship between the genotypes so obtained and tacrolimus pharmacokinetics observed in the previous study was examined. RESULTS: No subject in this study had the CYP3A4*1B variant. The observed frequencies of CYP3A5*1/*1, *1/*3, and *3/*3 were 0.069 [confidence interval (CI) -0.023, 0.161], 0.483 (CI 0.301, 0.665) and 0.448 (CI 0.267, 0.629), respectively. AUC(0-infinity) for the CYP3A5*1/*1 or *1/*3 genotype was 131.5 +/- 44.8 ng h ml(-1) (CI 109.6, 153.5), which was much lower compared with the CYP3A5*3/*3 genotype of 323.8 +/- 129.3 ng h ml(-1) (CI 253.5, 394.1) (P = 2.063E-07). Similarly, C(max) for the CYP3A5*1/*1 or *1/*3 genotype was 11.8 +/- 3.4 ng ml(-1) (CI 10.1, 13.5), which was also much lower compared with the CYP3A5*3/*3 genotype of 24.4 +/- 12.3 ng ml(-1) (CI 17.8, 31.1) (P = 0.0001). However, there was no significant difference in tacrolimus pharmacokinetics among the MDR1 diplotypes of CGC-CGC, CGC-TTT, CGC-TGC, TTT-TGC or TTT-TTT (P = 0.2486). CONCLUSIONS: This study shows that the CYP3A5*3 genetic polymorphisms may be associated with the individual difference in tacrolimus pharmacokinetics. An individualized dosage regimen design incorporating such genetic information would help increase clinical efficacy of the drug while reducing adverse drug reactions.     

Effect of CYP3A4 genetic polymorphisms on pharmacokinetics of tinidazole

In the present study, we aimed to investigate the frequency of CYP3A4*18B genetic polymorphism in Han Chinese populations, and to assess the effect of the CYP3A4*18B genetic polymorphism on the pharmacokinetics of tinidazole. A total of 100 healthy volunteers from Han nationalities in China were recruited. DNA was extracted from peripheral leukocytes using a standard protocol. A PCR-RFLP method was developed to detect the alleles of CYP3A4*18B. A pharmacokinetic study of tinidazole was then carried out in two groups with CYP3A4*1/*1 (n = 10) and CYP3A4*1/*18B (n = 9) genotypes. Concentrations of tinidazole were determined using high-performance liquid chromatography in plasma samples that were collected up to 72 h after drug intake. In this study, 88 healthy volunteers were found with CYP3A4*1/*1 genotype, and 12 were found with CYP3A4*1/*18Bgenotype. CYP3A4*18B/*18B were absent from all subjects. The allele frequencies of CYP3A4*18B were 6%. The pharmacokinetic parameters of CYP3A4*1/*1 genotype and CYP3A4*1/*18B genotype in healthy subjects were as follows: t_1/2: (15.92±1.62), (15.77±1.67) h; C_max: (18.72±3.10), (20.25±3.42) mg/L; t_max: (1.50±0.66), (1.45±0.69) h; V_d/F: (55.73±10.66), (51.30±7.75) L; CL/F: (2.44±0.47), (2.26±0.30) L·h; AUC_0–∞: (424.40±82.38), (450.53±69.48) mg·h/L. Collectively, the CYP3A4*18B genetic polymorphism did not affect pharmacokinetics of tinidazolein healthy volunteers.     

Nonlinear mixed effects model analysis of the pharmacokinetics of aripiprazole in healthy Japanese males

The population pharmacokinetic parameters of aripiprazole in healthy Japanese males were estimated using a nonlinear mixed effects model (NONMEM) program. Pharmacokinetic data for population analysis were obtained from the single-dose (24 subjects), multiple-dose (15 subjects), and itraconazole-coadministration (27 subjects) trials. The time course of plasma aripiprazole concentration following oral administration was well described by a two-compartment model with first-order input. The mean values of the absorption lag time (ALAG) and absorption rate constant (KA) were estimated to be 0.805 h and 2.65 h(-1), respectively. The mean volume of the central (V(1)/F) and peripheral (V(2)/F) compartment was 3.84 and 1.54 l/kg, respectively, and the mean value of inter-compartment clearance (Q/F) was 0.168 l/h/kg. Oral clearance (CL/F) was estimated to be 0.0645 l/h/kg in the group with CYP2D6*1/*1, *1/*2 and *2/*2. The decrease in CL/F was estimated to be 0.0135 l/h/kg in the group with CYP2D6*1/*5, *1/*10, *2/*5, *2/*10, and *2/*41, and 0.0293 l/h/kg in the group with CYP2D6*5/*10, *10/*10, and *41/*41. The plasma concentration of aripiprazole was increased by coadministration of itraconazole, and the decrease in CL/F was estimated to be 0.0181 l/h/kg.     

Influence of CYP2C9 and CYP2D6 polymorphisms on the pharmacokinetics of nateglinide in genotyped healthy volunteers

BACKGROUND: The oral hypoglycaemic drug nateglinide is eliminated from the human body via hepatic biotransformation and renal tubular secretion. According to in vitro data, about 70% of nateglinide intrinsic clearance may be mediated by cytochrome P450 (CYP) 2C9 and a smaller fraction by CYP3A4 and CYP2D6. OBJECTIVE: To assess the impact of CYP2C9 polymorphisms and of the CYP2D6 poor metaboliser genotype on the pharmacokinetics of nateglinide and its effects on insulin, glucose and glucagon in plasma. DESIGN AND PARTICIPANTS: A prospective clinical study in 26 healthy volunteers chosen for their CYP2C9 and CYP2D6 genotype was conducted with individuals carrying wild-type genotype as reference group. METHODS: Serial plasma nateglinide, glucose, insulin and glucagon concentrations were measured over 34 hours after a 180 mg dose of nateglinide under challenge with 75 g of oral glucose at 0, 4 and 8 hours after nateglinide intake. Kinetics were evaluated by nonparametric methods and by population pharmacokinetic-pharmacodynamic modelling. RESULTS: Significantly reduced oral nateglinide clearance was found in carriers of CYP2C9*3 alleles, (p < 0.01), whereas carriers of CYP2C9*2 alleles had kinetic parameters similar to those of carriers of the wild-type allele (p = nonsignificant). Median total clearances were 7.9, 8.4, 6.5, 6.9, 5.8 and 4.1 L/h in carriers of the CYP2C9 genotypes *1/*1, *1/*2, *2/*2, *1/*3, *2/*3 and *3/*3. Median clearance in three carriers of two deficient CYP2D6 alleles was 9.4 L/h. These differences in nateglinide kinetics due to CYP2C9 genotypes did not result in statistically significant differences in plasma glucose, insulin and glucagon. Pharmacokinetic-pharmacodynamic modelling revealed a minor effect of CYP2C9 genotype on insulin and glucose, and extrapolations indicated that carriers of the CYP2C9*3/*3 genotype may be at a slightly higher risk of hypoglycaemia compared with carriers of CYP2C9*1, particularly when taking nateglinide doses above 120 mg. CONCLUSION: The effect of CYP2C9 polymorphisms on nateglinide kinetics may cause a slightly increased risk for hypoglycaemia, which may become relevant in diabetic patients.     

Catalytic roles of CYP2C9 and its variants (CYP2C9*2 and CYP2C9*3) in lornoxicam 5'-hydroxylation.

The effects of allelic variants of CYP2C9 (CYP2C9*2 and CYP2C9*3) on lornoxicam 5'-hydroxylation were studied using the corresponding variant protein expressed in baculovirus-infected insect cells and human liver microsomes of known genotypes of CYP2C9. The results of the baculovirus expression system showed that CYP2C9.3 gives higher K(m) and lower V(max) values for lornoxicam 5'-hydroxylation than does CYP2C9.1. In contrast, K(m) and V(max) values of CYP2C9.1 and CYP2C9.2 for the reaction were comparable. Lornoxicam 5'-hydroxylation was also determined in liver microsomes of 12 humans genotyped for the CYP2C9 gene (*1/*1, n = 7; *1/*2, n = 2; *1/*3, n = 2; *3/*3, n = 1). A sample genotyped as *3/*3 exhibited 8- to 50-fold lower intrinsic clearance for lornoxicam 5'-hydroxylation than did samples genotyped as *1/*1. However, the values for intrinsic clearance for *1/*3 were within the range of values exhibited by samples of *1/*1. In addition, no appreciable differences were observed in kinetic parameters for lornoxicam 5'-hydroxylation between *1/*1 and *1/*2. In conclusion, this study showed that lornoxicam 5'-hydroxylation via CYP2C9 was markedly decreased by the substitution of Ile359Leu (CYP2C9.3), whereas the effect of the substitution of Arg144Cys (CYP2C9.2) was nonexistent or negligible. Additional in vivo studies are required to confirm that individuals with homologous CYP2C9*3 allele exhibit impaired lornoxicam clearance.     

Population pharmacokinetic and pharmacogenetic analysis of tacrolimus in paediatric liver transplant patients

Aims

To build a population pharmacokinetic model that describes the apparent clearance of tacrolimus and the potential demographic, clinical and genetically controlled factors that could lead to inter-patient pharmacokinetic variability within children following liver transplantation.

Methods

The present study retrospectively examined tacrolimus whole blood pre-dose concentrations (n = 628) of 43 children during their first year post-liver transplantation. Population pharmacokinetic analysis was performed using the non-linear mixed effects modelling program (nonmem) to determine the population mean parameter estimate of clearance and influential covariates.

Results

The final model identified time post-transplantation and CYP3A5*1 allele as influential covariates on tacrolimus apparent clearance according to the following equation:where TVCL is the typical value for apparent clearance, TPT is time post-transplantation in days and the CYP3A5 is 1 where *1 allele is present and 0 otherwise. The population estimate and inter-individual variability (%CV) of tacrolimus apparent clearance were found to be 0.977 l h⁻¹ kg⁻¹ (95% CI 0.958, 0.996) and 40.0%, respectively, while the residual variability between the observed and predicted concentrations was 35.4%.

Conclusion

Tacrolimus apparent clearance was influenced by time post-transplantation and CYP3A5 genotypes. The results of this study, once confirmed by a large scale prospective study, can be used in conjunction with therapeutic drug monitoring to recommend tacrolimus dose adjustments that take into account not only body weight but also genetic and time-related changes in tacrolimus clearance.     

Population estimation of the effects of cytochrome P450 2C9 and 2C19 polymorphisms on phenobarbital clearance in Japanese

A nonlinear mixed-effect modeling (NONMEM) program was used to evaluate the effects of cytochrome P450 (CYP) 2C9 and CYP2C19 polymorphisms on the phenobarbital (PB) population clearance for Japanese epileptics. The pharmacokinetics of the 260 PB concentrations at a steady-state obtained from 79 patients was described with a one-compartment open pharmacokinetic model with first-order elimination. The covariates screened included the total body weight (BW), age, gender, PB daily dose, CYP2C9 and CYP2C19 genotypes, the coadministered antiepileptic drugs (AEDs), and complications. The final model of PB apparent clearance was as follows: CL = 0.23 x (BW/40)0.21 x 0.52CYP2C9*1/*3 x 0.68VPA x 0.85PHT x 0.85SMID x (1 + etaCL) where CL = the clearance of PB; CYP2C9*1/*3 = 1, otherwise 0; VPA = 1 if valproic acid is coadministered, otherwise 0; PHT = 1 if phenytoin is coadministered, otherwise 0; SMID = 1 if complications of severe or profound mental retardation with a significant behavior impairment are presented, otherwise 0; and etaCL = the independent random error distributed normally with the mean zero and variance equal to omegaP2. The total clearance of PB decreased by 48% in patients with CYP2C9*1/*3 genotype in comparison with those with CYP2C9*1/*1 genotype (P < 0.001). An effect of CYP2C19 polymorphisms was not detected. To our knowledge, this is the first report to demonstrate that the CYP2C9 genotype affects the PB metabolism in routine care, but the results should be further verified in other ethnic populations.