Genetic polymorphisms of the CYP3A4, CYP3A5, and MDR-1 genes and pharmacokinetics of the calcineurin inhibitors cyclosporine and tacrolimus

BACKGROUND: The calcineurin inhibitors cyclosporine (INN, cyclosporin) and tacrolimus have a narrow therapeutic index and show considerable interindividual variability in their pharmacokinetics. The low oral bioavailability of calcineurin inhibitors is thought to result from the actions of the metabolizing enzymes cytochrome P450 (CYP) 3A4 and CYP3A5 and the multidrug efflux pump P-glycoprotein, encoded by MDR-1. OBJECTIVE: Our objective was to determine the role of genetic polymorphisms in CYP3A4, CYP3A5, and MDR-1 with respect to interindividual variability in cyclosporine and tacrolimus pharmacokinetics. METHODS: Kidney transplant recipients receiving cyclosporine (n = 110) or tacrolimus (n = 64) were genotyped for CYP3A4*1B and *3, CYP3A5*3 and *6, and MDR-1 C3435T. Dose-adjusted trough levels were determined and correlated with the corresponding genotype. RESULTS: Tacrolimus dose-adjusted trough levels were higher in CYP3A5*3/*3 patients (n = 45) than in *1/*3 plus *1/*1 patients (n = 17), as follows: median and range, 94 (34-398) ng/mL per mg/kg versus 61 (37-163) ng/mL per mg/kg (P <.0001, Mann-Whitney test). CYP3A4*1B allele carriers (n = 10) had lower tacrolimus dose-adjusted trough levels compared with those in patients with the wild-type (*1/*1) genotype (n = 54): median and range, 57 (40-163) ng/mL per mg/kg versus 89 (34-398) ng/mL per mg/kg) (P =.003, Mann-Whitney test). No evidence was found supporting a role for the MDR-1 C3435T polymorphism in tacrolimus dose requirement. None of the polymorphisms studied correlated with cyclosporine dose-adjusted predose concentrations. CONCLUSION: As a group, patients with the CYP3A5*3/*3 genotype require less tacrolimus to reach target predose concentrations compared with CYP3A5*1 allele carriers, whereas CYP3A4*1B carriers require more tacrolimus to reach target trough concentrations compared with CYP3A4*1 homozygotes.     

CYP3A5和多重耐药基因1多态性对肾移植患者他克莫司药代动力学参数的影响

目的探讨细胞色素P450,家族3,亚家族A,多肽5(CYP3A5)基因和多重耐药基因1(MDR1)C3435T多态性对肾移植患者他克莫司药代动力学参数的影响,在基因水平为临床合理用药提供参考。方法采用聚合酶链反应(PCR)和限制酶切片长多态性(RFIP)方法对63例肾移植术后患者进行CYP3A5和MDR1基因分型。移植手术1个月后进行血药浓度测定和药代动力学参数计算。结果携带CYP3A5*1基因型肾移植患者的剂量校正曲线下面积(AUC_(0-t))明显低于CYP3A5*3*3型患者,在随后对上述2组不同CYP3A5基因分型的患者进行MDR1的C3435T基因多态性分型研究表明,MDR1 C3435T基因多态性对他可莫司的药代动力学参数无明显影响。结论 CYP3A5基因多态性与他可莫司药代动力学参数相关,携带CYP3A5*1基因型肾移植患者比CYP3A5*3*3型患者需要较高的剂量才能达到目的浓度;而在影响他可莫司药代动力学参数的因素中MDR1 C3435T基因多态性不是重要因素。药代动力学参数的测定有利于器官移植患者剂量选择及个体化用药治疗。     

Effect of CYP3A5*3 genotype on the pharmacokinetics and pharmacodynamics of amlodipine in healthy Korean subjects

BACKGROUND AND OBJECTIVE: 1,4-Dihydropyridine calcium channel blockers, including amlodipine, are mainly metabolized by cytochrome P450 (CYP) 3A. We investigated the effect of CYP3A5*3 genotype on the pharmacokinetics and pharmacodynamics of amlodipine in healthy Korean male subjects. METHODS: Forty healthy male participants were enrolled and genotyped for the CYP3A5*3 gene. Each subject ingested a 5-mg dose of amlodipine, and plasma amlodipine concentrations were measured for 144 hours after dosing. Blood pressure and pulse rate were also measured for pharmacodynamic analysis. RESULTS: Among the 40 volunteers, 24 were CYP3A5*3/*3 carriers and 16 were CYP3A5*1 carriers (CYP3A5*1/*1 in 2 and CYP3A5*1/*3 in 14). The difference in the oral clearance of amlodipine approached statistical significance between the 2 major genotype groups, with CYP3A5*1 carriers (27.0 +/- 8.2 L/h) showing 20% lower clearance than CYP3A5*3/*3 carriers (32.4 +/- 10.2 L/h) (P = .063). However, the mean area under the plasma concentration-time curve of amlodipine was 200.9 +/- 61.9 ng . h/mL for CYP3A5*1 carriers and 167.6 +/- 45.0 ng . h/mL for CYP3A5*3/*3 carriers (P = .029). Moreover, the peak plasma concentration was significantly higher in CYP3A5*1 carriers (3.8 +/- 1.1 ng/mL) than in CYP3A5*3/*3 carriers (3.1 +/- 0.8 ng/mL) (P = .037). Pharmacodynamically, blood pressure and pulse rate were not significantly different between the 2 groups. CONCLUSIONS: CYP3A5*3/*3 carriers exhibited lower plasma amlodipine concentrations than CYP3A5*1 carriers. These findings suggest that the polymorphic CYP3A5 gene affects the disposition of amlodipine and provides a plausible explanation for interindividual variability in amlodipine disposition.     

Influence of CYP2C9 genotypes on the pharmacokinetics and pharmacodynamics of piroxicam

OBJECTIVE: Our objective was to evaluate the influence of cytochrome P450 (CYP) 2C9 polymorphisms on the pharmacokinetics and pharmacodynamics of the nonsteroidal anti-inflammatory drug piroxicam. METHODS: Thirty-five healthy subjects with CYP2C9 genotypes *1/*1 (n=17), *1/*2 (n=9), and *1/*3 (n=9) received a single oral dose of piroxicam (20 mg). Blood samples were collected at various time points up to 240 hours for measurements of the concentrations of piroxicam and thromboxane B2 (TXB2). RESULTS: Piroxicam's area under the plasma concentration-time curve from time 0 to infinity and oral clearance corrected for body weight were 154+/-37 microg.mL-1.h and 2.0+/-0.5 mL.h-1.kg-1, respectively, in CYP2C9*1/*1 individuals, as compared with 256+/-97 mL.h-1 (P=.002) and 1.3+/- 0.4 mL.h-1.kg-1 (P=.002), respectively, in CYP2C9*1/*2 individuals and 259+/- 95 mL.h-1 (P=.002) and 1.3+/- 0.4 mL.h-1.kg-1 (P=.002), respectively, in CYP2C9*1/*3 individuals. There were no significant differences between CYP2C9*1/*2 and CYP2C 9*1/*3 individuals in these pharmacokinetic parameters (P=.95 for area under the plasma concentration-time curve from time 0 to infinity and P=.94 for oral clearance corrected for body weight). The formation of TXB2, reflecting cyclooxygenase type 1 activity, showed significant differences in the area above the effect-time curves (expressed as percent of baseline TXB2.h) between CYP2C9*1/*1 (10,190 +/- 2632) and either CYP2C9*1/*2 (19,255+/-1,291 [P=.00003]) or CYP2C9*1/*3 (18,241+/- 2397 [P=.00003]). The minimum serum TXB2 concentration, however, did not differ among the different genotypes (P=.32, ANOVA). CONCLUSION: Piroxicam's oral clearance was impaired and its inhibitory effect on cyclooxygenase 1 activity was increased in CYP2C9*1/*2 or CYP2C9*1/*3 individuals, as compared with CYP2C 9*1 homozygous individuals.     

Functional impact of CYP2C95, CYP2C96, CYP2C98, and CYP2C911 in vivo among black Africans

Background and aim Previous data indicate that the urinary losartan/E-3174 ratio is a marker for cytochrome P450 (CYP) 2C9 activity in vivo. The functional impact of CYP2C9*5, *6, *8, and *11 polymorphisms in vivo has not been investigated previously in humans. METHODS: A single oral dose of losartan (25 mg) was given to 19 Beninese subjects with CYP2C9*1/*1 (n = 9), *1/*5 (n = 1), *1/*6 (n = 1), *1/*8 (n = 2), *1/*11 (n = 3), *5/*6 (n = 1), *5/*8 (n = 1), and *8/*11 (n = 1) genotypes. Concentrations of losartan and its active metabolite E-3174 were determined in urine from 0 to 8 hours by HPLC. The losartan/E-3174 metabolic ratio was used as a measure of losartan oxidation in vivo. RESULTS: The urinary losartan/E-3174 ratio in the various genotypes was as follows: 1.85 +/- 2.4 (mean +/- SD) for CYP2C9*1/*1, 14.6 for CYP2C9*1/*5, 4.2 for CYP2C9*1/*6, 188 for CYP2C9*5/*6, 11.6 for CYP2C9*5/*8, 0.44 +/- 0.13 (mean +/- SD) for CYP2C9*1/*8, 2.2 for CYP2C9*8/*11, and 5.72 +/- 4.5 (mean +/- SD) for CYP2C9*1/*11. Compared with the CYP2C9*1/*1 genotypes, the losartan/E-3174 ratio was significantly different in the CYP2C9*5 allele carriers (CYP2C9*1/*5, CYP2C9*5/*8, and CYP2C9*5/*6 genotypes) (P =.01, Mann-Whitney) but was not different in CYP2C9*1/*8 (P =.16) and CYP2C9*1/*11 (P =.11) carriers. The urinary losartan/E-3174 ratio of the single CYP2C9*1/*6 subject was higher than the 95% confidence interval of the mean of the CYP2C9*1/*1 group (0.0-3.7), whereas the metabolic ratio of the CYP2C9*8/*11 carrier was inside the 95% confidence interval of the means of the CYP2C9*1/*1 and CYP2C9*1/*11 groups (0.0-18). CONCLUSIONS: The CYP2C9*5 and *6 alleles are associated with decreased enzyme activity in vivo compared with the wild-type variant, whereas the CYP2C9*8 and *11 variants did not appear to have large in vivo effects.     

Acenocoumarol pharmacokinetics in relation to cytochrome P450 2C9 genotype

BACKGROUND AND OBJECTIVES: Cytochrome P450 (CYP) 2C9 is one of the major CYP enzymes involved in the biotransformation of drugs, among others, the oral anticoagulant acenocoumarol. The enzyme has several polymorphisms, with the CYP2C9*2 and CYP2C9*3 variants most commonly present in white patients. Patients with the CYP2C9*3 variant are known to require a lower maintenance dose of racemic acenocoumarol. We investigated the impact of the polymorphisms CYP2C9*2 and CYP2C9*3 on the pharmacokinetics of R- and S-acenocoumarol. METHODS AND RESULTS: In the first study 26 healthy volunteers with the genotype *1/*1 (n = 9), *1/*2 (n = 7), *1/*3 (n = 6), *2/*3 (n = 3), and *2/*2 (n = 1) were given 8 mg of racemic acenocoumarol as a single oral dose. Plasma R- and S-acenocoumarol concentrations were assayed at 4, 7, and 24 hours. Mean plasma S-acenocoumarol concentrations at 7 hours were higher in subjects with a variant allele; the differences were significant (P =.01) for the *1/*3 and *2/*3 genotypes. In the second study, the oral pharmacokinetics of acenocoumarol was investigated in 6 subjects (*1/*1 [n = 3] and *1/*3 [n = 3]). The mean oral clearance of S-acenocoumarol was 45% lower in the CYP2C9*1/*3 genotypes (10.9 +/- 3.0 L/h versus 19.8 +/- 3.1 L/h, P =.02). Plasma half-life was prolonged from 1.0 +/- 0.2 hours to 2.0 +/- 0.7 hours (P =.09). R-acenocoumarol pharmacokinetics did not differ between the genotypes. There was no difference in mean international normalized ratio at 24 hours, which was 1.2 in both groups. In vitro enzyme kinetics showed reduced (85%) intrinsic activity of the *3 enzyme to catalyze the hydroxylations of S-acenocoumarol. The lower activity resulted from higher Michaelis-Menten constant (2-fold) and lower maximum rate of metabolism by an enzyme-mediated reaction (by 70%). The activity of the *2 enzyme was 50% of the wild-type one. CONCLUSION: The results show S-acenocoumarol pharmacokinetics to be dependent on CYP2C9 polymorphism. In particular, the presence of the CYP2C9*3 allele impairs oral clearance of the coumarin.     

Pharmacogenetics of acenocoumarol: CYP2C9, CYP2C19, CYP1A2, CYP3A4, CYP3A5 and ABCB1 gene polymorphisms and dose requirements

BACKGROUND AND OBJECTIVE: Acenocoumarol (AC) is a coumarin derivative, vitamin K antagonist anticoagulant drug. It has a narrow therapeutic index and shows large pharmacokinetic and pharmacodynamic interindividual variability. Our objective was to investigate the association between AC dose requirements to achieve a target level of anticoagulation and genetic polymorphisms of genes possibly associated with its metabolism (CYP1A2, CYP2C9, CYP2C19, CYP3A4, CYP3A5) and transport (ABCB1). METHODS: Ninety-six Bulgarian patients treated orally with AC for at least 3 months were included. They were separated into three groups according to their AC dose requirement, i.e. low, medium and high. RESULTS AND DISCUSSION: CYP2C9*1/*3 (associated with an intermediate CYP2C9 activity), CYP2C9*2/*2, and CYP2C9*2/*3 genotypes (associated with a low CYP2C9 activity) were more prevalent in the group with low dose requirement of AC compared with the other two groups (P = 0.003). The frequency of CYP2C9*1/*1 genotype, which is associated with an extensive CYP2C9 activity, was higher in the group of patients with high dose requirements (79%), compared with the groups of the medium and low dose requirements (67% and 21% respectively). In addition, the ABCB1 2677GG/3435CC haplotype was associated with use of lower AC dose, whereas the 2677TT/3435TT and 2677GT/3435TT haplotypes were associated with use of higher AC dose (P = 0.03). The distribution of polymorphisms of other genes did not show significant differences between the three groups. CONCLUSION: In vivo, cytochromes P450 isoforms other than CYP2C9 [corrected] were not significantly associated with dose requirement of AC. In our Bulgarian patients, the presence of CYP2C9*2 or/and CYP2C9*3 alleles, as well as the ABCB1 2677GG/3435CC haplotype were associated with low dose requirement of AC.     

Effect of CYP3A5*3 genotype on the pharmacokinetics and pharmacodynamics of alprazolam in healthy subjects

OBJECTIVE: Our objective was to evaluate the effect of the CYP3A5 genotype on the pharmacokinetics and pharmacodynamics of alprazolam in healthy volunteers. METHODS: Nineteen healthy male volunteers were divided into 3 groups on the basis of the genetic polymorphism of CYP3A5. The groups comprised subjects with CYP3A5*1/*1 (n=5), CYP3A5*1/*3 (n=7), or CYP3A5*3/*3 (n=7). After a single oral 1-mg dose of alprazolam, plasma concentrations of alprazolam were measured up to 72 hours, together with assessment of psychomotor function by use of the Digit Symbol Substitution Test, according to CYP3A5 genotype. RESULTS: The area under the plasma concentration-time curve for alprazolam was significantly greater in subjects with CYP3A5*3/*3 (830.5+/-160.4 ng . h/mL [mean+/-SD]) than in those with CYP3A5*1/*1 (599.9+/-141.0 ng . h/mL) (P=.030). The oral clearance of alprazolam was also significantly different between the CYP3A5*1/*1 group (3.5+/-0.8 L/h) and CYP3A5*3/*3 group (2.5+/-0.5 L/h) (P=.036). Although a trend was noted for the area under the Digit Symbol Substitution Test score change-time curve (area under the effect curve) to be greater in subjects with CYP3A5*3/*3 (177.2+/-84.6) than in those with CYP3A5*1/*1 (107.5+/-44), the difference did not reach statistical significance (P=.148). CONCLUSIONS: The CYP3A5*3 genotype affects the disposition of alprazolam and thus influences the plasma levels of alprazolam.     

CYP2C9, but not CYP2C19, polymorphisms affect the pharmacokinetics and pharmacodynamics of glyburide in Chinese subjects

BACKGROUND: Although cytochrome P450 (CYP) 2C9 was thought to be the main pathway for glyburide (INN, glibenclamide) metabolism in vivo, studies in vitro indicated that CYP2C19 had a more dominant effect. This study investigated the relative influence of CYP2C9 and CYP2C19 genotypes on the pharmacokinetics and pharmacodynamics of glyburide in Chinese subjects. METHODS: Three groups of healthy male Chinese subjects (n=6 per group) were enrolled, as follows: group I, CYP2C9*1/*1 and CYP2C19 extensive metabolizers (EMs); group II, CYP2C9*1/*1 and CYP2C19 poor metabolizers (PMs); and group III, CYP2C9*1/*3 and CYP2C19 EMs. Subjects received single oral doses of 5 mg glyburide. Multiple blood samples were collected, and the plasma glyburide concentrations were determined by an HPLC method. The plasma glucose and insulin concentrations were also measured up to 2 hours after dosing. RESULTS: No significant differences in glyburide pharmacokinetics were observed between CYP2C19 EM and PM subjects who had the CYP2C9*1/*1 genotype (group I versus group II). Their respective values for area under the plasma concentration-time curve from time 0 to infinity (AUC0-infinity) and elimination half-life (t1/2) were 0.46+/-0.13 microg.h/mL versus 0.57+/- 0.11 microg.h/mL (P=.569) and 2.09+/-0.22 hours versus 2.24+/- 0.27 hours (P=.721). However, significant increases in AUC(0-infinity) (125% and 82%; P=.008 and .024, respectively) and t1/2 (71% and 60%; P=.003 and .007, respectively) were observed when CYP2C9*1/*3 subjects (group III) were compared with CYP2C9*1/*1 subjects in group I or II. Blood glucose reductions at 2 hours after dosing were 41.8%, 23.9%, and 27.7% in groups I, II, and III, respectively (P=.029), and hypoglycemia developed in 3 of 6 CYP2C9*1/*3 carriers and 2 of 12 CYP2C9*1/*1 carriers. CONCLUSION: CYP2C9, but not CYP2C19, polymorphism appears to exert a dominant influence on glyburide pharmacokinetics and pharmacodynamics in vivo. Further studies in diabetic patients with long-term dosing are warranted to confirm these findings.     

Contribution of age, body size, and CYP2C9 genotype to anticoagulant response to warfarin

OBJECTIVE: Our objective was to assess the contribution of CYP2C9 genotype, age, body size, and vitamin K and lipid status to warfarin dose requirements. METHODS: Patients with stable warfarin dose requirements and an international normalized ratio (INR) of the prothrombin time within the target range of 2.0 to 3.0 were recruited to the study. On arrival at the clinic in the morning, after an overnight fast, a blood sample was taken from each patient for CYP2C9 genotyping and for determination of venous INR and plasma vitamin K, R- and S-warfarin, and triglyceride concentrations. RESULTS: A total of 121 patients were recruited to the study. CYP2C9 genotyping showed that 74 patients were homozygous wild-type (*1/*1), 30 were heterozygous *1/*2, and 15 were heterozygous *1/*3 genotype. One patient was found to have the genotype *2/*3, and another was found to have the genotype *3/*3. The mean warfarin daily dose requirement in milligrams fell from 4.06 +/- 1.72 mg in homozygous wild-type patients to 3.63 +/- 1.78 mg for *1/*2-positive patients and 2.70 +/- 1.36 mg for *1/*3-positive patients. The multiple linear regression model for warfarin dose indicated significant contributions from age (r = 0.41, P <.001), genotype (r = 0.24, P <.005), and age and genotype together (r = 0.45, P <.005). Although there were significant linear correlations between warfarin dose and body surface area (r = 0.21, P =.02), body weight (r = 0.25, P =.005), and plasma vitamin K concentration (r = 0.18, P <.05), none of these variables made a significant contribution to the regression model for warfarin dose. CYP2C9 genotype had a significant effect on S-warfarin clearance (r = 0.34, P <.0001) but none on R-warfarin clearance. CONCLUSION: This study showed that age and CYP2C9 polymorphism affect warfarin dose requirements in patients receiving long-term therapy and having stable control of anticoagulation. It is anticipated that using dosing regimens modified to take into account the contribution of age and CYP2C9 genotype has the potential to improve the safety of warfarin therapy.     

Effect of the CYP3A5 genotype on the pharmacokinetics of intravenous midazolam during inhibited and induced metabolic states

OBJECTIVE: Our objective was to investigate the effect of the CYP3A5 genotype on the systemic clearance of midazolam in constitutive, inhibited, and induced metabolic conditions. METHODS: Nineteen healthy volunteers were grouped with regard to the CYP3A5*3 allele, into homozygous wild-type (CYP3A5*1/*1, n = 6), heterozygous (CYP3A5*1/*3, n = 6), and homozygous variant-type (CYP3A5*3/*3, n = 7) subject groups. The pharmacokinetic profile of intravenous midazolam was characterized before and after itraconazole administration (200 mg once daily for 4 days) and also after rifampin (INN, rifampicin) pretreatment (600 mg once daily for 10 days), with a washout period of 2 weeks in between. RESULTS: The pharmacokinetic profiles of midazolam and of its hydroxy metabolites did not show differences between the genotype groups under basal and induced metabolic conditions. However, during the inhibited metabolic state, the CYP3A5*3/*3 group showed a greater decrease in systemic clearance than was seen in the CYP3A5*1/*1 group (8.5 +/- 3.8 L. h(-1). 70 kg(-1) versus 13.5 +/- 2.7 L. h(-1). 70 kg(-1), P =.027). The 1'-hydroxymidazolam-to-midazolam area under the plasma concentration-time curve ratio was also significantly lower in the CYP3A5*3/*3 group (0.58 +/- 0.35 versus 1.09 +/- 0.37 for the homozygous wild-type group, P =.026). CONCLUSIONS: The CYP3A5 genotype did not affect the pharmacokinetics of intravenous midazolam in the basal or induced states. However, during cytochrome P450 (CYP) 3A inhibition by itraconazole, individuals carrying the CYP3A5*1 allele were found to be less susceptible to changes in systemic clearance and showed higher 1'-hydroxymidazolam-to-midazolam area under the plasma concentration-time curve ratios, probably resulting from the relatively CYP3A4-specific inhibition caused by itraconazole.     

Genetic polymorphism of cytochrome P450 1A1 (Cyp1A1) and glutathione transferases (M1, T1 and P1) among Africans.

The co-ordinate expression and regulation of the drug metabolising enzymes, cytochrome P4501A1 (CYPlAl) and glutathione transferases (GSTM1, GSTT1 and GSTP1), and their metabolic balance in the cells of target organs may determine whether exposure to carcinogens results in cancer. Besides showing variability in activity due to induction and inhibition, these enzymes also exhibit genetic polymorphism that alter enzyme levels and activity. We determined frequencies of common allelic variants of CYP1A1 and glutathione (M1, T1 and P1) among Tanzanians, South African Venda and Zimbabweans using PCR/restriction fragment length polymorphism techniques. The CYP1A1 Val462 mutant variant was found at a frequency of 1.3% among 114 subjects. The GSTM1*0 genotype was found at a frequency of 29% and 33% among Tanzanian psychiatric patients and healthy volunteers, respectively. Similarly, the GSTT1*0 polymorphism was present with a frequency of 25% in both the psychiatric patients and healthy controls. The frequency of GSTP1 Val105 variant was 16%, 12% and 21% among Tanzanians, South African Venda and Zimbabweans, respectively. We conclude here that CYP1A1 Val462 polymorphism is very rare among Africans. This is the first report of the GSTP1 Val105 variant frequency in African populations. We show here that there are no differences in frequencies of the variant alleles for CYP1A1, GSTM1, GSTT1 and GSTP1 in the three African populations.     

ABCB1 and cytochrome P450 genotypes and phenotypes: influence on methadone plasma levels and response to treatment

BACKGROUND AND OBJECTIVE: The in vivo implication of various cytochrome P450 (CYP) isoforms and of P-glycoprotein on methadone kinetics is unclear. We aimed to thoroughly examine the genetic factors influencing methadone kinetics and response to treatment. METHODS: Genotyping for CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, ABCB1, and UGT2B7 polymorphisms was performed in 245 patients undergoing methadone maintenance treatment. To assess CYP3A activity, the patients were phenotyped with midazolam. RESULTS: The patients with lower CYP3A activity presented higher steady-state trough (R,S)-methadone plasma levels (4.3, 3.0, and 2.3 ng/mL x mg for low, medium, and high activity, respectively; P = .0002). As previously reported, CYP2B6*6/*6 carriers had significantly higher trough (S)-methadone plasma levels (P = .0001) and a trend toward higher (R)-methadone plasma levels (P = .07). CYP2D6 ultrarapid metabolizers presented lower trough (R,S)-methadone plasma levels compared with the extensive or intermediate metabolizers (2.4 and 3.3 ng/mL x mg, respectively; P = .04), whereas CYP2D6 poor metabolizer status showed no influence. ABCB1 3435TT carriers presented lower trough (R,S)-methadone plasma levels (2.7 and 3.4 ng/mL . mg for 3435TT and 3435CC carriers, respectively; P = .01). The CYP1A2, CYP2C9, CYP2C19, CYP3A5, and UGT2B7 genotypes did not influence methadone plasma levels. Only CYP2B6 displayed a stereoselectivity in its activity. CONCLUSION: In vivo, CYP3A4 and CYP2B6 are the major CYP isoforms involved in methadone metabolism, with CYP2D6 contributing to a minor extent. ABCB1 genetic polymorphisms also contribute slightly to the interindividual variability of methadone kinetics. The genetic polymorphisms of these 4 proteins had no influence on the response to treatment and only a small influence on the dose requirement of methadone.     

Effects of cytochrome P450 2C9 polymorphisms on phenprocoumon anticoagulation status

OBJECTIVE: Our objective was to assess whether there is an association between the presence of allelic variants of the gene for cytochrome P450 (CYP) 2C9 and anticoagulation problems during the initial phase of phenprocoumon treatment. METHODS: A prospective follow-up study was performed at 2 anticoagulation clinics in The Netherlands. Included subjects started phenprocoumon during the study period, had their first check of the international normalized ratio (INR) on the third or fourth day of therapy, and had an indication for the low therapeutic range (INR, 2.0-3.5). CYP2C9 genotypes ( CYP2C9*1 , CYP2C9*2 , and CYP2C9*3 ) were assessed, and data on indication, INR checks, comedication, and comorbidity were collected. RESULTS: After genotyping, 284 subjects were available for analysis. Of these, 186 (65.5%) were homozygous carriers of the CYP2C9 wild-type allele ( CYP2C9*1/*1 ), 61 (21.5%) were carriers of the CYP2C9*2 allele, and 37 (13.0%) were carriers of the CYP2C9*3 allele. Compared with homozygous CYP2C9*1/*1 subjects, carriers of CYP2C9*2 or *3 had an increased risk of severe overanticoagulation (INR >6.0). The hazard ratio for CYP2C9*2 versus CYP2C9*1/*1 was 3.09 (95% confidence interval [CI], 1.56 to 6.13; P=.001), and the hazard ratio for CYP2C9*3 versus CYP2C9*1/*1 was 2.40 (95% CI, 1.03 to 5.57; P=.042). Carriers of CYP2C9*2 also had a lower chance to achieve stability in the follow-up period. The hazard ratio for CYP2C9*2 versus CYP2C9*1/*1 was 0.61 (95% CI, 0.43 to 0.85; P=.003). Carriers of the CYP2C9*2 or *3 allele needed a significantly lower phenprocoumon dosage compared with homozygous CYP2C9*1/*1 subjects. CONCLUSION: The presence of at least 1 CYP2C9*2 or *3 allele in phenprocoumon users is associated with an increased risk of severe overanticoagulation. Similar to warfarin and acenocoumarol, phenprocoumon had a lower dosage requirement in carriers of CYP2C9*2 or *3 compared with that in CYP2C9 wild-type subjects.     

A variant 2677A allele of the MDR1 gene affects fexofenadine disposition

BACKGROUND AND OBJECTIVES: There have been considerable disagreements regarding the influence of MDR1 (ABCB1) polymorphisms on the disposition of P-glycoprotein (P-gp) substrates. We speculated that the unknown function of the A allele of exon 21 G2677T/A (Ala893Ser/Thr) provides one of the reasons for the contradictory results. This study was performed to clarify the effects of major MDR1 gene polymorphisms, including a variant A allele in exon 21, on fexofenadine pharmacokinetics. METHODS: We investigated the occurrence of 3 high-frequency single-nucleotide polymorphisms (SNPs) in exons 12 (C1236T), 21 (G2677T/A), and 26 (C3435T) of the MDR1 gene in 232 healthy Koreans, using a polymerase chain reaction-restriction fragment length polymorphism method, and performed haplotype analysis on these 3 SNPs. A single oral dose of 180 mg fexofenadine hydrochloride was administered to 33 healthy Korean male volunteers, who were divided into 6 groups based on the MDR1 genotype for the G2677T/A polymorphism in exon 21 and the C3435T polymorphism in exon 26. RESULTS: A strong linkage disequilibrium was observed among the 3 SNPs. The frequencies of the 4 major haplotypes, 1236C-2677A-3435C, C-G-C, T-G-C, and T-T-T, were 16.4%, 18.6%, 21.6%, and 32.2%, respectively. Fexofenadine disposition varied considerably among the groups. In the 2677AA/3435CC genotype group (n=3), the values of area under the concentration-time curve from time 0 to 24 hours [AUC(0-24)] were significantly lower (P=.014) than those of the other 5 genotype groups (GG/CC, GT/CT, TT/TT, GA/CC, and TA/CT). As compared with the 2677GG/3435CC subjects, the AUC(0-24) values were 17% lower in the 2677AA/3435CC subjects and 47% higher in the 2677TT/3435TT subjects (GG/CC versus AA/CC versus TT/TT, 4017 +/- 1137 ng . h/mL versus 3315 +/- 958 ng . h/mL versus 5934 +/- 2,064 ng . h/mL; P=.018). By stratification for genotypes at position 3435, homozygous 3435TT subjects were found to have significantly higher AUC(0-24) (P=.024) and maximum plasma concentration (P=.040) values than CC subjects [AUC(0-24), 5934 +/- 2064 ng . h/mL versus 3998 +/- 1241 ng . h/mL; maximum plasma concentration, 958 +/- 408 ng/mL versus 673 +/- 242 ng/mL]. CONCLUSIONS: The plasma concentrations of fexofenadine after a single oral administration were lower in 2677AA/3435CC subjects than in subjects with the other 5 genotype combinations of the SNPs of G2677T/A and C3435T. These findings confirm the importance of analyzing MDR1 haplotypes and provide a plausible explanation for the conflicting results regarding the effect of MDR1 polymorphisms on the disposition of P-gp substrates.     

CYP2C9 polymorphisms and the interindividual variability in pharmacokinetics and pharmacodynamics of the loop diuretic drug torsemide

INTRODUCTION: According to in vitro data, torsemide (INN, torasemide) is a substrate of the genetically polymorphic enzyme cytochrome P450 (CYP) 2C9, but the impact of CYP2C9 polymorphisms on torsemide pharmacokinetics and pharmacodynamics has not been studied in humans. METHODS: A total of 36 healthy volunteers (12, 9, 1, 9, 3, and 2 carriers of CYP2C9 genotypes *1/*1 , *1/*2 , *2/*2 , *1/*3 , *2/*3 , and *3/*3 , respectively) received a single oral dose of 10 mg torsemide for pharmacokinetic and pharmacodynamic analysis. The effects of the CYP2C9 polymorphism on torsemide-induced urine volume and urinary elimination of sodium, potassium, chloride, and uric acid were measured during a salt-restricted diet. RESULTS: Median torsemide total oral clearance values were 3.4, 2.2, and 1.2 L/h in carriers of the CYP2C9 genotypes *1/*1 , *1/*3 , and *3/*3 , respectively, but there was no significant difference related to CYP2C9*2 . Values for metabolite formation clearance via metabolites M1 and M5 were 1.4, 1.7, 1.4, 1.0, 0.77, and 0.18 L/h in carriers of genotypes *1/*1 , *1/*2 , *2/*2 , *1/*3 , *2/*3 , and *3/*3 , respectively (P < .001). From 0 to 8 hours after torsemide administration, Na + , K + , and Cl - elimination was higher in carriers of CYP2C9*3 alleles than in carriers of the homozygous wild-type genotype, and 24-hour uric acid elimination values in urine were 451, 350, and 249 mg in carriers of 0, 1, and 2 CYP2C9*3 alleles, respectively (P = .003). CONCLUSION: Torsemide pharmacokinetics differed significantly between subgroups with different CYP2C9 genotypes, and diuretic effects were slightly more exaggerated in carriers of CYP2C9*3 alleles. To answer the question of whether these findings have clinical implications, further studies in patients undergoing long-term torsemide treatment are required.     

武汉地区冠心病患者氯吡格雷药物代谢相关基因CYP2C19的多态性分布分析

目的 探讨武汉地区冠心病介入患者氯吡格雷代谢相关基因CYP2C19多态性的分布。方法 选取2014年1月～12月武汉大学人民医院心内科进行介入治疗(PCI)的316例冠心病患者作为研究对象。通过基因芯片法检测氯吡格雷代谢相关的CYP2C19*1,*2,*3基因,并将患者按CYP2C19基因型别分为不同代谢类型:强代谢型(*1/*1),中间代谢型(*1/*2,*1/*3),弱代谢型(*2/*2,*3/*3,*2/*3)。结果 根据CYP2C19基因多态性位点功能代谢分型,携带CYP2C19*1的强代谢型(*1/*1)占43.4%,携带CYP2C19*2或*3的中间代谢型(*1/*2和*1/*3)及弱代谢型(*2/*2,*2/*3和*3/*3)分别占42.4%,14.2%。不同性别在CYP2C19基因分型上差异无统计学意义。结论 武汉地区冠心病介入患者中分布有较多的CYP2C19氯吡格雷代谢功能缺失基因。     

Personalized Tacrolimus Doses Determined by CYP3A5 Genotype for Induction and Maintenance Phases of Kidney Transplantation

Background

Cytochrome P450 (CYP) 3A4 and 3A5 are major isoforms involved in the metabolism of tacrolimus, with the CYP3A5 gene being more polymorphic. It is hypothesized that individual variation in the metabolism of tacrolimus drug may result from genetic polymorphism of CYP3A5. It has been reported that the clearance of tacrolimus in patients with the CYP3A5*1 allele was ~2.5-fold greater than that in those with the CYP3A5*3/*3 genotype. Recent data have also shown that polymorphism in exon 26 (C3435T) of the multidrug resistance gene (MDR1) was correlated with the expression level and function of P-glycoprotein in the lower duodenum, making the relationship between polymorphism of MDR1 and the effective dose of tacrolimus a source of controversy.

Objectives

This study investigated the influence of genetic polymorphisms of CYP3A5 and MDR1 on the dose requirements for the induction and maintenance phases of tacrolimus therapy in kidney transplant recipients.

Methods

Sixty-eight kidney transplant recipients were enrolled, and their clinical and laboratory data were retrospectively reviewed after 6 months of tacrolimus administration. Genotypes of CYP3A5*1 and CYP3A5*3 and exon 26 of MDR1 (C3435T) were determined by the single-nucleotide polymorphism genotyping method.

Results

The frequencies of CYP3A5*3/*3, CYP3A5*1/*3, and CYP3A5*1/*1 were 44.1%, 35.3%, and 20.6%, respectively. The mean dose of tacrolimus required for the induction phase was significantly greater in the CYP3A5*1/*1 group (0.142 [0.050] mg/kg/d) than that required in the CYP3A5*1/*3 group (0.097 [0.040] mg/kg/d; P = 0.072) and in the CYP3A5*3/*3 group (0.077 [0.020] mg/kg/d; P = 0.005). The maintenance dose of tacrolimus required in the CYP3A5*1/*1 group (0.12 [0.03] mg/kg/d) was 1.3-fold higher than that in the CYP3A5*1/*3 group (0.09 [0.03] mg/kg/d; P = 0.018) and 2.4-fold higher than in the CYP3A5*3/*3 group (0.05 [0.02] mg/kg/d; P < 0.0001). No statistically significant relationship was observed between the doses of tacrolimus required for the induction and maintenance phases and MDR1 polymorphism.

Conclusion

Determination of the CYP3A5 genotype would be helpful in the design of adequate immunosuppressive treatment and in lowering toxicity by predicting the doses of tacrolimus required for the induction and maintenance phases in individual kidney transplant recipients.     

Effects of organic anion transporting polypeptide 1B1 haplotype on pharmacokinetics of pravastatin, valsartan, and temocapril

OBJECTIVE: Recent reports have shown that genetic polymorphisms in organic anion transporting polypeptide (OATP) 1B1 have an effect on the pharmacokinetics of drugs. However, the impact of OATP1B1*1b alleles, the frequency of which is high in all ethnicities, on the pharmacokinetics of substrate drugs is not known after complete separation of subjects with OATP1B1*1a and *1b. Furthermore, the correlation between the clearances of OATP1B1 substrate drugs in individuals has not been characterized. We investigated the effect of genetic polymorphism of OATP1B1, particularly the *1b allele, on the pharmacokinetics of 3 anionic drugs, pravastatin, valsartan, and temocapril, in Japanese subjects. METHODS: Twenty-three healthy Japanese volunteers were enrolled in a 3-period crossover study. In each period, after a single oral administration of pravastatin, valsartan, or temocapril, plasma and urine were collected for up to 24 hours. RESULTS: The area under the plasma concentration-time curve (AUC) of pravastatin in *1b/*1b carriers (47.4 +/- 19.9 ng.h/mL) was 65% of that in *1a/*1a carriers (73.2 +/- 23.5 ng.h/mL) (P = .049). Carriers of *1b/*15 (38.2 +/- 15.9 ng.h/mL) exhibited a 45% lower AUC than *1a/*15 carriers (69.2 +/- 23.4 ng.h/mL) (P = .024). In the case of valsartan we observed a similar trend as with pravastatin, although the difference was not statistically significant (9.01 +/- 3.33 microg.h/mL for *1b/*1b carriers versus 12.3 +/- 4.6 microg.h/mL for *1a/*1a carriers [P = .171] and 6.31 +/- 3.64 microg.h/mL for *1b/*15 carriers versus 9.40 +/- 4.34 microg.h/mL for *1a/*15 carriers [P = .213]). The AUC of temocapril also showed a similar trend (12.4 +/- 4.1 ng.h/mL for *1b/*1b carriers versus 18.5 +/- 7.7 ng.h/mL for *1a/*1a carriers [P = .061] and 16.4 +/- 5.0 ng.h/mL for *1b/*15 carriers versus 19.0 +/- 4.1 ng.h/mL for *1a/*15 carriers [P = .425]), whereas that of temocaprilat (active form of temocapril) was not significantly affected by the haplotype of OATP1B1. Interestingly, the AUC of valsartan and temocapril in each subject was significantly correlated with that of pravastatin (R = 0.630 and 0.602, P < .01). The renal clearance remained unchanged for each haplotype for all drugs. CONCLUSION: The major clearance mechanism of pravastatin, valsartan, and temocapril appears to be similar, and OATP1B1*1b is one of the determinant factors governing the interindividual variability in the pharmacokinetics of pravastatin and, possibly, valsartan and temocapril.     

CYP2C8 *3 and *4 define CYP2C8 phenotype: An approach with the substrate cinitapride

Cinitapride is a gastrointestinal prokinetic drug, prescribed for the treatment of functional dyspepsia, and as an adjuvant therapy for gastroesophageal reflux disease. In this study, we aimed to explore the impact of relevant variants in CYP3A4 and CYP2C8 and other pharmacogenes, along with demographic characteristics, on cinitapride pharmacokinetics and safety; and to evaluate the impact of CYP2C8 alleles on the enzyme''s function. Twenty‐five healthy volunteers participating in a bioequivalence clinical trial consented to participate in the study. Participants were genotyped for 56 variants in 19 genes, including cytochrome P450 (CYP) enzymes (e.g., CYP2C8 or CYP3A4) or transporters (e.g., SLC or ABC), among others. CYP2C8*3 carriers showed a reduction in AUC of 42% and C_max of 35% compared to *1/*1 subjects (p = 0.003 and p = 0.011, respectively). *4 allele carriers showed a 45% increase in AUC and 63% in C_max compared to *1/*1 subjects, although these differences did not reach statistical significance. CYP2C8*3 and *4 alleles may be used to infer the following pharmacogenetic phenotypes: ultrarapid (UM) (*3/*3), rapid (RM) (*1/*3), normal (NM) (*1/*1), intermediate (IM) (*1/*4), and poor (PM) metabolizers (*4/*4). In this study, we properly characterized RMs, NMs, and IMs; however, additional studies are required to properly characterize UMs and PMs. These findings should be relevant with respect to cinitapride, but also to numerous CYP2C8 substrates such as imatinib, loperamide, montelukast, ibuprofen, paclitaxel, pioglitazone, repaglinide, or rosiglitazone.