Enantiospecific effects of cytochrome P450 2C9 amino acid variants on ibuprofen pharmacokinetics and on the inhibition of cyclooxygenases 1 and 2

OBJECTIVE: According to in vitro data, the polymorphic cytochrome P450 enzyme 2C9 (CYP2C9) may be the major S-ibuprofen hydroxylase. In humans, there are 2 variants of CYP2C9 with a high population frequency. We studied their impact on ibuprofen pharmacokinetics and on the inhibition of cyclooxygenases 1 and 2. METHODS: Kinetics of an oral dose of 600 mg racemic ibuprofen were studied in 21 healthy volunteers with all combinations of the CYP2C9 variants *2 (arginine144cysteine) and *3 (isoleucine359leucine). Blood concentrations of racemic ibuprofen and of S-(+)-ibuprofen and R-(-)-ibuprofen were measured by HPLC, and thromboxane B(2) and prostaglandin E(2) were measured with use of an enzyme immunoassay. Data were evaluated with a population pharmacokinetic model that integrated pharmacogenetic information. RESULTS: The pharmacokinetics of racemic and of S-ibuprofen depended on the CYP2C9 isoleucine359leucine amino acid polymorphism: population mean S-ibuprofen clearances were 3.25 L/h (95% confidence interval [CI], 2.84 to 3.73), 2.38 L/h (95% CI, 2.09 to 2.73), and 1.52 L/h (95% CI, 1.33 to 1.74) in carriers of the CYP2C9 genotypes *1/*1, *1/*3, and *3/*3, respectively. The CYP2C9 variant *2 exhibited no significant effect. Ex vivo formation of thromboxane B(2), reflecting cyclooxygenase type 1 inhibition, depended significantly on the CYP2C9 polymorphism. The maximal inhibition of thromboxane B(2) formation and the area under the effect-time curve were larger in carriers of the slow CYP2C9 genotypes *1/*3, *2/*3, and *3/*3 than in *1/*1 carriers; the same trend was observed for prostaglandin E(2), reflecting cyclooxygenase type 2 inhibition. CONCLUSIONS: The reduced S-ibuprofen total clearance accompanied by increased pharmacodynamic activity may have medical impact in patients receiving ibuprofen.     

Pharmacokinetics and pharmacodynamics of rosiglitazone in relation to CYP2C8 genotype

OBJECTIVES: Rosiglitazone is metabolically inactivated predominantly via the cytochrome P450 (CYP) enzyme CYP2C8. The functional impact of the CYP2C8*3 allele coding for the Arg139Lys and Lys399Arg amino acid substitutions is controversial. The purpose of this was to clarify the role of this polymorphism with regard to the pharmacokinetics and clinical effects of rosiglitazone. METHODS: From a large sample of healthy volunteers, 14 carriers of the CYP2C8*1/*1 allele, 13 carriers of the *1/*3 allele, and 4 carriers the *3/*3 allele were selected for a clinical study. Rosiglitazone (8 mg) single-dose and multiple-dose pharmacokinetics and its effects on glucose level and body weight were monitored. Plasma and urine concentrations of rosiglitazone and desmethylrosiglitazone were measured, and kinetics was analyzed by noncompartmental and population-kinetic compartmental methods. RESULTS: Mean total clearance values were 0.033 L x h(-1) x kg(-1) (95% confidence interval [CI], 0.030-0.037 L x h(-1) x kg(-1)), 0.038 L x h(-1) x kg(-1) (95% CI, 0.033-0.044 L x h(-1) x kg(-1)), and 0.046 L x h(-1) x kg(-1) (95% CI, 0.033-0.058 L x h(-1) x kg(-1)) in carriers of CYP2C8 genotypes *1/*1, *1/*3, and *3/*3, respectively, on day 1 (P = .02, ANOVA [F test]). Rosiglitazone kinetics could be adequately described by a 1-compartmental model with first-order absorption. Besides CYP2C8 genotype, body weight was a significant covariate (P < .001, log-likelihood ratio test). Elimination half-lives were 4.3, 3.5, and 2.9 hours in CYP2C8*1/*1, *1/*3, and *3/*3 carriers, respectively. Clearance of desmethylrosiglitazone was also higher in CYP2C8*3 allele carriers, with mean values of 1.96 L/h (95% CI, 1.42-2.69 L/h), 2.22 L/h (95% CI, 1.61-3.04 L/h), and 2.47 L/h (95% CI, 1.80-3.39 L/h), respectively (P = .03). The plasma glucose area under the concentration curve was significantly lower after 14 days of taking rosiglitazone compared with day 1 (P = .01, paired t test), but no relationship of the glucose-lowering effect of rosiglitazone with CYP2C8 genotype was observed. CONCLUSIONS: This study showed that the CYP2C8*3 allele confers higher in vivo metabolic capacity than the wild-type CYP2C8*1 allele but the pharmacokinetic differences resulting from CYP2C8*3 were quantitatively moderate.     

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.     

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.     

CYP2C9 and CYP2C19 genetic polymorphisms: frequencies in the south Indian population

The aim of the study was to establish the frequencies of CYP2C9*1, *2, *3 and CYP2C19*1, *2 and *3 in the south Indian population and to compare them with the inter-racial distribution of the CYP2C9 and CYP2C19 genetic polymorphisms. Genotyping analyses of CYP2C9 and CYP2C19 were conducted in unrelated, healthy volunteers from the three south Indian states of Andhra Pradesh, Karnataka and Kerala, by the polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP). The allele frequencies of the populations of these three states were then pooled with our previous genotyping data of Tamilians (also in south India), to arrive at the distribution of CYP2C9 and CYP2C19 alleles in the south Indian population. Frequencies of CYP2C9 and CYP2C19 alleles and genotypes among various populations were compared using the two-tailed Fisher's exact test. The frequencies of CYP2C9*1, *2 and *3 in the south Indian population were 0.88 (95% CI 0.85-0.91), 0.04 (95% CI 0.02-0.06) and 0.08 (95% CI 0.06-0.11), respectively. The frequencies of CYP2C9 genotypes *1/*1, *1/*2, *1/*3, *2/*2, *2/*3 and *3/*3 were 0.78 (95% CI 0.74-0.82), 0.05 (95% CI 0.03-0.07), 0.15 (95% CI 0.12-0.18), 0.01 (95% CI 0.0-0.02), 0.01 (95% CI 0.0-0.02) and 0.0, respectively. CYP2C19*1, *2 and *3 frequencies were 0.64 (95% CI 0.60-0.68), 0.35 (95% CI 0.31-0.39) and 0.01 (95% CI 0.0-0.03), respectively. As a result of a significant heterogeneity, the data on CYP2C19 genotype frequencies were not pooled. The frequency of CYP2C9*2 mutant alleles in south Indians was higher than in Chinese and Caucasians, while CYP2C9*3 was similar to Caucasians. CYP2C19*2 was higher than in other major populations reported so far. The relatively high CYP2C19 poor-metabolizer genotype frequency of 12.6% indicates that over 28 million south Indians are poor metabolizers of CYP2C19 substrates.     

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.     

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.     

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.     

CYP2C19 genotype affects diazepam pharmacokinetics and emergence from general anesthesia

OBJECTIVES: Diazepam is widely used to relieve preoperative anxiety in patients. The objective of this study was to investigate the effects of polymorphism in CYP2C19 and the effects of CYP3A4 messenger ribonucleic acid (mRNA) content in blood on recovery from general anesthesia and on diazepam pharmacokinetics. METHODS: Sixty-three Japanese patients were classified into the following 3 genotype (phenotype) groups on the basis of polymerase chain reaction-restriction fragment length polymorphism analysis of CYP2C19 polymorphism: no variants, *1/*1 (extensive metabolizer [EM]); 1 variant, *1/*2 or *1/*3 (intermediate metabolizer [IM]); and 2 variants, *2/*2, *2/*3, or *3/*3 (poor metabolizer [PM]). We assessed the effects of these polymorphisms and of CYP3A4 mRNA content in the lymphocytes on the patients' recovery from general anesthesia. RESULTS: CYP2C19 genotyping analysis in the 63 subjects showed that 32%, 46%, and 22% of subjects were classified into the EM, IM, and PM groups, respectively. The PM subjects showed a larger area under the curve representing the concentration of diazepam over a 24-hour period (AUC(0-24)) (2088 +/- 378 ng/mL.h(-1), P = .0259), lower clearance of diazepam (0.049 +/- 0.009 L.h(-1).kg(-1), P = .0287), and longer emergence time (median, 18 minutes; 25th-75th percentile range, 13-21 minutes; P < .001) in comparison with subjects in the EM group (AUC(0-24), 1412 +/- 312 ng/mL; clearance, 0.074 +/- 0.018 L.h(-1).kg(-1); and emergence time, 10 minutes, 8-12 minutes [median and 25th-75th percentile range]). The IM group also showed a longer emergence time (median, 13 minutes; 25th-75th percentile range, 9-20 minutes; P < .001) and a larger variation in this parameter in comparison with the EM group. The distributions of the CYP2C19 genotype were significantly different between the 2 groups (rapid emergence <20 minutes, slow emergence >20 minutes) (P = .0148). The mean value of the CYP3A4 mRNA level in the slow-emergence group (mean +/- SD, 4.80 +/- 3.99 x10(-10)) was significantly lower than that of the rapid-emergence group (mean +/- SD, 12.50 +/- 11.90 x10(-10)) (P = .0315). However, there was no significant correlation between emergence time and CYP3A4 mRNA levels (r = 0.239, P = .0601). CONCLUSION: We found that the CYP2C19 genotype affects diazepam pharmacokinetics and emergence from general anesthesia and that the slow-emergence group possesses lower levels of CYP3A4 mRNA than are found in the rapid-emergence group.     

Influence of CYP2C9 polymorphisms on the pharmacokinetics and cholesterol-lowering activity of (-)-3S,5R-fluvastatin and (+)-3R,5S-fluvastatin in healthy volunteers

INTRODUCTION: In vitro data indicate that biotransformation of the synthetic 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor fluvastatin is catalyzed by the cytochrome P450 (CYP) enzyme 2C9. The consequences of CYP2C9 genetic polymorphisms on fluvastatin pharmacokinetics and on its efficacy have not been investigated in humans thus far. METHODS: Twenty-four healthy heterozygous or homozygous carriers of the CYP2C9 variants Arg144Cys (*2) and Ile359Leu (*3) and 2 individuals with the deficient CYP2D6 genotype *4/*4 took 40 mg racemic fluvastatin daily for 14 days. All subjects had also been genotyped for CYP2C8, CYP2C19, and CYP2D6 polymorphisms. Pharmacokinetics was analyzed after the first fluvastatin administration. Serum lipid concentrations were measured before fluvastatin intake and on day 15. Plasma concentrations of (+)-3R,5S-fluvastatin and of (-)-3S,5R-fluvastatin were quantified by enantiospecific HPLC. RESULTS: Pharmacokinetics of both enantiomers showed statistically significant differences according to the number of CYP2C9*3 alleles (P <.0001, F test). Mean (and SD) values for area under the curve of the active (+)-3R,5S-fluvastatin in carriers of the genotype CYP2C9*1/*1, *1/*3, and *3/*3 were 173 (85) micro g. L(-1). h, 231 (85) micro g. L(-1). h, and 533 (120) micro g. L(-1). h, respectively. The corresponding values for area under the curve of (-)-3S,5R-fluvastatin were 227 (133) micro g. L(-1). h, 360 (103) micro g. L(-1). h, and 1126 (311) micro g. L(-1). h for CYP2C9*1/*1, *1/*3, and *3/*3, respectively. The CYP2C9*2 variant did not have any significant influence on fluvastatin kinetics, nor did the CYP2C8*3 allele, which was tightly linked with CYP2C9*2. Total serum cholesterol and low-density lipoprotein cholesterol concentrations decreased significantly during the 14-day treatment period (P <.001), but no correlation with the CYP2C9 genotype was found. CONCLUSIONS: The pharmacokinetics of both enantiomers of fluvastatin depended on the CYP2C9 genotype, with a 3-fold group mean difference in the active enantiomer and even greater differences in the inactive enantiomer, but differences in plasma concentrations were not reflected in cholesterol lowering after 14 days of fluvastatin intake in healthy volunteers.     

Polymorphism in CYP2C8 is associated with reduced plasma concentrations of repaglinide

OBJECTIVE: Our objective was to investigate the effects of genetic polymorphisms of cytochrome P450 (CYP) 2C8 on the pharmacokinetics and pharmacodynamics of the meglitinide analog antidiabetic drug repaglinide. METHODS: We genotyped 28 healthy volunteers who had participated in our pharmacokinetic studies on repaglinide for variant alleles of the CYP2C8 gene. Each subject ingested a 0.25-mg dose of repaglinide, and plasma drug and blood glucose concentrations were monitored for 7 hours after dosing. RESULTS: There were 19 subjects (68%) with the CYP2C8*1/*1 genotype (wild type), 6 subjects (21%) with the CYP2C8*1/*3 genotype, and 3 subjects (11%) with the CYP2C8*1/*4 genotype. In the 3 genotypic groups, the mean +/- SD area under the plasma repaglinide concentration-time curve from time 0 to infinity [AUC(0- infinity )] was 5.8 +/- 2.5 ng. h/mL for CYP2C8*1/*1, 3.6 +/- 0.9 ng. h/mL for CYP2C8*1/*3, and 5.1 +/- 3.6 ng. h/mL for CYP2C8*1/*4. The mean AUC(0- infinity ) of repaglinide was 45% (P <.005) lower and the peak concentration in plasma was 39% lower (P <.05) in subjects with the CYP2C8*1/*3 genotype compared with those with the CYP2C8*1/*1 genotype. No statistically significant differences were found in the blood glucose response to repaglinide between the genotypes. CONCLUSIONS: Unexpectedly, the CYP2C8*3 variant allele was associated with reduced plasma concentrations of repaglinide. The effects of CYP2C8 polymorphisms on the pharmacokinetics of CYP2C8 substrates warrant further study.     

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.     

Warfarin metabolism and anticoagulant effect: a prospective, observational study of the impact of CYP2C9 genetic polymorphism in the presence of drug-disease and drug-drug interactions

BACKGROUND: Cytocbrome P450 (CYP) 2C9 polymorphism affects the warfarin dosage requirement in stable outpatients. However, it is not known whether the CYP2C9 genotype contributes to the variability in warfarin dosage in the presence of drug-disease and drug-drug interactions. OBJECTIVE: The aim of this study was to examine the effects of CYP2C9 genetic polymorphism on warfarin dosage requirements in patients with severe comorbid conditions and those treated with medications that potentially interact with warfarin. METHODS: This prospective, observational study was conducted at Hadassah University Hospital, Jerusalem, Israel. Data from consecutive patients treated with warfarin for at least 3 months and admitted to the internal medicine ward were eligible for inclusion. Clinical data, international normalized ratio (INR), and warfarin dosage were recorded from medical records. The CYP2C9 genotype was determined using polymerase chain reaction restriction fragment length polymorphism, and plasma concentrations of (S)- and (R)-warfarin were determined by high-performance liquid chromatography using chiral methods. RESULTS: One hundred nineteen subjects (52% women) were studied. Mean age was 65.8 years (95% CI, 63.1-68.4), and weight was 74.9 kg (95% CI, 72.1-77.7). The mean warfarin dosage was 33% lower in patients with the CYP2C9-*1/*3 genotype (mean [SEM], 0.045 [0.006] mg/kg x d(-1)) compared with the CYP2C9-*1/*1 genotype (0.067 [0.004] mg/kg x d(-1)) (P=0.008); an intermediate value was found for the CYP2C9-*1/*2 genotype (0.062 [0.008] mg/kg x d(-1)). However, despite the lower dosage, INR was significantly higher in patients with the *1/*3 genotype (mean [95% CI], 3.29 [2.44-4.14]) (n=18) compared with the *1/*1 genotype (2.52 [2.34-2.71]) (n=64) (P=0.029). In addition to genotype, older age, congestive heart failure (CHF), and treatment with antibiotics were associated with lower warfarin dosages, whereas treatment with drug-metabolism inducers was associated with higher warfarin dosages. In addition, the ratios of (S)- to (R)-warfarin concentrations were significantly higher in patients with *1/*3 compared with those in patients with the *1/*1 genotype. CONCLUSIONS: In this study population of patients with severe comorbid conditions and those treated with medications that potentially interact with warfarin, CYP2C9 *1/*3 genotype, older age, CHF, and the use of antibiotics were associated with lower warfarin dosage requirements. The CYP2C9*1/*3 genotype, compared with CYP2C9 *1/*1, was associated with 33% lower mean warfarin dosage requirements and higher INR values, which were higher than the upper therapeutic range of INR (ie, 3). Genetic CYP2C9 polymorphism contributed to the variability in warfarin dosage requirements in the presence of drug-disease and drug-drug interactions.     

Impact of CYP2C9 amino acid polymorphisms on glyburide kinetics and on the insulin and glucose response in healthy volunteers

BACKGROUND: Glyburide (INN, glibenclamide) is a second-generation sulfonylurea antidiabetic agent with high potency. We hypothesized that glyburide may be a substrate of cytochrome P450 2C9 (CYP2C9), an enzyme that has two low-activity amino acid variants-Arg144Cys (CYP2C9*2) and Ile359Leu (CYP2C9*3). We explored the impact of these polymorphisms on glyburide pharmacokinetics and the effects on insulin and glucose concentrations. METHODS: Twenty-one healthy volunteers who represented all possible combinations of the two variant alleles were studied (genotypes CYP2C9*1/*1, *1/*2, *2/*2, *1/*3, *2/*3, and *3/*3 ). They received a single oral dose of 3.5 mg glyburide followed by 75 g glucose at 1, 4.5, and 8 hours after administration of glyburide. Glyburide was quantified in plasma by reversed-phase HPLC. Venous blood concentrations of glyburide, insulin, and glucose were analyzed with a population pharmacokinetic-pharmacodynamic model by use of NONMEM statistical software. RESULTS: Pharmacokinetics of glyburide depended significantly on CYP2C9 genotypes. In homozygous carriers of the genotype *3/*3, total oral clearance was less than half of that of the wild-type genotype *1/*1 (P <.001). Correspondingly, insulin secretion measured within 12 hours after glyburide ingestion was higher in carriers of the genotype *3/*3 compared with the other genotypes (P =.028), whereas the differences in glucose concentrations were not significant. CONCLUSIONS: Carriers of the CYP2C9 variant *3 had decreased oral clearances of glyburide. This confirms that glyburide is metabolized by CYP2C9. Corresponding differences in insulin plasma levels indicated that dose adjustment based on CYP2C9 genotype may improve antidiabetic treatment.     

Frequency of CYP2C9 variant alleles, including CYP2C9*13 in a Korean population and effect on glimepiride pharmacokinetics

What is known and Objective: Cytochrome P450 (CYP) 2C9 is a clinically important enzyme involved in the metabolism of many drugs commonly used in humans. Of several allelic variants known to affect the catalytic activity of the CYP2C9 enzyme, the frequencies of the CYP2C9*3 and CYP2C9*13 alleles in the Korean population have been reported as 1·1% and 0·6%, respectively. Our objective was to re‐evaluate the frequencies of CYP2C9 allelic variants in the Korean population, including the CYP2C9*13 allele by pyrosequencing, and to investigate the pharmacokinetics of glimepiride in relation to CYP2C9 genotypes, including CYP2C9*3/*3. Methods: 295 subjects were genotyped for CYP2C9*2 and CYP2C9*3 using the TaqMan procedure, and for CYP2C9*13 using pyrosequencing. These data were combined with our previously reported data to assess the CYP2C9 allele and genotype frequencies in 869 Korean subjects. Data from 24 of the 295 genotyped subjects (22 CYP2C9*1/*1 homozygotes, one CYP2C9*1/*3 heterozygote and one CYP2C9*3/*3 homozygote) who had participated in a bioequivalence study were analysed retrospectively to examine the effects of CYP2C9 genotype on glimepiride pharmacokinetics. Results: The frequencies of the CYP2C9*1/*3, *3/*3, and *1/*13 genotypes in the study population (n = 295) were 0·081 (n = 24), 0·010 (n = 3) and 0·003 (n = 1), respectively. In the 869 subjects from the combined studies, allele frequencies for CYP2C9*3 and CYP2C9*13 were 0·025 (95% CI: 0·018, 0·033) and 0·002 (95% CI: 0·000, 0·010), respectively. Relative to CYP2C9*1 homozygotes, the one CYP2C9*3 homozygous subject was found to have a higher AUC_0–∞ value (490% of the reference value) and a lower oral clearance rate (18% of the reference). What is new and Conclusion: This study is the first examination of CYP2C9*3 homozygotes in the Korean population. Our data on the one subject with this genotype suggest that CYP2C9*3/*3 momozygotes have lower clearance of glimepiride and are exposed to higher levels of the drug than wild‐type homozygotes. Although we identified a subject with the CYP2C9*13 allele using a new pyrosequencing assay, we were unfortunately unable to investigate its effects on glimepiride pharmacokinetics.     

CYP2C19 genetic mutations in North Indians

OBJECTIVES: To identify defective alleles of CYP2C19 (CYP2C19*2 and *3) in North Indians. METHODS: One hundred extensive metabolizers and 21 poor metabolizers of omeprazole were genotyped with respect to CYP2C19*2 and *3 alleles with polymerase chain reaction-based diagnostic tests. RESULTS: Fifty-two extensive metabolizers and six poor metabolizers were homozygous with the CYP2C19*1/*1 genotype, and 48 extensive metabolizers and six poor metabolizers were heterozygous with the CYP2C19*1/*2 genotype. Nine poor metabolizers were homozygous with the CYP2C19*2/*2 genotype. No extensive or poor metabolizers demonstrated the presence of the CYP2C19*3 allele. CYP2C19*2 could explain 43% (9/21) of the poor metabolizers and 57% (24/42) of the defective alleles in poor metabolizers. Allele frequency of CYP2C19*1 and *2 was 0.7 (95% confidence interval of 0.65 to 0.75) and 0.3 (95% confidence interval of 0.25 to 0.35), respectively. Homozygous extensive metabolizers excreted 7.85 +/- 7.6 micromol 5-hydroxyomeprazole in 8 hours, which was 28% more as compared with heterozygous extensive metabolizers who excreted 5.6 +/- 3.6 micromol 5-hydroxyomeprazole in 8 hours (P < .05). CONCLUSIONS: CYP2C19*2 demonstrated allele frequency of 0.3, whereas CYP2C19*3 was absent in North Indians. Because CYP2C19*2 is not able to explain 57% of poor metabolizers, other mutations (CYP2C19*4 to *8) might be present in North Indians. CYP2C19 demonstrated differential evolution in North Indians because the frequency of CYP2C19*2 was similar to that in Oriental subjects, but that of CYP2C19*3 was similar to that in white subjects.     

Pharmacokinetics of losartan and its metabolite E-3174 in relation to the CYP2C9 genotype

BACKGROUND AND AIM: Losartan is metabolized by polymorphic CYP2C9 to E-3174. Our aim was to evaluate the pharmacokinetics of losartan and E-3174 in relation to the CYP2C9 genotype. METHODS: A 50-mg oral dose of losartan was given to 22 Swedish volunteers with different CYP2C9 genotypes. Losartan and E-3174 were analyzed by HPLC in plasma and urine samples collected up to 24 hours after drug intake. Furthermore, losartan and E-3174 were analyzed in 8-hour urine samples collected from 17 Spanish subjects after a single oral dose of 25 mg losartan. RESULTS: The maximum plasma concentration of E-3174 was significantly (P <.05) lower in the CYP2C9*1/*3 (n = 5) and CYP2C9*2/*3 (n = 4) groups compared with the CYP2C9*1/*1 (n = 6) and CYP2C9*1/*2 (n = 3) groups and extremely low in 1 subject with the CYP2C9*3/*3 genotype. The ratio of the total losartan area under the plasma concentration-time curve (AUC) to the total E-3174 AUC (AUC(losartan)/AUC(E-3174)) was higher in the subject with the CYP2C9*3/*3 genotype (30-fold) and also in the CYP2C9*1/*3 and *2/*3 groups (approximately 2- and 3-fold, respectively) compared with the CYP2C9*1/*1 group. The plasma ratios correlated significantly with the 0- to 8-hour urinary losartan/E-3174 ratios. Among the total of 39 subjects, the urinary ratio was significantly higher in subjects with the CYP2C9*1/*3 (n = 10) and *2/*3 (n = 4) genotypes than in those with the CYP2C9*1/*1 genotype (n = 11; P <.01) and approximately 40-fold higher in subjects with the CYP2C9*3/*3 genotype (n = 3). CONCLUSION: The CYP2C9*3 allele was shown to be associated with decreased formation of E-3174 from losartan. The significant differences between genotypes in plasma and urine losartan/E-3174 ratios and the good correlation between the plasma and urine ratios suggest that the losartan/E-3174 ratio in 0- to 8-hour urine specimens may serve as a phenotyping assay for CYP2C9 activity. Further studies in larger populations will be required to establish this.     

高分辨熔解方法的建立及在真菌感染患者CYP2C19遗传多态性检测中的应用

目的 探讨高分辨熔解方法 (high resolution melting,HRM)检测真菌感染患者CYP2C19遗传多态性的可行性.方法 建立HRM方法 检测CYP2C19 * 2和CYP2C19 * 3两个多态性位点的基因型,并与传统方法 PCR-限制性片段长度多态性(PCR-RFLP)及序列分析结果 相比较,进一步应用于47例真菌感染患者基因型的检测与分析.结果 2种方法 检测CYP2C19 * 2和CYP2C19* 3基因型结果 完全一致,与DNA序列分析结果 也相吻合,而HRM方法 操作更为简便,耗时更短.47份临床标本检测结果 显示,CYP2C19的2个多态性位点存在不同基因型,CYP2C19 * 1/ * 1所占比例为48.9%(23/47),CYP2C19 * 1/ * 2为25.5%(12/47),CYP2C19 * 1/ * 3为6.4%(3/47),CYP2C19 * 2/ * 2为12.8%(6/47),CYP2C19 * 2/ * 3为6.4%(3/47).结论 HRM方法 能有效检测CYP2C19基因多态性,且较PCR-RFLP方法 更为简便、快速.此外,CYP2C19基因在真菌感染患者中存在明显的遗传多态性.     

Pharmacokinetics and toxicity of docetaxel: role of CYP3A, MDR1, and GST polymorphisms

OBJECTIVE: Patients initiating docetaxel chemotherapy were genotyped for CYP3A4, CYP3A5, MDR1, GSTM1, GSTT1, GSTM3, and GSTP1 to identify variability factors of docetaxel pharmacokinetics and toxicity. METHODS: Genotyping was performed by direct sequencing (CYP3A4), real-time polymerase chain reaction (CYP3A5), and polymerase chain reaction-restriction fragment length polymorphism (MDR1 and GST). The clearance and area under the curve of docetaxel were calculated by use of a Bayesian approach. Absolute neutrophil count was recorded twice weekly. RESULTS: With regard to the pharmacokinetic analysis, 58 patients were included. CYP3A4*1B carriers (*1A/*1B, n=4), who are also CYP3A5*1/*3 carriers, had a significantly higher clearance and lower dose-normalized area under the curve of docetaxel than those with the wild genotype (*1A/*1A, n=53): 55.2+/-13.5 L/h versus 37.3+/-11.7 L/h (P=.01) and 31.4+/-6.2 (microg . h/L)/(mg/m(2)) versus 52.7+/-18.2 (microg . h/L)/(mg/m(2)) (P=.005), respectively. No influence of MDR1 was evidenced. With regard to the pharmacodynamic analysis, febrile neutropenia occurred more frequently in GSTP1*A/*B carriers (31.6% versus 3.7% in *A/*A carriers and 0% in *A/*C, *B/*B, and *B/*C carriers) (P=.037). Grade 3 neutropenia occurred more frequently in 3435TT MDR1 genotype carriers: TT, 100%; CT, 77.3%; and CC, 54.5% (P=.046). No influence of GSTM1, GSTT1, or GSTM3 polymorphisms was evidenced on docetaxel toxicity. CONCLUSIONS: Patients carrying the CYP3A*1B allele may have enhanced docetaxel clearance and may be underexposed, whereas those carrying GSTP1*A/*B and 3435TT genotypes may have excessive hematologic toxicity. Further studies are warranted to determine the usefulness of genotyping before docetaxel treatment.