Genetic polymorphism of cytochrome P450s, CYP2C19, and CYP2C9 in a Japanese population

Genetic Polymorphisms of Cytochrome P450 2C19 in Functional Dyspeptic Patients Treated with Cimetidine

Inter-individual pharmacokinetic variation of H₂-receptor antagonist is related to genetic polymorphism of CYP2C19. We investigated the frequency of CYP2C19 genetic polymorphism and the treatment duration of cimetidine by CYP2C19 genotypes in functional dyspeptic patients without definite causes who were treated with cimetidine in Korea. One hundred subjects with functional dyspepsia participated in this study from March 1, 2010 to June 30, 2011. They were tested by upper gastrointestinal endoscopy and treated for their dyspepsia with cimetidine. The single nucleotide polymorphisms (SNPs) of CYP2C19 were genotyped using the Seeplex CYP2C19 ACE Genotyping system. There were no significant differences in the demographic, clinical, or laboratory findings among the CYP2C19 subgroups which are wild type homozygote (W/W), heterozygote (W/V), and variant homozygote (V/V). The frequencies of CYP2C19 subgroups were 33 (33%) in W/W, 49 (49%) in W/V, and 18 (18%) in V/V, respectively. The mean duration of cimetidine treatment (in weeks) was the shortest in the V/V among the CYP2C19 genotypes (W/W: 5.1±1.5, W/V: 4.0±1.7, V/V: 2.1±0.7; p<0.001). This study can also act as a basis for further investigation to identify the underlying genetic, epigenetic, or environmental factors in CYP2C19 enzyme activity.

Genetic polymorphisms and novel allelic variants of CYP2C19 in the Chinese Han population

Aim: This study aims to systematically investigate the genetic polymorphisms of the CYP2C19 gene and provide accurate data of the allele distribution pattern in the Chinese Han population. Materials & Methods: We amplified all nine exons of the CYP2C19 gene in 2127 unrelated healthy Chinese Han subjects from two geographical locations (Zhejiang province, n = 1127; Hebei province, n = 1000), using direct sequencing. Results: In total, six previously reported alleles were found in our study, in which two alleles CYP2C19*6 and CYP2C19*18 were reported for the first time in Chinese Han subjects. In addition, 35 novel variants were detected in the present work, which included 11 new named alleles, 12 nonsynonymous mutations and one insert variant. Conclusion: This study provides important data on the pattern of CYP2C19 polymorphisms in Chinese Han subjects, using the largest group of individuals. Furthermore, the study also detects the largest number of novel alleles in one population. These findings are of potential benefit to the development of personalized medicine for the Chinese Han population.

Original submitted 25 June 2012; Revision submitted 20 August 2012

Interethnic and Intraethnic Variability of CYP2C8 and CYP2C9 Polymorphisms in Healthy Individuals

Cytochrome P450 (CYP) superfamily members CYP2C8 and CYP2C9 are polymorphically expressed enzymes that are involved in the metabolic inactivation of several drugs, including, among others, antiepileptics, NSAIDs, oral hypoglycemics, and anticoagulants. Many of these drugs have a narrow therapeutic index, and growing evidence indicates a prominent role of CYP2C8 and CYP2C9 polymorphisms in the therapeutic efficacy and in the development of adverse effects among patients treated with drugs that are CYP2C8 or CYP2C9 substrates. In this review, we summarize present knowledge on human variability in the frequency of variant CYP2C8 and CYP2C9 alleles. Besides an expected interethnic variability in allele frequencies, a large intraethnic variability exists. Among Asian subjects, for example, statistically significant differences (p < 0.0001) in CYP2C9*3 allele frequencies between Chinese and Japanese individuals have been reported. In addition, individuals from East Asia present different allele frequencies for CYP2C9*2 and CYP2C9*3 compared with South Asian subjects (p < 0.0001). Among Caucasian Europeans, statistically significant differences for the frequency of CYP2C8*3, CYP2C9*2, and CYP2C9*3 exist (p < 0.0001). This indicates that Asian individuals or Caucasian European individuals cannot be considered as homogeneous groups regarding CYP2C8 or CYP2C9 allele frequencies. Caucasian American subjects also show a large variability in allele frequencies, which is likely to be related to ethnic ancestry. A higher frequency of variant CYP2C8 and CYP2C9 alleles is expected among Caucasian Americans with South European ancestry than in individuals with North European ancestry. The findings summarized in this review suggest that among individuals with Asian or European ancestry, intraethnic differences in the risk of developing adverse effects with drugs that are CYP2C8 or CYP2C9 substrates are to be expected. In addition, the observed intraethnic variability reinforces the need for proper selection of control subjects and points against the use of surrogate control groups for studies involving association of CYP2C8 or CYP2C9 alleles with adverse drug reactions or spontaneous diseases.

Randomised clinical trial: esomeprazole for the prevention of nonsteroidal anti-inflammatory drug-related peptic ulcers in Japanese patients

BACKGROUND

The use of proton pump inhibitors for prevention of nonsteroidal anti-inflammatory drug (NSAID)-induced gastrointestinal adverse events is well documented. However, data regarding the efficacy and safety of this approach in Japan are scarce.

AIM

To evaluate the efficacy and tolerability of esomeprazole in preventing NSAID-induced peptic ulcers in Japanese at-risk patients.

METHODS

Male and female Japanese adult patients (aged ≥ 20 years) with endoscopically confirmed history of peptic ulcers who required long-term oral NSAID therapy for a chronic inflammatory condition were randomised to 24 weeks' treatment with esomeprazole 20 mg once daily or matching placebo. The primary end point was the Kaplan-Meier estimated proportion of ulcer-free patients.

RESULTS

Overall, 343 patients were randomised to treatment (esomeprazole, n = 175; placebo, n = 168). The Kaplan-Meier estimated ulcer-free rate over the 24-week treatment period was significantly higher (log-rank P < 0.001) in esomeprazole-treated patients (96.0%; 95% CI 92.8, 99.1) than in placebo recipients (64.4%; 95% CI 56.8, 71.9). Esomeprazole was effective at preventing peptic ulcers in both Helicobacter pylori-positive and -negative patients (96.3% vs. 95.5% of patients ulcer-free, respectively); however, in the placebo group, the proportion of ulcer-free patients at 24 weeks was markedly lower among H. pylori-positive than -negative patients (59.7% vs. 69.9%). The NSAID type did not seem to affect the estimated ulcer-free rate with esomeprazole. Treatment with esomeprazole was well tolerated.

CONCLUSION

Esomeprazole 20 mg once daily is effective and safe in preventing ulcer recurrence in Japanese patients with a definite history of peptic ulcers who were taking an NSAID (ClinicalTrials.gov identifier: NCT00542789).

Initial voriconazole trough blood levels and clinical outcomes of invasive aspergillosis in patients with hematologic malignancies

There are limited data on the relationship between voriconazole levels and clinical outcomes relative to invasive aspergillosis (IA). We therefore analyzed the association between initial voriconazole trough blood levels and clinical responses of IA in patients with hematologic malignancies. All adult patients treated with voriconazole in a tertiary care hospital in Seoul, South Korea, between August 2009 and April 2011 were identified from pharmacy records. Initial voriconazole trough levels were routinely measured 1 week after therapy and patient responses were classified as success (complete or partial response) or failure (stable response, progression of disease, or death) at 2 weeks post-therapy. Fifty-two patients, involving 2 (4%) proven, 29 (56%) probable, and 21 (40%) possible IA infections, were included. Of these, 11 (21%) had initial voriconazole levels of ≤ 2 mg/l and the remaining 41 (79%) had > 2 mg/l. There were slightly fewer successful responses (45%, 5/11) in the patients with initial voriconazole levels ≤ 2 mg/l than in those with voriconazole levels > 2 mg/l (51%, 21/41), but the difference was not statistically significant (P= 0.73). Neutropenia (OR 0.1, P= 0.008) and immunosuppression (OR 0.1, P= 0.004) were independently associated with 2-week successful response after voriconazole therapy. In conclusion, initial voriconazole trough levels may not significantly affect clinical outcomes of IA at 2 weeks after voriconazole therapy in patients with hematologic malignancies. Further studies of prospective design are needed to establish the optimal procedure for voriconazole drug monitoring.

Specific safety and tolerability considerations in the use of anticonvulsant medications in children

Epilepsy is one of the most common neurological disorders in the pediatric age range, and the majority of affected children can be safely and effectively treated with antiepileptic medication. While there are many antiepileptic agents on the market, specific drugs may be more efficacious for certain seizure types or electroclinical syndromes. Furthermore, certain adverse effects are more common with specific classes of medication. Additionally patient-specific factors, such as age, race, other medical conditions, or concurrent medication use may result in higher rates of side effects or altered efficacy. Significant developmental changes in gastric absorption, protein binding, hepatic metabolism, and renal clearance are seen over the pediatric age range, which impact pharmacokinetics. Such changes must be considered to determine optimal dosing and dosing intervals for children at specific ages. Furthermore, approximately one third of children require polytherapy for seizure control, and many more take concurrent medications for other conditions. In such children, drug–drug interactions must be considered to minimize adverse effects and improve efficacy. This review will address issues of antiepileptic drug efficacy, tolerability and ease of use, pharmacokinetics, and drug–drug interactions in the pediatric age range.

Allele and genotype frequencies of CYP2C9 within an Iranian population (Mazandaran)

Cytochrome P450 2C9 (CYP2C9) is a polymorphic enzyme responsible for the metabolism of different drugs, some with low therapeutic index. The frequency of functionally important mutations and alleles of the gene coding for CYP2C9 shows wide ethnic variations. The present study aimed to determine the prevalence of the most common allelic variants of the CYP2C9 enzyme and to predict the genotype frequency in the Mazandarani ethnic group among the Iranian population. Genotyping of CYP2C9 allelic variants was carried out in 103 unrelated subjects by polymerase chain reaction and restriction fragment length pattern analysis. The frequencies for CYP2C9 alleles *1, *2, and *3 were 78%, 12%, and 10%, respectively. No subjects were found carrying the CYP2C19*11 allele. The frequencies of CYP2C9 genotypes *1/*1, *1/*2, *1/*3, *2/*2, *2/*3, and *3/*3 were 61%, 19%, 16%, 1.5%, 2.5%, and 0.0%, respectively. The result of the present study showed that the two inactive alleles of CYP2C9 accounted for 22% of CYP2C9 alleles in our sample versus 1.5%-29% reported in other populations. The frequencies of the studied alleles resulted in significant differences between our sample and African and Eastern Asian populations.

CYP4F2 gene polymorphism as a contributor to warfarin maintenance dose in Japanese subjects

WHAT IS KNOWN AND OBJECTIVE

Polymorphisms in the gene encoding CYP4F2 may partly explain the variability in warfarin maintenance dose by altering the metabolism of vitamin K. To determine the genetic factors that cause large inter-patient variability in warfarin efficacy, we investigated the relationship between serum warfarin concentration and CYP4F2 V433M (1347C>T, rs2108622) polymorphism in Japanese subjects.

METHODS

Gene variations in VKORC1, CYP2C9 and CYP4F2 were analysed in 126 Japanese patients treated with warfarin. The daily dosage of warfarin, concentration of S- and R-warfarin in plasma, and prothrombin time international normalized ratio (PT-INR) was used as the pharmacokinetic and pharmacodynamic indices.

RESULTS AND DISCUSSION

The maintenance dose of warfarin was larger in the CYP4F2 1347 CT genotype group (3·59±1·80 mg/day, P=0·027) than in the CYP4F2 CC genotype group (2·88±1·00 mg/day). CYP4F2 1347C>T polymorphism significantly affected serum R-warfarin concentration when the VKORC1-1639 genotypes are AG and GG.

WHAT IS NEW AND CONCLUSION

Although a significant inter-patient difference in warfarin maintenance dose was observed between the CYP4F2 CC and CT genotypes, serum S-warfarin concentration was not significantly different between them. An effect of CYP4F2 V433M polymorphism on warfarin maintenance dose was observed but was relatively small when compared to the effects of CYP2C9 and VKOR polymorphism.

CYP2C9 polymorphism in patients with epilepsy: genotypic frequency analyzes and phenytoin adverse reactions correlation

OBJECTIVE

CYP2C9 is a major enzyme in human drug metabolism and the polymorphism observed in the corresponding gene may affect therapeutic outcome during treatment. The distribution of variant CYP2C9 alleles and prevalence of phenytoin adverse reactions were hereby investigated in a population of patients diagnosed with epilepsy.

METHOD

Allele-specific PCR analysis was carried out in order to determine frequencies of the two most common variant alleles, CYP2C9*2 and CYP2C9*3 in genomic DNA isolated from 100 epileptic patients. We also analyzed the frequency of phenytoin adverse reactions among those different genotypes groups. The data was presented as mean±standard deviation.

RESULTS

The mean age at enrollment was 39.6±10.3 years (range, 17-72 years) and duration of epilepsy was 26.5±11.9 years (range 3-48 years). The mean age at epilepsy onset was 13.1±12.4 years (range, 1 month-62 years). Frequencies of CYP2C9*1 (84%), CYP2C9*2 (9%) and CYP2C9*3 (7%) were similar to other published reports. Phenytoin adverse reactions were usually mild and occurred in 15% patients, without correlation with the CYP2C9 polymorphism (p=0.34).

CONCLUSION

Our findings indicate an overall similar distribution of the CYP2C9 alleles in a population of patients diagnosed with epilepsy in the South of Brazil, compared to other samples. This sample of phenytoin users showed no drug related adverse reactions and CYP2C9 allele type correlation. The role of CYP2C9 polymorphism influence on phenytoin adverse reaction remains to be determined since some literature evidence and our data found negative results.

Vitamin K antagonists in children with heart disease: height and VKORC1 genotype are the main determinants of the warfarin dose requirement

Managing vitamin K antagonist (VKA) therapy is challenging in children because of a narrow therapeutic range and wide inter- and intra-individual variability in dose response. Only a few small studies have investigated the effect of nongenetic and genetic factors on the dose response to VKAs in children. In a cohort study including 118 children (median age 9 years; range, 3 months-18 years) mostly with cardiac disease, we evaluated by multivariate analysis the relative contribution of nongenetic factors and VKORC1/CYP2C9/CYP4F2 genotypes on warfarin (n = 83) or fluindione (n = 35) maintenance dose and the influence of these factors on the time spent within/above/below the range. The results showed that height, target international normalized ratio and VKORC1 and CYP2C9 genotypes were the main determinants of warfarin dose requirement, accounting for 48.1%, 4.4%, 18.2%, and 2.0% of variability, respectively, and explaining 69.7% of the variability. Our model predicted the warfarin dose within 7 mg/wk in 86.7% of patients. None of the covariates was associated with the time spent above or below the international normalized ratio range. Whether this model predicts accurately the effective maintenance dose is currently being investigated.

Population differences in major functional polymorphisms of pharmacokinetics/pharmacodynamics-related genes in Eastern Asians and Europeans: implications in the clinical trials for novel drug development

Drug lag, recently discussed extensively in Japan, can be divided into two phases: clinical development time and application review time. The former factor is still an important problem that might be improved by promoting multi-regional clinical trials and considering the results from other similar populations with Japanese, such as Koreans and Chinese. In this review, we compare the allelic or genotype frequencies of 30 relatively common functional alleles mainly between Eastern Asians and Europeans as well as among 3 major populations in Eastern Asian countries, Japan, Korea, and China, in 12 pharmacokinetics (PK)/pharmacodynamics (PD)-related genes; CYP2C9 (*2 and *3), CYP2C19 (*2, *3 and *17), 13 CYP2D6 haplotypes including *4, *5 and *10, CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5, *6 and *7), GSTM1 and GSTT1 null genotypes, SLCO1B1 521T>C, ABCG2 421C>A, and HLA-A*31:01 and HLA-B*58:01. In this review, differences in allele frequencies (AFs) or genotype frequencies (GFs) less than 0.1 (in the cases of highest AF (GF) ≥0.1) or less than 0.05 (in the cases of lowest AF (GF) <0.1) were regarded as similar. Between Eastern Asians and Europeans, AFs (or GFs) are regarded as being different for many alleles such as CYP2C9 (*2), CYP2C19 (*2, *3 and *17), CYP2D6 (*4 and *10), CYP3A5 (*3), UGT1A1 (*28 and *6), NAT2 (*5*7), GSTT1 null and ABCG2 421C>A. Among the 3 Eastern Asian populations, however, only AFs of CYP2C19*3, CYP2D6*10, HLA-A*31:01 and HLA-B*58:01 are regarded as dissimilar. For CYP2C19*3, the total functional impact on CYP2C19 could be small if the frequencies of the two null alleles CYP2C19*2 and *3 are combined. Regarding CYP2D6*10, frequency difference over 0.1 is observed only between Japanese and Chinese (0.147). Although environmental factors should be considered for PK/PD differences, we could propose that among Japan, Korea, and China, genetic differences are very small for the analyzed common PK-related gene polymorphisms. On the other hand, AFs of the two HLA alleles important for cutaneous adverse drug reactions are diverse even among Eastern Asians and thus should be taken into account.

In vitro assessment of the allelic variants of cytochrome P450

The cytochrome P450 (CYP) superfamily is one of the most important groups of enzymes involved in drug metabolism. It is responsible for the metabolism of a large number of drugs. Many CYP isoforms are expressed polymorphically, and catalytic alterations of allelic variant proteins can affect the metabolic activities of many drugs. The CYP2D6, CYP2C9, CYP2C19, and CYP2B6 genes are particularly polymorphic, whereas CYP1A1, CYP1A2, CYP2E1, and CYP3A4 are relatively well conserved without common functional polymorphisms. In vitro studies using cDNA expression systems are useful tools for evaluating functional alterations of the allelic variants of CYP, particularly for low-frequency alleles. Recombinant CYPs have been successfully expressed in bacteria, yeast, baculoviruses, and several mammalian cells. Determination of CYP variant-mediated kinetic parameters (Km and Vmax) in vitro can be useful for predicting drug dosing and clearance in humans. This review focuses on the advantages and disadvantages of the various cDNA-expression systems used to determine the kinetic parameters for CYP allelic variants, the methods for determining the kinetic parameters, and the findings of in vitro studies on highly polymorphic CYPs, including CYP2D6, CYP2C9, CYP2C19, and CYP2B6.

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Effect of cytochrome P450 2C19 genotype on voriconazole exposure in cystic fibrosis lung transplant patients

PURPOSE

Voriconazole is widely used to treat invasive aspergillosis after lung transplantation. In cystic fibrosis patients, the interindividual variability in drug disposition complicates the optimal voriconazole dosing and increases the risk of toxicity. The objective of this retrospective study was to evaluate the influence of CYP2C19 genotype on voriconazole response in lung transplant patients with cystic fibrosis.

METHODS

We retrospectively studied 24 Caucasian cystic fibrosis lung transplant recipients who received voriconazole. We analyzed the influence of CYP2C19 genotype (*2 and *17 alleles) on voriconazole exposure and maintenance dose and side effects.

RESULTS

Heterozygous carriers of the CYP2C19*2-deficient allele required lower maintenance doses (440 ± 107 mg/day) compared with wild-type and CYP2C19*17-allele carriers (633 ± 197 mg/day and 600 ± 193 mg/day, respectively, P<0.05). The time to achieve the therapeutic range and the proportion of out-of-range concentrations were significantly higher in the CYP2C19*2 group (31.3% vs. 12.1% and 9.8% of above-range levels in the CYP2C19*1 and CYP2C19*17 groups, respectively) or CYP2C19*17 group (37.9% vs. 15.6% and 13% of below-range levels in the CYP2C19*1 and CYP2C19*2 groups, respectively) (P<0.01). No relationship was found between voriconazole toxicity and CYP2C19 status.

CONCLUSIONS

In this frail population, voriconazole exposure is strongly influenced by CYP2C19 genotype, and determining the genotype before voriconazole initiation may help determine the initial dosing regimen that will promptly achieve therapeutic plasma levels without producing out-of-range levels.

VKORC1-1639G>A, CYP2C9, EPHX1691A>G genotype, body weight, and age are important predictors for warfarin maintenance doses in patients with mechanical heart valve prostheses in southwest China

OBJECTIVE

To investigate the contribution of genetic polymorphisms of vitamin K epoxide reductase complex subunit 1 gene VKORC1-1639G>A, cytochrome P450 2C9 gene (CYP2C9), EPHXI, and clinical factors to warfarin sensitivity in southwest Chinese Han patients with mechanical heart valve prostheses.

METHODS

A total of 127 patients with mechanical heart valve prostheses who have been followed up at our department during the past 23 years were enrolled in this study and compared to a control group that consisted of 133 randomly selected healthy blood donors. These Chinese patients met stable warfarin dosage requirements and had reached the target international normalized ratio (INR) of 1.5-2.0. PCR and direct sequencing were carried out to identify the polymorphisms of VKORC1-1639G>A (rs9923231), CYP2C9*3 (rs1057910), CYP2C9 IVS3-65G>C (rs9332127), and EPHX1691A>G (rs4653436). In addition, total and free (non-protein-bound) warfarin concentrations were analyzed.

RESULTS AND CONCLUSIONS

There were great interindividual differences in warfarin maintenance dosage (ranging from 0.6 to 8.4 mg/day) among the 127 patients with mechanical heart valve prostheses. VKORC1-1639G>A, CYP2C9, EPHX1691A>G polymorphism, body weight, and age were found to affect the dose demands. Multiple linear regression models incorporating genetic polymorphisms of VKORC1, CYP2C9, EPHX1691A>G, and the nongenetic factors of age and body weight were developed, and explained up to 76.8% of the total variation (adjusted R (2) of 0.743) in warfarin maintenance doses in southwest Chinese patients with mechanical heart valve prostheses.

Intravenous micafungin versus voriconazole for chronic pulmonary aspergillosis: a multicenter trial in Japan

Chronic pulmonary aspergillosis (CPA) is slowly progressive inflammatory pulmonary syndrome due to Aspergillus spp. The evidence regarding CPA treatment is limited. We conducted a randomized, multicenter, open-label trial comparing intravenous micafungin (MCFG) of 150-300 mg once daily with intravenous voriconazole (VRCZ) of 6 mg/kg twice on Day 1 followed by 4 mg/kg twice daily for the treatment of 107 in patients with CPA to compare the efficacy and safety of both drugs as initial treatment in Japan. Treatment effectiveness was defined by clinical, mycological, radiological and serological responses 2 weeks after the initial administration and at the end of therapy. The total of 50 and 47 patients were assigned to the MCFG and VRCZ groups, respectively. The difference in efficacy rates between MCFG and VRCZ was not significant, either after 2 weeks [68.0% vs. 58.7%; the absolute difference, 9.3% with a 95% confidence interval (CI), -9.97 to 28.58, P = 0.344] or at the end of therapy (60.0% vs. 53.2%; the absolute difference, 6.8% with a 95% CI, -12.92 to 26.54, P = 0.499). In the safety evaluation, fewer adverse events occurred in the MCFG than VRCZ group (26.4% vs. 61.1%, P = 0.0004). MCFG was as effective as VRCZ and significantly safer than as an initial treatment of CPA. (UMIN Clinical Trials Registry number, UMIN000001786.).

Relationship between the Acid-Inhibitory Effects of Two Proton Pump Inhibitors and CYP2C19 Genotype in Japanese Subjects: A Randomized Two-Way Crossover Study

This two-way crossover study investigated possible differences between the proton pump inhibitors, omeprazole and rabeprazole, in their effect on gastric acid secretion in Japanese subjects with differing cytochrome P450, family 2, subfamily C, polypeptide 19 (CYP2C19) genotypes. A total of 23 Helicobacter pylori-negative healthy volunteers received omeprazole 20 mg/day and rabeprazole 10 mg/day. Each drug treatment was given for a continuous 7-day period allocated in random order, with an interval of at least 1 week between drug treatment periods to allow for wash-out. Intragastric pH was measured on days 1 and 7. Overall median intragastric pH levels at 7 and 8 h after the first administration were significantly higher with omeprazole. There was no significant difference in intragastric pH in homozygous extensive metabolizers, whereas intragastric pH was significantly higher with omeprazole in combined data from heterozygous extensive metabolizers and poor metabolizers at 6, 7 and 8 h after the first drug administration. There were no significant differences in intragastric pH between omeprazole and rabeprazole irrespective of genotype on day 7 of administration. In conclusion, on day 1 the time to onset of the antisecretory action of 20 mg/day omeprazole was more rapid than that of 10 mg/day rabeprazole in Japanese individuals who have a higher incidence of the CYP2C19 poor metabolizer genotype, however by day 7 no difference in antisecretory effect was found, regardless of genotype.

Implementing genotype-guided antithrombotic therapy

Genotyping has the potential to improve the efficacy and safety of major antithrombotic drugs. For warfarin, the stable maintenance dose varies from 1-10 mg/day. The VKORC1 -1639G>A allele and the CYP2C9*2 and *3 alleles (cumulative frequency: 90% in Asians, 65% in Europeans and 20% in Africans), explain 45% of response variability in European and 30% in African populations. The large clinical trials COAG and EU-PACT will define the extent to which pharmacogenetic dosing affects the safety and efficacy of warfarin and coumarin derivatives. The platelet inhibitor clopidogrel requires activation by the CYP2C19 enzyme. CYP2C19*2 and *3 alleles (cumulative frequency: 20-50%) produce null enzyme activity, and their presence attenuates platelet inhibition and increases cardiovascular events. The US FDA-mandated drug labeling recognizes the relevance of genotyping in the selection and dosing of both warfarin and clopidogrel.

Patterns of pharmacogenetic diversity in African populations: role of ancient and recent history

AIMS

The knowledge that genetic variation influencing drug response is clearly structured among human populations has prompted many studies aimed at obtaining pharmacogenetic profiles in specific populations. While large amounts of data are being produced for populations from developed countries, the African continent still remains very poorly studied. To help to fill this gap, this work characterized three previously uncharacterized African populations for a set of pharmacogenetically relevant polymorphisms.

MATERIALS & METHODS

Seven polymorphic variations in four genes that encode enzymes from phase I (CYP2C9, CYP3A4 and CYP3A5) or phase III (ABCB1) of drug metabolism were analyzed in population samples from Cabinda (n = 107), Mozambique (n = 109) and São Tomé e Príncipe (n = 126). All three populations shared strong recent historical links with Portugal.

RESULTS

The majority of the screened variations displayed large contrasts in allele frequencies between European and African populations, and this study identified a substantial higher European influence in São Tomé e Príncipe than in Cabinda or Mozambique. Admixture analysis demonstrated that the European contribution to the population of São Tomé e Príncipe amounted to 13.3 +/- 3.3%. Furthermore, the proportion of African or European pharmacogenetic ancestry varied widely across each São Tomean individual.

DISCUSSION & CONCLUSION

This implies that genetic association studies conducted in São Tomé e Príncipe should take into account the confounding factor of admixture to avoid spurious positive or negative results. Our findings also indicate that drug dosage requirements may be different in São Tomé e Príncipe than in other African populations. Thus, the search for pharmacogenetic risk factors should be assessed at an individual level, therefore fulfilling the perspective of personalized medicine. This study further indicates that the common notion of 'African population' might hide a pattern of pharmacogenetic heterogeneity whose real extent still needs to be evaluated by means of a refined sampling of the entire continent.

Polymorphisms of human cytochrome P450 2C9 and the functional relevance

Human cytochrome P450 2C9 (CYP2C9) accounts for ∼20% of hepatic total CYP content and metabolizes ~15% clinical drugs such as phenytoin, S-warfarin, tolbutamide, losartan, and many nonsteroidal anti-inflammatory agents (NSAIDs). CYP2C9 is highly polymorphic, with at least 33 variants of CYP2C9 (*1B through *34) being identified so far. CYP2C9*2 is frequent among Caucasians with ~1% of the population being homozygous carriers and 22% are heterozygous. The corresponding figures for the CYP2C9*3 allele are 0.4% and 15%, respectively. There are a number of clinical studies addressing the impact of CYP2C9 polymorphisms on the clearance and/or therapeutic response of therapeutic drugs. These studies have highlighted the importance of the CYP2C9*2 and *3 alleles as a determining factor for drug clearance and drug response. The CYP2C9 polymorphisms are relevant for the efficacy and adverse effects of numerous NSAIDs, sulfonylurea antidiabetic drugs and, most critically, oral anticoagulants belonging to the class of vitamin K epoxide reductase inhibitors. Warfarin has served as a practical example of how pharmacogenetics can be utilized to achieve maximum efficacy and minimum toxicity. For many of these drugs, a clear gene-dose and gene-effect relationship has been observed in patients. In this regard, CYP2C9 alleles can be considered as a useful biomarker in monitoring drug response and adverse effects. Genetic testing of CYP2C9 is expected to play a role in predicting drug clearance and conducting individualized pharmacotherapy. However, prospective clinical studies with large samples are warranted to establish gene-dose and gene-effect relationships for CYP2C9 and its substrate drugs.

Correlation between voriconazole trough plasma concentration and hepatotoxicity in patients with different CYP2C19 genotypes

Voriconazole metabolism is mostly mediated via the cytochrome P450 (CYP) 2C19 isozyme. The non-wild (mutant) type of CYP2C19 is generally found in 60-70% of Asian populations. Because the voriconazole trough plasma concentration has been reported to correlate with hepatotoxicity, this study investigated the effect of CYP2C19 polymorphism on the relationship between voriconazole trough concentrations and liver function abnormalities in 29 Japanese patients with fungal infections (CYP2C19 wild-type, n=10; non-wild-type, n=19). Hepatotoxicity, defined as liver enzyme abnormality according to the National Cancer Institute criteria, was observed in 10 (34.5%) of 29 patients with a trough concentration > or = 3.9 mg/L. Logistic regression analysis suggested that the therapeutic range for the voriconazole trough concentration should be 2-4 mg/L. Non-linear pharmacokinetic analysis suggested that voriconazole therapy should be initiated with a dose of 7.2-8.9 mg/kg/day for CYP2C19 wild-type and 4.4-6.5mg/kg/day for the non-wild-type in Japanese patients. These recommended initial dosages and subsequent dose adjustment for the target concentration range by therapeutic drug monitoring should avoid adverse events and thus enable continued effective voriconazole therapy for Japanese patients with mycoses.

Antibodies as a probe in cytochrome P450 research

Cytochrome P450 (P450) is the superfamily of enzymes responsible for biotransformation of endobiotics and xenobiotics. However, their large isoform multiplicity, inducibility, diverse structure, widespread distribution, polymorphic expression, and broad overlapping substrate specificity make it difficult to measure the precise role of each individual P450 to the metabolism of drugs (or carcinogens) and hamper the understanding of the relationship between the genetic/environmental factors that regulate P450 phenotype and the responses of the individual P450s to drugs. The antibodies against P450s have been useful tools for the quantitative determination of expression level and contribution of the epitope-specific P450 to the metabolism of a drug or carcinogen substrate in tissues containing multiple P450 isoforms and for implications in pharmacogenetics and human risk assessment. In particular, the inhibitory antibodies are uniquely suited for reaction phenotyping that helps to predict human pharmacokinetics for clinical drug-drug interaction potential in drug discovery and development.

Relative roles of CYP2C19 and CYP3A4/5 in midazolam 1′-hydroxylation

1. During the characterization of recombinant CYP2C19, it was observed that this enzyme metabolized midazolam, which is generally regarded as CYP3A4/5 substrate, and we therefore decided to pursue this observation further. 2. CYP2C19 showed a Michaelis-Menten pattern for midazolam 1'-hydroxylation and was inhibited by (+)-N-3-benzylnirvanol and S-mephenytoin, which are a standard potent inhibitor and a substrate of CYP2C19, respectively. 3. The inhibitory potency by CYP3A4/5 inhibitor on the midazolam 1'-hydroxylation in human liver microsomes (HLM) was correlated with the CYP3A4/5 specific catalytic activity, but such correlation was not observed in CYP2C19 enzyme. The in vitro intrinsic clearance value for midazolam 1'-hydroxylation was not changed by the addition of (+)-N-3-benzylnirvanol in four individual HLM preparations. 4. These results indicated that although CYP2C19 is capable of catalyzing midazolam 1'-hydroxylation, CYP3A4/5 play a more important role.

Approach to the prediction of the contribution of major cytochrome P450 enzymes to drug metabolism in the early drug-discovery stage

It is important to determine the cytochrome P450 (CYP) contribution of certain drugs by taking into consideration the attrition due to issues such as genetic polymorphism and inter-individual variation. In many cases in the early discovery stage, the metabolites of a new chemical have not been identified. Therefore, the present paper devised an approach in which the in vitro intrinsic clearance (CLint) value for new chemicals was determined by measuring substrate depletion. The following prediction methods were compared to calculate CLint using data from recombinant CYP enzymes: (1) the relative CYP content in human liver microsomes; (2) the relative activity factor (RAF) based on the Vmax value; and (3) the RAF value based on the CLint value. The most accurate prediction method was RAF based on CLint. This method would be useful in the early drug-discovery process in cases in which the main metabolite is not identified.

Genetic factors contribute to patient-specific warfarin dose for Han Chinese

BACKGROUND

Warfarin is a commonly prescribed anticoagulant drug for the prevention of thromboses. To address the association of genetic factors and warfarin dosage for ethnic Han Chinese, we genotyped six candidate genes involved in the warfarin interactive pathway with focus on SNPs with reported association with warfarin dose.

METHODS

We recruited a study population consisted of 318 patients receiving warfarin treatment and 995 healthy controls. PCR and direct sequencing were used to identify the sequence polymorphisms.

RESULTS

In our study population, SNP rs1799853 of CYP2C9, rs1687390 of ORM1-2, and rs2069919 of PROC showed no variation. SNPs rs12714145 of GGCX and rs1799809 of PROC showed no significant correlation with warfarin dose. The associations of SNPs rs9934438 and rs9923231 of VKORC1, the 3 (rs1057910) and C(-65) (rs9332127) alleles of CYP2C9, and SNP rs4653436 of EPHXI with the dose of warfarin were significant.

CONCLUSION

A multiple regression model based on the genetic polymorphisms of VKORC1, CYP2C9, EPHX1 and the non-genetic factors of age and body weight can explain 40.2% of the variance in warfarin dose in Han Chinese patients. Translation of this knowledge into clinical guidelines for warfarin prescription may improve the safety and efficacy of warfarin treatment among Han Chinese.

Pharmacogenetically relevant polymorphisms in Portugal

OBJECTIVE

Most drugs are developed based on data from European-derived 'reference' populations; however, clinically relevant DNA polymorphisms often demonstrate population-specific patterns of allele frequencies. Given that the knowledge of the frequency distribution of functional polymorphisms in a population may guide national planning for selection of therapeutic options, in the present study we examined the allele frequencies of enzymes responsible for drug disposition in Portugal.

PATIENTS & METHODS

Using PCR- and Pyrosequencing-based methods, the current study assessed the frequencies of 15 key polymorphisms from genes encoding enzymes involved in Phases I, II and III of drug metabolism, DNA repair and intracellular metabolism in 135 healthy individuals from Portugal.

RESULTS

Allele frequencies were derived for cytochrome P450 (CYP)2C9*2 (13.2%), CYP2C9*3 (8%), CYP2C19*2 (14%), CYP3A4*1B (7%), CYP3A5*3C (87.5%), glutathione S-transferase (GST)M1*0 (77.9%), GSTP1 313A>G (33%), inosine triphosphatase 94C>A (7%), UDP-glucuronosyltransferase (UGT)1A1*28 (28%), UGT1A1 -3156G>A (23%), ATP-binding cassette (ABC)B1 1236C>T (46%), ABCB1 2677G>A/T (2 and 42%), ABCG2 421C>A (8%), excision repair cross-complementing rodent repair deficiency 2 2251A>C (3%) and thymidylate synthetase 1494del (31%).

CONCLUSION

Although, on the whole, the frequency distributions among the Portuguese fitted the patterns commonly found in other Europeans well, evidence for some degree of African influence was observed. This is the most comprehensive study on pharmacogenetically relevant variations in Portugal to date, and the baseline of pharmacogenetic data might be important for determining policy guidelines for cancer prevention and drug treatments in the Portuguese population.

Reaction phenotyping: current industry efforts to identify enzymes responsible for metabolizing drug candidates

Reaction phenotyping studies to identify specific enzymes involved in the metabolism of drug candidates are increasingly important in drug discovery efforts. Experimental approaches used for CYP reaction phenotyping include incubations with cDNA expressed CYP enzyme systems and incubations containing specific CYP enzyme inhibitors. Since both types of experiments present specific advantages as well as known drawbacks, these studies are generally viewed as complementary approaches. Although glucuronidation pathways are also known to present potential drug-drug interaction issues as well as challenges related to their polymorphic expression, reaction phenotyping approaches for glucuronidation are generally limited to cDNA expressed systems due to lack of availability of specific UGT inhibitors. This article presents a limited review of current approaches to reaction phenotyping studies used within the pharmaceutical industry.

Limited frequency of the CYP2C19*17 allele and its minor role in a Japanese population

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

A novel CYP2C19 gene variant, CYP2C19*17, is associated with increased metabolic activity. Ethnic differences in the frequency of the variant allele have been reported. However, the frequency of the CYP2C19*17 allele has not been studied in the Japanese population.

WHAT THIS STUDY ADDS

In a population of 265 healthy Japanese subjects, a low frequency (1.3%) of the CYP2C19*17 allele was observed. The limited frequency of the *17 allele and the absence of a subject homozygous for *17 indicated that CYP2C19*17 would play a minor role in a Japanese population.

AIMS

We investigated the CYP2C19*17 allelic frequency in Japanese subjects, and evaluated whether CYP2C19*17 is an important determinant of interindividual variability of CYP2C19 activity.

METHODS

We enrolled 265 subjects to determine their CYP2C19 genotype and plasma metabolic ratio following a single dose of 40 mg omeprazole.

RESULTS

Seven subjects heterozygous for CYP2C19*17 and no *17/*17 subjects resulted in the CYP2C19*17 frequency being 1.3%. These heterozygotes had moderate metabolic activities when compared with the metabolic ratio of the other subjects.

CONCLUSIONS

The low frequency of CYP2C19*17 and the absence of *17/*17 indicates that CYP2C19*17 plays a minor role in the Japanese population.

Factors affecting the interindividual variability of warfarin dose requirement in adult Korean patients

INTRODUCTION

Warfarin, a commonly prescribed anticoagulant, exhibits large interindividual and interethnic differences in the dose required for its anticoagulation effect. Asian patients require a much lower maintenance dose compared with Caucasians; the explanation for these differences remains unknown.

METHODS

We analyzed five single nucleotide polymorphisms of the vitamin K epoxide reductase complex subunit 1 gene (VKORC1) and the *3 variant of cytochrome P450 (CYP)2C9, as well as the plasma warfarin concentration, in 108 Korean patients with atrial fibrillation.

RESULTS

Genotypic frequencies of VKORC1 +1173CT and CYP2C9*1/*3 were 17.6 and 10.2%, respectively, in the study population; VKORC1 +1173CC and CYP2C9*3/*4 were detected in one patient each. Patients carrying at least one copy of the VKORC1 +1173C allele, or the H7 (group B) haplotype, required a significantly higher warfarin dose (n = 20; 5.5 +/- 1.7 mg/day) than those homozygous for the +1173T allele, or the H1 (group A) haplotype, (3.8 +/- 1.2 mg/day; p < 0.001). There were statistically significant differences in warfarin dose between the CYP2C9*1/*1 (4.3 +/- 1.6 mg/day; p < 0.001) and those with the other two genotypes including CYP2C9*1/*3 and CYP2C9*3/*4 (2.7 +/- 0.9 mg/day). The multiple regression analysis revealed that the VKORC1 genotype (r2 = 0.197; p < 0.001), the age when warfarin started (r2 = 0.09; p < 0.001), body surface area (r2 = 0.041; p = 0.004) and CYP2C9 genotype (r2 = 0.029; p = 0.014) were factors associated with the daily dose of warfarin required.

CONCLUSION

In the present study, we found that the VKORC1 polymorphism had a dominant genetic influence on interindividual variability for warfarin dose in Korean patients. It explained approximately 32% of the overall variability in warfarin dose requirements given all of the variables studied. Thus, analysis of the VKORC1 genotypes may be important to guide warfarin dose selection and allow personalized warfarin treatment.

Characterization of Human Cytochrome P450 Enzymes Involved in the Metabolism of Cilostazol

Cilostazol (OPC-13013; 6-[4-(1-cyclohexl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-2(1H)-quinolinone) is widely used as an antiplatelet vasodilator agent. In vitro, the hydroxylation of the quinone moiety of cilostazol to OPC-13326 [6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3,4-dihydro-4-hydroxy-2(1H)-quinolinone], is the predominant route, and the hydroxylation of the hexane moiety to OPC-13217 is the second most predominant route. This study was carried out to identify and kinetically characterize the human cytochrome P450 (P450) isozymes responsible for the formation of the two major metabolites of cilostazol, namely, OPC-13326 and OPC-13217 [3,4-dihydro-6-[4-[1-(cis-4-hydroxycyclohexyl)-1H-tetrazol-5-yl)butoxy]-2(1H)-quinolinone)]. In in vitro studies using 14 recombinant human P450 isozymes, CYP1A1, CYP1A2, CYP1B1, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP2J2, CYP3A4, CYP3A5, and CYP4A11, cilostazol was metabolized to OPC-13326 mainly by CYP3A4 (K(m) = 5.26 muM, intrinsic clearance (CL(int)) = 0.34 microl/pmol P450/min), CYP1B1 (K(m) = 11.2 microM, CL(int) = 0.03 microl/pmol P450/min), and CYP3A5 (K(m) = 2.89 microM, CL(int) = 0.05 microl/pmol P450/min) and to OPC-13217 mainly by CYP3A5 (K(m) = 1.60 microM, CL(int) = 0.57 microl/pmol P450/min), CYP2C19 (K(m) = 5.95 microM, CL(int) = 0.16 microl/pmol P450/min), CYP3A4 (K(m) = 5.35 microM, CL(int) = 0.10 microl/pmol P450/min), and CYP2C8 (K(m) = 33.8 microM, CL(int) = 0.009 microl/pmol P450/min). The present study showed that the two major metabolites of cilostazol in vitro, namely, OPC-13326 and OPC-13217, are mainly catalyzed by CYP3A4 and CYP3A5, respectively.

CYP2C19 polymorphism in Korean patients on warfarin therapy

This study was designed to assess the effect of CYP2C19 polymorphism on warfarin dosage requirements and bleeding complications in the Korean population. Patients were placed into one of four groups according to the dose of warfarin they received and the presence of bleeding complications: regular dose control, regular dose bleeding, low dose control, and low dose bleeding. Genotyping for CYP2C19*2 and CYP2C19*3 was performed by the restriction fragment length polymorphism method for each patient and each study group. The measured internal normalized ratio (INR) in each dose group was similar even though the administered dosage was significantly different. A total of 66 patients were evaluated for CYP2C19 polymorphism. Among them 25 patients (37.9%) were homozygous wild type. Four patients (6.1%) had heterozygous mutations at both loci. Others had mutations on either the CYP2C19*2 or *3 locus. Higher genetic variation was observed in CYP2C19*2 than in CYP2C19*3 among Korean patients on warfarin therapy. Our data suggested that there is a higher incidence of bleeding complications in patients who have a higher allele frequency of CYP2C19. It was also revealed that the distribution of CYP2C19 polymorphism among Asian populations is more similar than of the distribution among Caucasian populations.

Genotyping and haplotyping of CYP2C19 functional alleles on thin-film biosensor chips

OBJECTIVES

Numerous functional polymorphisms in the CYP2C19 gene have been identified; some alleles (e.g. CYP2C19*2 and CYP2C19*3) are associated with poor metabolism of CYP2C19 substrate drugs. Studies have found that the proportion of poor metabolizers, explained by CYP2C19*2 and CYP2C19*3, varies from less than 50% to more than 90% of poor metabolizers. Therefore, phenotype-genotype correlation studies should cover more than CYP2C19*2 and CYP2C19*3. A broader coverage, however, requires an easy-to-use and high-throughput genotyping platform. This broader coverage should also include the recently identified functional allele, CYP2C19*10, which involves a nucleotide change adjacent to the altered nucleotide change in CYP2C19*2. The currently used restriction fragment length polymorphism-based method for genotyping CYP2C19*2 cannot distinguish between CYP2C19*2 and CYP2C19*10. We aim to develop a simple platform that can genotype all CYP2C19 functional alleles.

METHODS

We have developed a thin-film biosensor chip platform to genotype 16 exonic CYP2C19 variants, including two sets of two adjacent single nucleotide polymorphisms and 12 single single nucleotide polymorphisms, using a ligation strategy.

RESULTS

We demonstrate that this is a rapid, accurate, and inexpensive method for genotyping CYP2C19 variants using individual's genomic DNA samples. We further demonstrate that this genotyping platform can be used to construct a haplotype structure of the CYP2C19 variants in a population, and to assign a haplotype combination to each individual on the basis of his/her genotype results.

CONCLUSION

This assay can be applied in pharmacogenomic studies in both basic research and clinical laboratories. It is also an ideal technology for pharmacogenomic tests in both developed and developing countries.

The future prospects of pharmacogenetics in oral anticoagulation therapy

Coumarins are the mainstay of oral anticoagulation for the treatment and prophylaxis of thromboembolic disorders. They have a narrow therapeutic index and regular monitoring is therefore required to avoid serious adverse effects. There is wide interindividual variability in dosage requirements, which makes anticoagulation response unpredictable. Current dosing titrations are haphazard and inconvenient and poor initial control leads to morbidity, and occasional mortality, because of bleeding and further thromboembolism. Recent discoveries have helped to characterize the factors that contribute to the interindividual variability in responses to coumarins. Patient and environmental factors that affect anticoagulation response to coumarins include age, body size, dietary vitamin K status, concurrent disease and drug interactions. More recently, single nucleotide polymorphisms in the 2C9 isoform of cytochrome P450 (CYP2C9) and vitamin K epoxide reductase (VKOR) have been shown to make significant contributions to the variability in coumarin dosage requirements. Polymorphisms in other genes that mediate the actions of coumarins may also contribute to this variability. Racial and cultural differences influence dosage requirements, which can be explained, at least in part, by genetic and dietary factors. Incorporation of genetic and environmental factors could help in the prediction of more individualized loading and maintenance doses for safer anticoagulation therapy.

A Semi-Physiological Population Pharmacokinetic Model Describing the Non-linear Disposition of Indisulam

The pharmacokinetic profile of the anti-cancer agent indisulam is non-linear. In addition to non-linear clearance, this may partially be explained by saturable distribution to red blood cells and saturable plasma protein binding. The aims of this study were to develop a semi-physiological population pharmacokinetic model of indisulam and to examine the impact of protein binding and distribution to red blood cells. Indisulam concentrations in plasma, plasma ultrafiltrate and in red blood cells from multiple phase I studies in Caucasian and Japanese patients were used to develop a pharmacokinetic model using NONMEM. This model comprised four physiological compartments: plasma, red blood cells, interstitial fluid and tissue. A simulation study was performed to examine the contribution of physiological processes in indisulam pharmacokinetics. Plasma albumin concentrations were predictive for the maximal protein binding capacity and considerably influenced total plasma concentrations of indisulam, whereas free plasma concentrations remained relatively unaffected. The maximal specific red blood cell binding capacity was 64.0 ( +/-5.9) mg/L and corresponded to the typical red blood cell carbonic anhydrase concentration. Simulation studies demonstrated that the hematocrit does not have a clinically relevant impact on indisulam disposition. This semi-physiological model allowed adequate prediction of the time profiles of indisulam concentrations in all monitored compartments for a large range of dose levels and several treatment regimens. The model has elucidated the mechanism and the role of saturable plasma protein binding and saturable distribution to red blood cells in indisulam pharmacokinetics and provides a basis for rationale PK-PD relationships.

Allele and genotype frequencies of CYP2C9 in a Korean population

AIMS

To determine the frequencies of the variant alleles and the genotypes of CYP2C9 in a Korean population.

METHODS

Three hundred and fifty-eight healthy Korean subjects were studied. CYP2C9 alleles were detected by polymerase chain reaction-restriction fragment length polymorphism assays and direct sequencing assays.

RESULTS

The allele frequencies were 0.934 for CYP2C9*1, 0.060 for CYP2C9*3 and 0.006 for CYP2C9*13. The CYP2C9*2,*4,*5 and *11 alleles were not detected. The frequencies of the CYP2C9*1/*1, *1/*3 and *1/*13 genotypes were 0.869, 0.120 and 0.011, respectively.

CONCLUSION

The frequency of the CYP2C9*3 allele in the Korean population studied was significantly higher than reported elsewhere, and a novel allele, CYP2C9*13, was found at a frequency of 0.006 (95% confidence interval 0, 0.012). Only three genotypes of CYP2C9, CYP2C9*1/*1,*1/*3 and *1/*13 were observed in this Korean population.

Effect of CYP2C19 genetic polymorphism on pharmacokinetics of phenytoin and phenobarbital in Japanese epileptic patients using Non-linear Mixed Effects Model approach

OBJECTIVE

To clarify the effect of genetic polymorphism of CYP2C19 on pharmacokinetics of phenytoin and phenobarbital using a Non-linear Mixed Effects Modelling analysis in Japanese epileptic patients.

METHOD

A total of 326 serum phenytoin concentrations were collected from 132 patients, and a total of 144 serum phenobarbital concentrations were collected from 74 patients during their clinical routine care.

RESULT

The maximal elimination rate of phenytoin decreased by 10.2% in patients with CYP2C19*1/*2 compared with patients with normal CYP2C19. The Michaelis-Menten constants in the patients with CYP2C19*1/*3 and the poor metabolizers of (CYP2C19*2/*2 or *2/*3 or *3/*3) were 27% and 54% higher than those for the patients with normal CYP2C19, respectively. The total body clearance of phenobarbital decreased by 19.3% in patients with CYP2C19*1/*3 or the poor metabolizers of CYP2C19 compared with patients with normal CYP2C19 or with CYP2C19*1/*2.

CONCLUSION

These findings indicated that the genetic polymorphisms of CYP2C19 contribute to the pharmacokinetic variability of phenytoin and phenobarbital, the poor metabolizers of CYP2C19, which are relatively common in Asian groups.

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.

Effect of CYP2C9 genetic polymorphisms on the efficacy and pharmacokinetics of glimepiride in subjects with type 2 diabetes

Glimepiride, a sulfonylurea hypoglycemic agent, is metabolized by cytochrome P450 2C9 (CYP2C9) which is known to have genetic polymorphisms. To examine the effects of CYP2C9 genetic polymorphisms on the safety and efficacy of glimepiride in patients with type 2 diabetes, the responses to the glimepiride were measured in Japanese type 2 diabetic patients with the different CYP2C9 genotype. The reduction in the HbA(1c) was significantly larger (P<0.05) among the CYP2C9*1/*3 subjects than among the CYP2C9*1/*1 subjects. The long-term observations of 2 patients with a CYP2C9*1/*3 suggested that subjects with a CYP2C9*1/*3 respond well to glimepiride during the initial phase of treatment, but 1 patient have shown the weight gain over the long-term treatment. The pharmacokinetic study showed that the area under the concentration-time curve for glimepiride in the CYP2C9*1/*3 subjects was approximately 2.5-fold higher than that of the CYP2C9*1/*1 subjects. The intrinsic clearance of glimepiride by the CYP2C9*3 enzyme was lower than that by the CYP2C9*1 enzyme. These results suggested that the lower hydroxylation activity of glimepiride in the subject with type 2 diabetes and CYP2C9*1/*3 led to a marked elevation in the plasma concentrations of glimepiride and a stronger pharmacological effect of glimepiride.

Papel del polimorfismo genético CYP2C19 en los efectos adversos a fármacos y en el riesgo para diversas enfermedades

There are a great number of polymorphic genes in the human genome. Many of them codify enzymes that metabolizes drugs and xenobiotic agents, including carcinogens. Among the better known of them, there are a number of isozymes of the microsomal oxidative system (CYP3A4, CYP2C9, CYP2C19 y CYP2D6). This article reviews the following issues: a) frequency of presentation of the "poor metabolizer" genotype and/or phenotype for substrates of CYP2C19; b) role of CYP2C19 polymorphism on the metabolism of some drugs (mephenytoine and other antiepileptic drugs, proton pump inhibitors, several antidepressants and anxyolitics, the antimalaria aggent proguanyl, and propranolol, among others, use this metabolic pathway), and c) possible role of CYP2C19 polymorphism in the risk for development of neoplasia and other diseases (systemic lupus erythematosus, psoriasis, hip osteonecrosis, Alzheimer's disease, amyotrophic lateral sclerosis, essential tremor).