Intermediate Metabolizer Group Research Articles

A study on CYP2C9 polymorphism in Puerto Rican Alzheimer's Patients and its role in the Pharmacokinetics of ∆-9-tetrahydrocanna-binol

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects over 55 million people worldwide. Individuals with AD are often prescribed multiple medications to manage comorbidities, many of which are metabolized by enzymes from the cytochrome P450 (CYP). CYP2C9 is expressed by the CYP2C9 gene. The highly polymorphic gene is grouped into phenotypes such as poor, intermediate, normal, and ultra-rapid metabolizers that influence the pharmacokinetics (PK) of drugs and their metabolites. Among humans, CYP2C9 is one of the most essential enzymes for metabolizing drugs, including delta-9-tetrahydrocannabinol (THC). The enzyme converts THC into its active metabolite 11-hydroxy-delta-9-THC (OH-THC). IGC-AD1 is a formulation with two active pharmaceutical ingredients, delta-9-THC and melatonin. The Phase 1, multiple ascending dose (MAD) trial, was conducted on a Puerto Rican population. The participant population in the trial (N=13) was 69.2% female and 30.8% male, with an average age of 80.18 (SD+/- 6.22). We report on the effect of CYP2C9 polymorphisms on the pharmacokinetics (PK) of THC and its active metabolite in AD patients from a Phase 1 trial. Using a Mass ARRAY Analyzer 4 Instrument (Invitae Inc.), we determined the following CYP2C9 alleles: *2, *3, *4, *5, *6, *8, *11, *13, *15, and found that 60% of participants (N=6) were carriers of at least one polymorphism including 1*/2* and 1*/3*. The participants with intermediate metabolizers (*1/*3 and *1/*2) showed an increased half-life of THC and OH-THC with major differences between the two intermediate metabolizer groups *1/*3 and *1/*2. In the trial more females were noted to be intermediate metabolizers than males. As polymorphisms of CYP2C9 affect the PK of THC and its metabolite, larger studies are needed to establish PK baselines for polymorphisms of CYP2C9. In the meantime, it is recommended that researchers exercise caution while dosing AD patients with THC.

Decreased Analgesic Effect of Tramadol in Japanese Patients with CYP2D6 Intermediate Metabolizers after Orthopedic Surgery.

Tramadol is metabolized by CYP2D6 to an active metabolite, which in turn acts as an analgesic. This study aimed to investigate the impact of CYP2D6 genotype on the analgesic effect of tramadol in clinical practice. A retrospective cohort study was performed in patients treated with tramadol for postoperative pain after arthroscopic surgery for rotator cuff injury during April 2017-March 2019. The impact of CYP2D6 genotypes on the analgesic effects was assessed by the numeric rating scale (NRS) pain scoring and analyzed by the Mann-Whitney U test. Stepwise multiple linear regression analysis was performed to identify predictive factors for the area under the time-NRS curve (NRS-AUC), which was calculated using the linear trapezoidal method. Among the 85 enrolled Japanese patients, the number of phenotypes with CYP2D6 normal metabolizer (NM) and intermediate metabolizer (IM) was n = 69 (81.1%) and n = 16 (18.9%), respectively. The NRS and NRS-AUC in the IM group were significantly higher than those in the NM group until Day 7 (p < 0.05). The multiple linear regression analysis indicated that the CYP2D6 polymorphism was a prediction factor of the high NRS-AUC levels in Days 0-7 (β = 9.52, 95% CI 1.30-17.7). In IM patients, the analgesic effect of tramadol was significantly reduced one week after orthopedic surgery in clinical practice. Therefore, dose escalation of tramadol or the use of alternative analgesic medications can be recommended for IM patients.

The influence of NUDT15 variants on 6-mercaptopurine-induced neutropenia in Vietnamese pediatric acute lymphoblastic leukemia.

6-Mercaptopurine (6-MP) serves as the backbone of maintenance therapy in acute lymphoblastic leukemia. The nucleoside diphosphate-linked moiety X-type motif 15 genes (NUDT15) affects the metabolism of 6-MP and thiopurine-related neutropenia in the Asian population. This study reports the influence of these variants on 6MP-induced neutropenia in children with acute lymphoblastic leukemia (ALL). A total of 102 children were enrolled in this retrospective cohort study. NUDT15 variants on exon 1 and exon 3 were identified by Sanger sequencing. We divided the intermediate metabolizer group and the normal metabolizer group base on NUDT15 diplotypes. During the first 3months of maintenance treatment, medical reports measured treatment-related toxicity (neutropenia) and 6-MP dose decreases. NUDT15 genotyping showed two categories of mutations: wild type (75.5%) and heterozygous variant (24.5%). Neutropenia during the early phase of maintenance therapy in the intermediate metabolizer group (68%) was significantly higher than the normal metabolizer group (18.2%) with 10-fold greater odds. Especially, the c.415C>T heterozygous variant was extremely associated with neutropenia compared with the C>C genotype (odds ratio [OR]: 12; 95% confidence interval [CI]: 3.5-41.7). The tolerated doses of 6-MP after the first 3months of maintenance therapy related to the intermediate metabolizer group and the normal metabolizer group were 48.7 and 64.3mg/m2/day, respectively (p<0.001). One-fourth of individuals had NUDT15 variations. All NUDT15 heterozygous mutations cause neutropenia and need 6-MP dose optimization. Given the frequency of NUDT15 mutations in Vietnamese children and their connection with early neutropenia, testing is indicated.

Clinical Impact of CYP2C19 Genotype on Clopidogrel-Based Antiplatelet Therapy After Percutaneous Coronary Intervention

BackgroundAlthough there is a growing body of evidence that CYP2C19 genotyping can be beneficial when considering treatment with clopidogrel after percutaneous coronary intervention (PCI), whether a genotype-guided strategy can be generally adopted in routine practice remains unclear among East Asians. ObjectivesThis study sought to investigate long-term outcomes of patients undergoing clopidogrel-based antiplatelet therapy after drug-eluting stent (DES) implantation according to CYP2C19 genotypes. MethodsFrom the nationwide multicenter PTRG-DES (Platelet function and genoType-Related long-term proGnosis in DES-treated patients) consortium, patients who underwent CYP2C19 genotyping were selected and classified according to CYP2C19 loss-of-function allele: rapid metabolizers (RMs) or normal metabolizers (NMs) vs intermediate metabolizers (IMs) or poor metabolizers (PMs). The primary outcome was a composite of cardiac death, myocardial infarction, and stent thrombosis at 5 years after the index procedure. ResultsOf 8,163 patients with CYP2C19 genotyping, 56.7% presented with acute coronary syndrome. There were 3,098 (37.9%) in the RM or NM group, 3,906 (47.9%) in the IM group, and 1,159 (14.2%) in the PM group. IMs or PMs were associated with an increased risk of 5-year primary outcome compared with RMs or NMs (HRadj: 1.42; 95% CI: 1.01-1.98; P = 0.041), and the effect was more pronounced in the first year (HRadj: 1.67; 95% CI: 1.10-2.55; P = 0.016). The prognostic implication of being an IM and PM was significant in acute coronary syndrome patients (HRadj: 1.88; 95% CI: 1.20-2.93; P = 0.005) but not in those with stable angina (HRadj: 0.92; 95% CI: 0.54-1.55; P = 0.751) (interaction P = 0.028). ConclusionsAmong East Asians with clopidogrel-based antiplatelet therapy after DES implantation, CYP2C19 genotyping could stratify patients who were likely to have an increased risk of atherothrombotic events. (Platelet Function and genoType-Related Long-term progGosis in DES-treated Patients: A Consortium From Multi-centered Registries [PTRG-DES]; NCT04734028)

Association of cytochromes P450 3A4*22 and 3A5*3 genotypes and polymorphism with response to simvastatin in hypercholesterolemia patients.

BackgroundsInter-individual variability in response to statin was mainly due to genetic differences. This study aimed to investigate the association of CYP3A4*22 (rs35599367), CYP3A5*3 (rs776746) single nucleotide polymorphism (SNP) with response to simvastatin in hypercholesterolemia patients conducted at King Abdulaziz University hospital (KAUH) in Jeddah, Saudi Arabia.Patients and methodsA total of 274 participants were registered in the current study. Hypercholesterolemic patients taking simvastatin 20 mg (n = 148) and control subjects (n = 126) were tested for rs35599367 and rs776746 genotypes using Custom Taqman ® Assay Probes. Response to simvastatin in these patients was assessed by determination of low density lipoprotein (LDL-C), total cholesterol (TC) and by measuring statin plasma levels using Liquid Chromatography-Mass Spectrometry (LC-MS).ResultsNone of the participants carried a homozygous CYP3A4*22 mutant genotype, while 12 (4.4%) individuals had a heterozygous genotype and 262 (95.6%) had a wild homozygous genotype. The CYP3A5*3 allele was detected in the homozygous mutant form in 16 (5.8%) individuals, while 74 (27.0%) individuals carried the heterozygous genotype and 184 (67.2%) carried the wildtype homozygous genotype. Of the patient group, 15 (11%) were classified as intermediate metabolizers (IMs) and 133 (89%) as extensive metabolizers (EMs). Plasma simvastatin concentrations for the combined CYP3A4/5 genotypes were significantly (P<0.05) higher in the IMs group than in the EMs group. TC and plasma LDL-C levels were also significantly (P<0.05) higher in IMs than in EMs.ConclusionThe present study showed associations between CYP3A4*22 (rs35599367) and CYP3A5*3 (rs776746) SNP combination genotypes with response to statins in hypercholesterolemia. Patients who had either a mutant homozygous allele for CYP3A5*3 or mutant homozygous and heterozygous alleles for CYP3A4*22 showed increased response to lower TC and LDL-C levels.

Combined Effect of CYP2C19 Genetic Polymorphisms and C-Reactive Protein on Voriconazole Exposure and Dosing in Immunocompromised Children.

BackgroundPediatric patients have significant interindividual variability in voriconazole exposure. The aim of the study was to identify factors associated with voriconazole concentrations and dose requirements to achieve therapeutic concentrations in pediatric patients.MethodsMedical records of pediatric patients were retrospectively reviewed. Covariates associated with voriconazole plasma concentrations and dose requirements were adjusted by using generalized linear mixed-effect models.ResultsA total of 682 voriconazole steady-state trough concentrations from 91 Chinese pediatric patients were included. Voriconazole exposure was lower in the CYP2C19 normal metabolizer (NM) group compared with the intermediate metabolizer (IM) group and the poor metabolizer (PM) group (p = 0.0016, p < 0.0001). The median daily dose of voriconazole required to achieve therapeutic range demonstrated a significant phenotypic dose effect: 20.8 mg/kg (range, 16.2–26.8 mg/kg) for the CYP2C19 NM group, 18.2 mg/kg (range, 13.3–21.8 mg/kg) for the CYP2C19 IM group, and 15.2 mg/kg (range, 10.7–19.1 mg/kg) for the CYP2C19 PM group, respectively. The extent of impact of C-reactive protein (CRP) levels on voriconazole trough concentrations and dose requirements varied between CYP2C19 phenotypes. Increases of 20, 120, 245, and 395 mg/L from 5 mg/L in CRP levels were associated with increases in voriconazole trough concentration by 22.22, 50, 64.81, and 75% respectively, in the NM group; by 39.26, 94.48, 123.93, and 146.63%, respectively, in the IM group; and by 17.17, 37.34, 46.78, and 53.65%, respectively, in the PM group. Meanwhile, increases of 20, 120, 245, and 395 mg/L from 5 mg/L in CRP levels were associated with increases in voriconazole dose requirements by 7.15, 14.23, 17.35, and 19.43%, respectively, in the PM group; with decreases in voriconazole dose requirements by 3.71, 7.38, 8.97, and 10.03%, respectively, in the NM group; and with decreases by 4, 9.10, 11.05, and 12.35%, respectively, in the IM group. In addition, age and presence of immunosuppressants had significant effects on voriconazole exposure.ConclusionsOur study suggests that CYP2C19 phenotypes, CRP concentrations, age, and the presence of immunosuppressants were factors associated with the pharmacokinetic changes in voriconazole. There was heterogeneity in the effect of CRP on voriconazole plasma concentrations across different CYP2C19 genotypes. Combining relevant factors with dose adaptation strategies in therapeutic drug monitoring may help to reduce the incidence of subtherapeutic and supratherapeutic concentrations in clinical practice.

Influence of CYP2C19 Polymorphisms on the Pharmacokinetics of Omeprazole in Elderly Subjects.

Omeprazole blocks the gastric H+ /K+ adenosine triphosphatase, thus inhibiting gastric acid secretion, and is metabolized by cytochrome P450 (CYP) 2C19. Due to the physiological changes in the elderly, there are different pharmacokinetic consequences compared to young people. The aim of this study was to evaluate the pharmacokinetic profiles of omeprazole in 15 elderly participants according to the CYP2C19 genotype. The concentration-time profiles of omeprazole and its metabolites, 5-hydroxy (5-OH) omeprazole and omeprazole sulfone, were similar between the CYP2C19 extensive metabolizer (EM) and intermediate metabolizer groups. In contrast, when comparing the EM group and CYP2C19 poor metabolizer (PM) group, the EM/PM geometric mean ratio (95% confidence interval) of area under the plasma concentration-time curve from time of dosing to the last measurable concentration was 0.52 (0.27-1.01) and that of the IM group was 0.71 (0.32-1.59), indicating that the exposure of omeprazole in the PM group was increased. The exposure of 5-OH omeprazole was significantly decreased in the PM group when compared to the EM group, with an EM/PM geometric mean ratio (95% confidence interval) of 2.20 (1.50-3.22). In conclusion, the tendency of drug exposure according to the CYP2C19 genotype in the elderly and young adults was similar in that the exposure level was highest in the PM group. However, when compared to young adults, the difference between the genotype groups was smaller in the elderly.

Influence of cytochrome P450 2D6 polymorphism on hippocampal white matter and treatment response in schizophrenia

Cytochrome P450 2D6 (CYP2D6) is expressed at high levels in the brain and plays a considerable role in the biotransformation and neurotransmission of dopamine. This raises the question of whether CYP2D6 variations and its impact on the brain can confer susceptibility to schizophrenia. We investigated the possible links among the CYP2D6 genotype, white matter (WM) integrity of the hippocampus, and the treatment response to antipsychotic drugs in Korean patients with schizophrenia (n = 106). Brain magnetic resonance imaging and genotyping for CYP2D6 were conducted at baseline. The severity of clinical symptoms and the treatment response were assessed using the Positive and Negative Syndrome Scale (PANSS). After genotyping, 43 participants were classified as intermediate metabolizers (IM), and the remainder (n = 63) were classified as extensive metabolizers (EM). IM participants showed significantly higher fractional anisotropy (FA) values in the right hippocampus compared to EM participants. Radial diffusivity (RD) values were significantly lower in the overlapping region of the right hippocampus in the IM group than in the EM group. After 4 weeks of antipsychotic treatment, the EM group showed more improvements in positive symptoms than the IM group. FAs and RDs in the CYP2D6-associated hippocampal WM region were significantly correlated with a reduction in the positive symptom subscale of the PANSS. Greater improvements in positive symptoms were negatively associated with FAs, and positively associated with RDs in the right hippocampal region. The findings suggest that CYP26D-associated hippocampal WM alterations could be a possible endophenotype for schizophrenia that accounts for individual differences in clinical features and treatment responses.

CYP2D6 Genotype-Based Dose Recommendations for Risperidone in Asian People.

The aim of this study was to provide dose recommendations for risperidone in Asian people based on cytochrome P450 enzyme CYP2D6 genotype. First, we investigated the influence of CYP2D6 polymorphism on the pharmacokinetics of risperidone in Chinese patients with schizophrenia. Then, we performed a search for studies covering the relationship between pharmacokinetic parameters of risperidone and CYP2D6 genotype. Pooled pharmacokinetic parameters were meta-analyzed using a random-effects model. Lastly, we calculated the dose adjustment for risperidone based on CYP2D6 genotype for white and Asian people. Significant differences between the extensive metabolizer and intermediate metabolizer groups were observed for dose-adjusted risperidone level, 9-hydroxyrisperidone level, and risperidone/9-hydroxyrisperidone ratio, but not for the total active moiety. Meta-analysis showed that significant differences were observed among the four phenotype groups, including steady state concentration, peak risperidone concentration, and the area under the curve, using the Kruskal-Wallis test. No differences were found in oral clearance. For risperidone, dose recommendations for poor and ultrarapid metabolizers of CYP2D6 for Asians were different compared to that for white people for poor metabolizers (dose adjustment around 45% for white people, while for Asians the risperidone dose should be reduced by 26%). For ultrarapid metabolizers, risperidone dose should be increased by about 33% for white people and 30% for Asians. This was a first attempt to apply pharmacogenetics to suggest dose-regimens for Asian people; further research to replicate and extend these findings is recommended.

Effect of CYP2C19 Gene Polymorphisms on Proton Pump Inhibitor, Amoxicillin, and Levofloxacin Triple Therapy for Eradication of Helicobacter Pylori.

BackgroundThe effects of PPI are variable owing to the CYP2C19 polymorphisms. However, whether the polymorphisms could affect the Hp eradication efficacy of triple therapy is still not clear. The present study aimed to assess the effects of CYP2C19 gene polymorphisms on proton pump inhibitor (PPI), amoxicillin, and levofloxacin triple therapy for Helicobacter pylori (Hp) eradication.Material/MethodsWe randomly assigned 160 Hp-positive patients with chronic gastritis to 2 groups to receive either 20 mg bid omeprazole (OAL group, n=80) or 10 mg bid rabeprazole (RAL group, n=80), combined with 1000 mg bid amoxicillin and 500 mg qd levofloxacin. The 2 groups were treated for 10 days. The CYP2C19 genotypes included wild-type, M1 mutant gene (*2, the mutation of exon 5), and M2 mutant gene (*3, the mutation of exon 4) identified by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFIP). According to CYP2C19 genotype combinations, the patients were divided into extensive metabolizer (EM), intermediate metabolizer (IM), and poor metabolizer (PM) subgroups. The eradication efficacy of Hp was evaluated by 14C-UBT at 28 days after treatment.ResultsThe trial was completed by 155 patients. Hp eradication rates in OAL and RAL groups were 78.2% and 88.3%, respectively, on per-protocol (PP) analysis, indicating no significant difference (P>0.05). Regarding CYP2C19 genotypes, eradication rates of 60.7%, 84.2%, and 100% were obtained for EM, IM, and PM subgroups, respectively, of the OAL group. EM group eradication rates were significantly lower than IM and PM group values (P<0.05). In the RAL group, no such difference was observed (P>0.05). Hp eradication rates were significantly lower in the EM subgroup of the OAL group compared with that of the RAL group.ConclusionsHp eradication rates were higher in the RAL group than in OAL-treated patients. Interestingly, omeprazole-based therapy was significantly affected by the CYP2C19 genotype, unlike the rabeprazole-based therapy.

Application of Genetic Testing for CYP 450 Polymorphism to Predict Response to Clopidogrel Inpatient Undergoing PCI

AbstractIntroduction: The anti-platelet agent clopidogrel is a commonly prescribed medication in patients in patients who are undergoing percutaneous coronary intervention. Response to clopidogrel varies substantially due to genetic and acquired factors. Patients who experience recurrent cardiovascular ischemic or thrombotic events while taking clopidogrel are typically described as non-responsive or resistant. In our study was planned to assess the utility of pharmaco-genetic testing (CYP2C19) for clopidogrel response and application of the data for modification of anti-platelet regimen accordingly. Methods: This is a prospective nonrandomized ethical committee approved study from our institute. We included the post PCI patients presented with chronic stable angina and acute coronary syndrome (who has less bleeding risk score) with good left ventricular function. Along with the demographic and clinical features, we collected the data of platelet aggregation test (light transmission of aggregometry), CYP2C19 genetic analysis test and clinical outcome at the time of discharge, at 15days of discharge and end of 3 months. CYP2C19 genetic analysis is done by method of DNA based clopidogrel resistance genotyping test. We grouped the cases as extensive metabolizers (EM) and intermediate metabolizers (IM) depending on CYP2C19genetic analysis into two groups.Results: A total of 33 patients are included in this study. Among 33 cases, 25(75.7%) cases are male patients and 8(24.2%) cases are female patient, 18 (54.5%) patients are diabetic Mellitus, 20(60.6%) patient are hypertensives, 7(21.2%) cases are smokers and 5 (15.1%) case are alcoholic. We have diagnosed 20(60.6%) cases of unstable angina and 13(39.4%) cases of chronic stable angina. The average Meheran bleeding risk score is 9.8. Age, risk factors are comparable between the the EM and IM group. But presentation of ACS is more in IM (p=0.001).Follow up at 3 months, one died suddenly (probable stent thrombosis) in EM group. No other MACE occurred in both the groups. Multivariate analysis with binary logistic regression showed that only presentation as ACS is statistically significant in IM (p=0.001). Platelet aggregation showed tendency towards statistical significance (p=0.08) in EM patient. With all other parameters including MACE (p=0.3), there is no statistical significance by multivariate analysis.Conclusion: In our small prospective clinical and genetic analysis of clopidogrel metabolizer status has shown that intermediate metabolizer status of the patient is statistically more in unstable angina (p=0.003). There is tendency for statistically significance between the platelet aggregation test (p=0.08) and extensive metabolizer status of the patient. Whatever may be the status of the clopidogrel metabolizing condition, there is no difference in MACE.

Putting CYP2C19 genotyping to the test: utility of pharmacogenomic evaluation in a voriconazole-treated haematology cohort.

The clinical utility of pharmacogenomic testing in haematology patients with invasive fungal disease (IFD) receiving azole therapy has not been defined. We report our experience with CYP2C19 testing in haematological patients requiring voriconazole therapy for IFD. As a single-centre pilot study, 19 consecutive patients with a haematological malignancy undergoing active chemotherapy with a possible, probable or proven IFD requiring voriconazole therapy underwent CYP2C19 testing from 2013 to 2014. Baseline patient demographics, concurrent medications, voriconazole levels and IFD history were captured. The median voriconazole levels for intermediate metabolizer (IM) (CYP2C19*2 or 3/*1 or 17), extensive metabolizer (EM) (CYP2C19*1/*1) and heterozygote ultrarapid metabolizer (HUM)/ultrarapid metabolizer (UM) (UM, CYP2C19*17/*17; HUM, CYP2C19*1/*17) patients were 5.23, 3.3 and 1.25 mg/L, respectively. Time to therapeutic voriconazole levels was longest in the IM group, whilst voriconazole levels <1 mg/L were only seen in UM, HUM and EM phenotypes. The highest rates of clinical toxicity were seen in the IM group (3/5, 60%). Voriconazole exposure and toxicity was highest for IM and lowest for HUM/UM phenotypes. Time to therapeutic voriconazole level was longest in IM, whilst refractory subtherapeutic levels requiring CYP2C19 inhibition were only seen in the EM, HUM and UM phenotypes. CYP2C19 genotyping may predict those likely to have supratherapeutic or subtherapeutic levels and/or toxicity. Prospective evaluation of clinical pathways incorporating genotyping and voriconazole dose-titrating algorithms is required.

Hypertension and kidney disease

The response to clopidogrel, and some kind of the drug interaction are multifactorial.We enrolled 174 consecutive patients and determined CYP2C19 genotypes, measured platelet aggregation, and assessed the relationship between CYP2C19 genotype and platelet reactivity 24 hours after clopidogrel administration, and the risk of cardiovascular events over 18 months follow-up. A sub analysis examined the impact of rabeprazole, a proton pump inhibitor (PPI) less affected by CYP2C19.The CYP2C19 genotype was extensive metabolizer (EM) in 36%, intermediate metabolizer (IM) in 45%, and poor metabolizer (PM) in 19%. Platelet reactivity was significantly lower in the EM group than in the IM and PM groups (EM, IM, PM: 3560 ± 1404, 4203 ± 1302, 5084 ± 1007 AU•min, P < 0.05). The cardiovascular event rate was higher in the IM and PM groups than in the EM group (12.7% and 12.5% vs 1.6%; Hazard ratio for IM 10.6, P = 0.029; for PM 11.3, P = 0.040). No differences were seen between patients taking (N = 50) and not taking (N = 124) rabeprazole in residual platelet aggregation (4407 ± 1360 vs 4048 ± 1394, AU•min, P = 0.2782), or in cardiovascular events (10.0% vs 8.1%, HR 0.97, P = 0.97).CYP2C19 genotype is associated with an increased risk of cardiovascular events following stent implantation in Japanese patients.

Pharmacogenetics of uridine diphosphate glucuronosyltransferase (UGT2B7) genetic polymorphism on valproic acid pharmacokinetics in epilepsy

Background Sodium valproate is a widely prescribed broad-spectrum antiepileptic drug. It shows high inter-individual variability in pharmacokinetics and pharmacodynamics and has a narrow therapeutic range [1]. We evaluated the effects of polymorphic Uridine diphosphate glucuronosyltransferase (UGT2B7) metabolizing enzyme on the pharmacokinetics of sodium valproate in the patients with epilepsy who showed toxicity to therapy. Materials and methods Genotype analysis of the patients was made with polymerase chain–restriction fragment length polymorphism (RFLP) with sequencing. Plasma drug concentrations were measured with reversed phase high-performance liquid chromatography (HPLC) and concentration–time data were analyzed by using a non-compartmental approach. Results The results of this study suggested a significant genotypic as well as allelic association with valproic acid toxicity for UGT2B7 polymorphic enzymes. The elimination half-life (t1/2=42.2 h) of valproic acid was longer and the clearance rate (CL=947 ml/h) was lower in the poor metabolizers group of UGT2B7 polymorphism who showed toxicity than in the intermediate metabolizers group (t1/2 = 36.5 h, CL = 1,042 ml/h) or the extensive metabolizers group (t1/2 = 27. h, CL = 1,602 ml/h).Conclusions Our findings suggest that the UGT2B7 genetic polymorphism plays a significant role in the steady state concentration of valproic acid, and it thereby has an impact on the toxicity of the valproic acid used in the patients with epilepsy.

Effects of CYP2C19 Genetic Polymorphisms on Atomoxetine Pharmacokinetics

Atomoxetine is a selective norepinephrine reuptake inhibitor indicated for the treatment of attention-deficit/hyperactivity disorder. Atomoxetine metabolism is mediated by CYP2D6 and CYP2C19. This study aimed to investigate the effect of the CYP2C19 genetic polymorphism on the pharmacokinetics of atomoxetine and its metabolites, 4-hydroxyatomoxetine and N-desmethylatomoxetine. A single 40-mg oral dose of atomoxetine was administered to 40 subjects with different CYP2C19 genotypes (all participants carried the CYP2D6*1/*10 genotype). Concentrations of atomoxetine and its metabolites were analyzed using high-performance liquid chromatography with tandem mass spectrometry in plasma samples that were collected up to 24 hours after drug intake. For atomoxetine, the CYP2C19 poor metabolizer (PM) group showed significantly increased maximum plasma concentration and AUC0-∞ (area under the plasma concentration-time curve from 0 to infinity) and decreased apparent oral clearance compared with samples of the CYP2C19 extensive metabolizer (EM) and intermediate metabolizer (IM) groups (P < 0.001 for all). The half-life of atomoxetine in the CYP2C19PM group was also significantly longer than in the other genotype groups (P < 0.01 for CYP2C19EM and P < 0.05 for CYP2C19IM groups). The maximum plasma concentration and AUC 0-∞ of 4-hydroxyatomoxetine were significantly higher in the CYP2C19PM group compared with those in the CYP2C19EM and IM groups (P < 0.001 for CYP2C19EM and P < 0.05 for CYP2C19IM, respectively), whereas the corresponding values for N-desmethylatomoxetine in the CYP2C19PM group were significantly lower than those in the 2 genotype groups (P < 0.001 for both genotype groups). These results suggest that the genetic polymorphisms of CYP2C19 significantly affect the pharmacokinetics of atomoxetine.

Impact of CYP2C19 Polymorphism and Proton Pump Inhibitors on Platelet Reactivity to Clopidogrel and Clinical Outcomes Following Stent Implantation

The response to clopidogrel, and some kind of the drug interaction are multifactorial. We enrolled 174 consecutive patients and determined CYP2C19 genotypes, measured platelet aggregation, and assessed the relationship between CYP2C19 genotype and platelet reactivity 24hours after clopidogrel administration, and the risk of cardiovascular events over 18months follow-up. A sub analysis examined the impact of rabeprazole, a proton pump inhibitor (PPI) less affected by CYP2C19. The CYP2C19 genotype was extensive metabolizer (EM) in 36%, intermediate metabolizer (IM) in 45%, and poor metabolizer (PM) in 19%. Platelet reactivity was significantly lower in the EM group than in the IM and PM groups (EM, IM, PM: 3560±1404, 4203±1302, 5084±1007AU•min, P<0.05). The cardiovascular event rate was higher in the IM and PM groups than in the EM group (12.7% and 12.5% vs 1.6%; Hazard ratio for IM 10.6, P=0.029; for PM 11.3, P=0.040). No differences were seen between patients taking (N=50) and not taking (N=124) rabeprazole in residual platelet aggregation (4407±1360 vs 4048±1394, AU•min, P=0.2782), or in cardiovascular events (10.0% vs 8.1%, HR 0.97, P=0.97). CYP2C19 genotype is associated with an increased risk of cardiovascular events following stent implantation in Japanese patients.

Correlation of CYP2C19 Phenotype With Voriconazole Plasma Concentration in Children

Voriconazole is a triazole antifungal agent with potent activity against a broad spectrum of pathogens, including Aspergillus and Candida species. In human adults, allelic polymorphisms of CYP2C19 are known to correlate with significant variation in voriconazole plasma concentration. Here, we report an analysis of CYP2C19 phenotype and voriconazole plasma concentrations in children. This retrospective study included 37 children who had voriconazole plasma concentrations measured from May 2006 to June 2011. All had single-nucleotide polymorphisms that define the 3 major CYP2C19 alleles. Patients were classified as follows: normal metabolizers, intermediate metabolizers, poor metabolizers, or hypermetabolizers. The frequencies of the 3 CYP2C19 genetic polymorphisms were similar to those previously reported for Japanese adults. Trough plasma concentrations of voriconazole were significantly higher in the poor metabolizer and intermediate metabolizer groups compared with the normal metabolizer and hypermetabolizer groups (P=0.004). Two patients with high plasma concentrations experienced voriconazole-related severe adverse events (syndrome of inappropriate antidiuretic hormone secretion and cardiac toxicities). The current study suggests that a significant association exists in children between the voriconazole plasma concentration and the CYP2C19 phenotype. Dose adjustment based on CYP2C19 phenotype may be useful during voriconazole therapy, especially for Japanese children, who as a group have a higher incidence of the poor metabolizer and intermediate metabolizer phenotypes.

The Effect of Uridine Diphosphate Glucuronosyltransferase (UGT)1A6 Genetic Polymorphism on Valproic Acid Pharmacokinetics in Indian Patients with Epilepsy: A Pharmacogenetic Approach

Sodium valproate is a widely prescribed broad-spectrum antiepileptic drug. It shows high inter-individual variability in pharmacokinetics and pharmacodynamics and has a narrow therapeutic range. We evaluated the effects of polymorphic uridine diphosphate glucuronosyltransferase (UGT)1A6 (541A>G, 552A>C) metabolizing enzyme on the pharmacokinetics of sodium valproate in the patients with epilepsy who showed toxicity to therapy. Genotype analysis of the patients was made with polymerase chain-restriction fragment length polymorphism (RFLP) with sequencing. Plasma drug concentrations were measured with reversed phase high-performance liquid chromatography (HPLC) and concentration-time data were analyzed by using a non-compartmental approach. The results of this study suggested a significant genotypic as well as allelic association with valproic acid toxicity for UGT1A6 (541A>G) or UGT1A6 (552A>C) polymorphic enzymes. The elimination half-life (t ½=40.2h) of valproic acid was longer and the clearance rate (CL=917ml/h) was lower in the poor metabolizers group of UGT1A6 (552A>C) polymorphism who showed toxicity than in the intermediate metabolizers group (t ½=35.5h, CL=1,022ml/h) or the extensive metabolizers group (t ½=25.4h, CL=1,404ml/h). Our findings suggest that the UGT1A6 (552A>C) genetic polymorphism plays a significant role in the steady state concentration of valproic acid, and it thereby has an impact on the toxicity of the valproic acid used in the patients with epilepsy.

Analysis of CYP2D6 genotype and response to tetrabenazine

Tetrabenazine is effective in the treatment of the chorea associated with Huntington disease and other hyperkinetic movement disorders. Following oral administration, tetrabenazine is hepatically transformed into 2 active metabolites that are CYP2D6 substrates. There are 4 CYP2D6 genotypes: poor metabolizers, intermediate metabolizers, extensive metabolizers, and ultrarapid metabolizers. CYP2D6 genotyping was performed on sequential subjects treated with tetrabenazine, but results were not known at the time of titration. Duration of titration to a stable dose, total daily dose, response rating scores, and adverse events were retrospectively collected and subsequently analyzed. Of 127 patients, the majority (n = 100) were categorized as extensive metabolizers, 14 as intermediate metabolizers, 11 as poor metabolizers, and 2 as ultrarapid metabolizers. Ultrarapid metabolizer patients needed a longer titration (8 vs 3.3, 4.4, and 3 weeks, respectively; P < .01) to achieve optimal benefit and required a higher average daily dose than the other patients, but this difference did not reach statistical significance. The treatment response was less robust in the intermediate metabolizer group when compared with the extensive metabolizer patients (P = .013), but there were no statistically significant differences between the various groups with regard to adverse effects. Our findings demonstrate that, aside from the need for a longer titration in the ultrarapid metabolizers, there are no distinguishing features of patients with various CYP2D6 genotypes, and therefore the current recommendation to systematically genotype all patients prescribed more than 50 mg/day of tetrabenazine should be reconsidered.

Impact of CYP2D6 Polymorphisms on Tamoxifen Responses of Women with Breast Cancer: A Microarray-based Study in Thailand

This study was designed to investigate the frequency of CYP2D6 polymorphisms and evaluate the association between genetic polymorphisms of CYP2D6 and tamoxifen therapeutic outcome in Thai breast cancer patients. We recruited 48 breast cancer patients who received adjuvant tamoxifen for evaluating CYP2D6 genetic polymorphisms using microarray-based technology. Associations between genotypes-phenotypes and disease free survival were analyzed. Median follow up time was 5.6 years. The mean age of the subjects was 50 years. The 3 common allelic frequencies were 43.8% (*10), 36.5 (*1) and 10.4% (*2) which are related to extensive metabolizer (EM) and intermediate metabolizer (IM) with 70.8% and 29.2 %, respectively. No association between CYP2D6 genotypes and DFS was demonstrated. Nevertheless, exploratory analysis showed statistically significant shorter DFS in the IM group of post-menopause patients (HR, 6.85; 95% CI, 1.48 -31.69; P = 0.005). Furthermore, we observed statistically significant shorter DFS of homozygous CYP2D6*10 when compared with heterozygous CYP2D6*10 and other genotypes (P=0.005). CYP2D6*10 was the most common genotype in our subjects. Post-menopause patients with homozygous CYP2D6*10 and IM have shorter DFS. To confirm this relationship, larger samples and comprehensively designed trials in Thailand are required.