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

Association of variants in the ABCB1, CYP2C19 and CYP2C9 genes for Juvenile Myoclonic Epilepsy

Juvenile myoclonic epilepsy (JME) is the most common of the generalized genetic epilepsies, with multiple causal and susceptibility genes; however, its etiopathogenesis is mainly unknown. The toxic effects caused by xenobiotics in cells occur during their metabolic transformation, mainly by enzymes belonging to cytochrome P450. The elimination of these compounds by transporters of the ABC type protects the central nervous system, but their accumulation causes neuronal damage, resulting in neurological diseases. The present study has sought the association between single nucleotide genetic variants of the CYP2C9, CYP2C19, and ABCB1 genes and the development of JME in patients compared to healthy controls. The CC1236 and GG2677 genotypes of ABCB1 in women; allele G 2677, genotypes GG 2677 and CC 3435 in men; the CYP2C19*2A allele, and the CYP2C19*3G/A genotype in both sexes were found to be risk factors for JME. Furthermore, carriers of the TTGGCC genotype combination of the ABCB1 gene (1236/2677/3435) have a 10.5 times higher risk of developing JME than non-carriers. Using the STRING database, we found an interaction between the proteins encoded by these genes and other possible proteins. These findings indicate that the CYP450 system and ABC transporters could interact with other genes in the JME.

Therapeutic Drug Monitoring of Voriconazole in Patients with End-Stage Liver Disease

BACKGROUND

This study aimed to identify the factors that influence voriconazole (VCZ) plasma concentrations and optimize the doses of VCZ in patients with end-stage liver disease (ESLD).

METHODS

Patients with ESLD who received a VCZ maintenance dose of 100 mg twice daily (group A, n = 57) or the VCZ maintenance dose of 50 mg twice daily (group B, n = 37), orally or intravenously, were enrolled in this study. Trough plasma concentrations (Cmin) of VCZ between 1 and 5 mg/L were considered within the therapeutic target range.

RESULTS

The VCZ Cmin was determined in 94 patients with ESLD. The VCZ Cmin of patients in group A was remarkably higher than those in group B (4.85 ± 2.53 mg/L vs 2.75 ± 1.40 mg/L; P < 0.001). Compared with group A, fewer patients in group B had VCZ Cmin outside the therapeutic target (23/57 vs. 6/37, P = 0.021). Univariate and multivariate analyses suggested that both body weight and Model for End-Stage Liver Disease scores were closely associated with the VCZ Cmin in group B.

CONCLUSIONS

These data indicate that dose optimization based on body weight and Model for End-Stage Liver Disease scores is required to strike an efficacy-safety balance during VCZ treatment in patients with ESLD.

Population pharmacokinetic and exposure-response analysis of apremilast in Japanese subjects with moderate to severe psoriasis

Apremilast is an orally available phosphodiesterase 4 inhibitor used for the treatment of moderate to severe psoriasis. The aims of this analysis were to develop a population pharmacokinetic (PPK) model of apremilast based on observed data from phase 1 studies combined with clinical trial data from subjects with moderate to severe psoriasis, and to develop exposure–response (E‐R) models to determine whether Japanese subjects with moderate to severe psoriasis achieve response to apremilast treatment similar to that observed in non‐Japanese, predominantly Caucasian subjects with moderate to severe psoriasis. The PPK model demonstrated that apremilast plasma concentrations and overall apparent clearance rate were comparable between the Japanese and Caucasian subgroups. The E‐R analyses of ≥75% or ≥50% improvement from baseline in Psoriasis Area and Severity Index score and achievement of static Physician Global Assessment score of 0 (clear) or 1 (almost clear) at week 16 indicated that apremilast treatment in Japanese subjects approached the maximal effect with response rates comparable to those in predominantly Caucasian subjects. Overall, the analyses confirm that the approved apremilast 30 mg b.i.d. dose is appropriate for Japanese subjects with moderate to severe psoriasis, with an efficacy profile similar to that previously observed in Caucasian subjects.

Physiologically based pharmacokinetic (PBPK) modeling for prediction of celecoxib pharmacokinetics according to CYP2C9 genetic polymorphism

Celecoxib is a non-steroidal anti-inflammatory drug (NSAID) and a representative selective cyclooxygenase (COX)-2 inhibitor, which is commonly prescribed for osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, acute pain, and primary dysmenorrhea. It is mainly metabolized by CYP2C9 and partly by CYP3A4 after oral administration. Many studies reported that CYP2C9 genetic polymorphism has significant effects on the pharmacokinetics of celecoxib and the occurrence of adverse drug reactions. The aim of this study was to develop a physiologically based pharmacokinetic (PBPK) model of celecoxib according to CYP2C9 genetic polymorphism for personalized pharmacotherapy. Initially, a clinical pharmacokinetic study was conducted where a single dose (200 mg) of celecoxib was administered to 39 healthy Korean subjects with CYP2C9*1/*1 or CYP2C9*1/*3 genotypes to obtain data for PBPK development. Based on the conducted pharmacokinetic study and a previous pharmacokinetic study involving subjects with CYP2C9*1/*13 and CYP2C9*3/*3 genotype, PBPK model for celecoxib was developed. A PBPK model for CYP2C9*1/*1 genotype group was developed and then scaled to other genotype groups (CYP2C9*1/*3, CYP2C9*1/*13 and CYP2C9*3/*3). After model development, model validation was performed with comparison of five pharmacokinetic studies. As a result, the developed PBPK model of celecoxib successfully described the pharmacokinetics of each CYP2C9 genotype group and its predicted values were within the acceptance criterion. Additionally, all the predicted values were within two-fold error range in comparison to the previous pharmacokinetic studies. This study demonstrates the possibility of determining the appropriate dosage of celecoxib for each individual through the PBPK modeling with CYP2C9 genomic information. This approach could contribute to the reduction of adverse drug reactions of celecoxib and enable precision medicine.

Metabolizer phenotype prediction in different Peruvian ethnic groups through CYP2C9 polymorphisms

OBJECTIVES

The CYP2C9 gene have three common alleles, CYP2C9*1, CYP2C9*2 and CYP2C9*3, associated with different homozygous (*1/*1, *2/*2 and *3/*3) and heterozygous (*1/*2 and *1/*3) genotypes, which in turn are related to extensive (gEM), intermediate (gIM) and poor (gPM) metabolizers. Likewise, the inter-ethnic variability was intimately associated with different drug metabolism. Therefore, the aim of the present study was predict the metabolizer phenotypes in different Peruvian ethnic groups from lowland (<2,500 m) and highland (>2,500 m).

METHODS

TaqMan genotyping assays were performed in a group of 174 healthy unrelated Peruvian individuals.

RESULTS

In this study, the allelic comparison between the three eco-regions showed that the CYP2C9*1 was the most common in Andean (96.32%); the *2 was the most frequent in Coast (7.45%, p<0.05). Regarding the *3 was the most common in Amazonian (6.25%, p<0.05). In a corroborative manner, the gEM was the most common in Andean (94.74%), the gIM in Coast (17.02%) and gPM in Amazonian (6.25%) populations.

CONCLUSIONS

Our study provides a valuable source of information about to metabolizer phenotype drugs in different Peruvian ethnic groups. In this way, it could be established suitable genetic-dosage medicaments for various common diseases in these heterogenetic populations.

Drug interaction between letermovir and voriconazole after allogeneic hematopoietic cell transplantation

Letermovir has been approved for the prevention of cytomegalovirus (CMV) infection after allogeneic hematopoietic stem cell transplantation (HCT). Letermovir is a cytochrome P450 (CYP) 2C19 inducer. Voriconazole, which is a broad-spectrum triazole antifungal agent, is mainly metabolized by CYP2C19. Thus, voriconazole trough concentration may decrease due to the drug interaction between voriconazole and letermovir. This study aimed to clarify the effects of letermovir on voriconazole trough concentration in allogeneic HCT recipients. We retrospectively examined voriconazole trough concentration in 24 allogeneic HCT recipients who had letermovir for prevention of CMV infection. The median voriconazole C/D ratios significantly decreased after starting letermovir from 0.25 L/kg to 0.11 L/kg (p < 0.01), and increased after discontinuing letermovir from 0.15 L/kg to 0.24 L/kg (p = 0.02). The median fold change of voriconazole trough concentration during letermovir administration was 0.40. Our results suggest that voriconazole trough concentration decreases when voriconazole is combined with letermovir in allogeneic HCT recipients. Therefore, close therapeutic drug monitoring of voriconazole trough concentration is warranted in allogeneic HCT recipients after starting or discontinuing letermovir.

CYP2C9 Variations and Their Pharmacogenetic Implications Among Diverse South Asian Populations

Introduction

Allelic frequency distribution of drug metabolizing enzyme genes among populations is important to identify risk groups for adverse drug reaction and to select representative populations for clinical trials. Although India emerged as an important hub for clinical trials, information about the pharmacogenetic diversity for this region is still lacking. Here, we investigated genetic diversity of cytochrome-P450-2C9 (CYP2C9) gene which metabolizes wide range of drugs and is highly expressed in the human liver.

Methods

In total, 1278 individuals from 36 diverse Indian populations, 210 individuals from in-house data-repository and 489 other South Asian samples from the 1000 Genomes Project were selected. Variants observed in CYP2C9 gene were subjected to various statistical analyses.

Results

High frequency of CYP2C9*3 (~13%) and CYP2C9*3/*3 (~1%) was observed among South Asians, compared to 21 populations living outside the Indian subcontinent. The allelic/genotypic frequency does not correlate with geographical location or linguistic affiliation, except populations speaking Tibeto-Burmans language, who have lower frequency of CYP2C9*3 and CYP2C9*3/*3. Since, South Asians practice strict endogamy, presence of unique mutation and high frequency of homozygous genotypes not surprising. CYP2C9*3 has been associated with therapeutic response.The effect of CYP2C9*3/*3 is more pronounced compared to heterozygous and wild type homozygous genotypes as evident in many in vitro studies. As South Asians have high frequency, it would be interesting to explore potential of CYP2C9*3 as a marker for personalized therapy. Our study revealed several rare functional variants, which form eight novel and rare haplotypes of CYP2C9 (CYP2C9*63–*70). Of which, CYP2C9*64, *65, *66, *68, *69 and *70 haplotypes are South Asian-specific.

Conclusion

Overall, we find high genetic heterogeneity within South Asians and identified South Asian-specific putative functional CYP2C9 haplotypes. High frequency of CYP2C9*3 and CYP2C9*3/*3 was observed in South Asian populations. Taken together, current study greatly enriches the knowledge of naturally occurring CYP2C9 variants and its diversity in South Asia, which are relevant to further CYP2C9-related functional research and for personalized medicine.

Cost Effectiveness of Genotype-Guided Antiplatelet Therapy in Asian Ischemic Stroke Patients: Ticagrelor as an Alternative to Clopidogrel in Patients with CYP2C19 Loss of Function Mutations

BACKGROUND

Patients with ischemic stroke are often treated with clopidogrel monotherapy as part of secondary stroke prevention. The prevalence of loss of function (LOF) mutations in the CYP2C19 gene is higher in Asians than in Western populations. Patients with loss of function (LOF) mutations are at risk for poorer secondary outcomes when prescribed clopidogrel.

OBJECTIVE

We aimed to determine the cost effectiveness of genotype-guided antiplatelet therapy in an Asian population with the aim of prescribing ticagrelor as an alternative to patients with LOF mutations.

METHODS

Markov models were developed to look at the cost effectiveness of genetic testing of CYP2C19, with patients who screened positive for LOF alleles being switched to ticagrelor compared to universal clopidogrel treatment. Effect ratios were obtained from the literature and incidence rates and costs were obtained from the national data published by the Singapore Ministry of Health. Lifetime costs and quality-adjusted life-years (QALYs) were calculated. The primary endpoints were the incremental cost-effectiveness ratios (ICERs).

RESULTS

The prevalence of the LOF mutations was 61% in the population, with 65% of ethnic Chinese, 60% of ethnic Indian, and 53% of ethnic Malay patients having LOF mutations. Based on this prevalence, the overall ICER of genetic testing was S$33,839/QALY with ICERS of S$30,755/QALY, S$33,177/QALY, and S$41,470/QALY for Chinese, Indians, and Malays, respectively.

CONCLUSION

This study suggests that it is cost effective to screen for LOF mutations in the CYP2C19 gene in ischemic stroke populations, with ticagrelor as a substitute for clopidogrel in those with LOF mutations.

Quantitative Systems Pharmacology Model-Based Predictions of Clinical Endpoints to Optimize Warfarin and Rivaroxaban Anti-Thrombosis Therapy

Background

Tight monitoring of efficacy and safety of anticoagulants such as warfarin is imperative to optimize the benefit-risk ratio of anticoagulants in patients. The standard tests used are measurements of prothrombin time (PT), usually expressed as international normalized ratio (INR), and activated partial thromboplastin time (aPTT).

Objective

To leverage a previously developed quantitative systems pharmacology (QSP) model of the human coagulation network to predict INR and aPTT for warfarin and rivaroxaban, respectively.

Methods

A modeling and simulation approach was used to predict INR and aPTT measurements of patients receiving steady-state anticoagulation therapy. A previously developed QSP model was leveraged for the present analysis. The effect of genetic polymorphisms known to influence dose response of warfarin (CYP2C9, VKORC1) were implemented into the model by modifying warfarin clearance (CYP2C9 *1: 0.2 L/h; *2: 0.14 L/h, *3: 0.04 L/h) and the concentration of available vitamin K (VKORC1 GA: −22% from normal vitamin K concentration; AA: −44% from normal vitamin K concentration). Virtual patient populations were used to assess the ability of the model to accurately predict routine INR and aPTT measurements from patients under long-term anticoagulant therapy.

Results

The introduced model accurately described the observed INR of patients receiving long-term warfarin treatment. The model was able to demonstrate the influence of genetic polymorphisms of CYP2C9 and VKORC1 on the INR measurements. Additionally, the model was successfully used to predict aPTT measurements for patients receiving long-term rivaroxaban therapy.

Conclusion

The QSP model accurately predicted INR and aPTT measurements observed during routine therapeutic drug monitoring. This is an exemplar of how a QSP model can be adapted and used as a model-based precision dosing tool during clinical practice and drug development to predict efficacy and safety of anticoagulants to ultimately help optimize anti-thrombotic therapy.

Effects of antifungal stewardship using therapeutic drug monitoring in voriconazole therapy on the prevention and control of hepatotoxicity and visual symptoms: A multicentre study conducted in Japan

Background

Hepatotoxicity and visual symptoms are common adverse effects (AEs) of voriconazole therapy.

Objective

To retrospectively evaluate the effects of treatment modification based on therapeutic drug monitoring on AEs in patients undergoing voriconazole therapy.

Methods

The target voriconazole trough concentration (C_min) was 1‐5 µg/mL. Receiver operating characteristic curves were used to determine C_min cut‐offs for AEs.

Results

A total of 401 patients were included. Among 108 patients with high initial C_min, voriconazole was discontinued in 32 and the dose was reduced in 71. Among 44 patients with low initial C_min, voriconazole was discontinued in 4 and the dose was increased in 19. Hepatotoxicity occurred in 6.0% of patients, after a median of 10 days. Visual symptoms were evident in 9.5% of patients after a median of 4 days. Initial C_min was significantly associated with visual symptoms but not hepatotoxicity, which suggested the effect of treatment modification on hepatotoxicity. However, both hepatotoxicity and visual symptoms were significantly correlated with C_min at the onset of AEs, and the C_min cut‐offs were 3.5 μg/mL for hepatotoxicity and 4.2 μg/mL for visual symptoms. Voriconazole was discontinued after the occurrence of AEs in 62.5% of patients with hepatotoxicity but only 26.3% of patients with visual symptoms. With dose adjustment, treatment was completed in 8/9 patients with hepatotoxicity and 27/28 patients with visual symptoms.

Conclusions

A significant preventive effect was demonstrated on hepatotoxicity, but not on visual symptoms because of earlier occurrence. With treatment modification after the occurrence of AEs, most patients completed therapy.

The Effect of CYP2C9 Genotype Variants in Type 2 Diabetes on the Pharmacological Effectiveness of Sulfonylureas, Diabetic Retinopathy, and Nephropathy

Aim

Type 2 diabetes (T2D), as a major cause of morbidity and mortality, is predicted to have a prevalence of 629 million by 2045. As diabetic patients show considerable inter-individual variation in response to antidiabetic treatment, this study aimed to investigate the gene polymorphism of cytochrome P450 as well as the effectiveness and safety of glibenclamide and gliclazide for different genotypes of CYP2C9. Besides, the chronic side effects of T2D including retinal microvasculature complications or retinopathy and renal dysfunction due to nephropathy in different genotypes were considered.

Patients and Methods

The participants including 80 T2D patients treated with glibenclamide or gliclazide were recruited from university hospitals of Ahvaz Jundishpur University of Medical Sciences, Ahvaz, in the southwest of Iran. Blood samples were collected from the patients at 2.5h after the morning dose of glibenclamide and 12h after the last dose of gliclazide. Genotyping from the extracted DNA was, then, performed using PCR-RFLP. The plasma level of glibenclamide and gliclazide was, in turn, measured by the reverse-phase high-pressure liquid chromatography.

Results

The results showed that the wild-type allele, i.e., CYP2C9*1, occurred in the highest frequency (0.8), while the frequency rates of the mutant allele, i.e., CYP2C9*2 and CYP2C9*3, were 0.15 and 0.05, respectively. Moreover, no significant association was found between any of the genotypes as well as the clinical and biochemical characteristics of the patients. The findings also showed that the plasma level of sulfonylureas (i.e., glibenclamide and gliclazide) was the highest in the patients with the CYP2C9*3 allele. It was also found that 75.9% of the patients with variant genotypes had experienced hypoglycemia events. Furthermore, in the absence of wild type allele, a significant increase was observed in retinopathy (p=0.039) and nephropathy (p=0.05).

Conclusion

The findings can provide guidelines for the optimal management of the treatment protocols with sulfonylurea intended to control the T2D complications.

Brazilian cohort and genes encoding for drug-metabolizing enzymes and drug transporters

Background & aim: Genetic variability in drug absorption, distribution, metabolism and excretion (ADME) genes contributes to the high heterogeneity of drug responses. The present study investigated polymorphisms of ADME genes frequencies and compared the findings with populations from other continents, available in the 1000 Genome Project (1 KGP) and the Exome Aggregation Consortium (ExAC) databases. Methodology & results: We conducted a study of 100 patients in Brazil and a total of 2003 SNPs were evaluated by targeted next-generation sequencing in 148 genes, including Phase I enzymes (n = 50), Phase II enzymes (n = 38) and drug transporters (n = 60). Overall, the distribution of minor allele frequency (MAF) suggests that the distribution of 2003 SNPs is similar between Brazilian cohort, 1 KGP and ExAC; however, we found moderate SNP allele-frequency divergence between Brazilian cohort and both 1000 KGP and ExAC. These differences were observed in several relevant genes including CYP3A4, NAT2 and SLCO1B1. Conclusion: We concluded that the Brazilian population needs clinical assessment of drug treatment based on individual genotype rather than ethnicity.

Utility of CT assessment in hematology patients with invasive aspergillosis: a post-hoc analysis of phase 3 data

BACKGROUND

Pulmonary computed tomography (CT) scans are commonly used as part of the clinical criteria in diagnostic workup of invasive fungal diseases like invasive aspergillosis, and may identify radiographic abnormalities, such as halo signs or air-crescent signs. We assessed the diagnostic utility of CT assessment in patients with hematologic malignancies or those who had undergone allogeneic hematopoietic stem cell transplantation in whom invasive aspergillosis was suspected.

METHODS

This post-hoc analysis assessed data from a prospective, multicenter, international trial of voriconazole (with and without anidulafungin) in patients with suspected invasive aspergillosis (IA; proven, probable, or possible, using 2008 European Organisation for Research and Treatment of Cancer/Invasive Fungal Infections Cooperative Group and the National Institute of Allergy and Infectious Diseases Mycoses Study Group criteria) [NCT00531479]. Eligible patients received at least one baseline lung CT scan.

RESULTS

Of 395 patients included in this post-hoc analysis, 240 patients (60.8%) had 'confirmed' proven (9/240, 3.8%) or probable (231/240, 96.3%) invasive aspergillosis (cIA) and 155 patients (39.2%) had 'non-confirmed' invasive aspergillosis (all nIA; all possible IA (de Pauw et al., Clin Infect Dis 46:1813-21, 2008)). Mean age was 52.3 and 50.5 years, 56.3 and 60.0% of patients were male, and most patients were white (71.7 and 71.0%) in the cIA and nIA populations, respectively. Median baseline galactomannan was 1.4 (cIA) and 0.2 (nIA), mean Karnofsky score was 65.3 (cIA) and 66.8 (nIA), and mean baseline platelet count was 48.0 (cIA) and 314.1 (nIA). Pulmonary nodules (46.8% of all patients), bilateral lung lesions (37.5%), unilateral lung lesions (28.4%), and consolidation (24.8%) were the most common radiographic abnormalities. Ground-glass attenuation (cIA: 24.2%; nIA: 11.6%; P < 0.01) and pulmonary nodules (cIA: 52.5%; nIA: 38.1%; P < 0.01) were associated with cIA. Other chest CT scan abnormalities (including halo signs and air-crescent signs) at baseline in patients with hematologic malignancy or hematopoietic stem cell transplantation, and suspected IA, were not associated with cIA.

CONCLUSIONS

These findings highlight the limitations in the sensitivity of chest CT scans for the diagnosis of IA, and reinforce the importance of incorporating other available clinical data to guide management decisions on individual patients, including whether empirical treatment is reasonable, pending full evaluation.

TRIAL REGISTRATION

NCT00531479 (First posted on ClinicalTrials.gov on September 18, 2007).

Evaluating a voriconazole dose modification guideline to optimize dosing in patients with hematologic malignancies

BACKGROUND

Voriconazole is an azole antifungal utilized for prophylaxis and treatment of invasive fungal infections in hematologic patients. Previous studies have revealed decreased efficacy and increased toxicity with subtherapeutic <1 mcg/mL and supratherapeutic > 4 mcg/mL levels. A voriconazole dose modification guideline was introduced in July 2014 based on a retrospective analysis.

OBJECTIVE

The primary objective was to evaluate the voriconazole dose modification guideline. Secondary objectives were to identify patient-specific characteristics that contribute to inadequate levels, adverse effects, and breakthrough invasive fungal infections.

METHODS

This prospective study included 128 patients with 250 admissions who received voriconazole from July 2014 to February 2016. Eligible adult patients receiving voriconazole for prophylaxis or treatment with at least one trough level, drawn appropriately, were included. Demographics, adverse effects, and breakthrough invasive fungal infections were documented.

RESULTS

Voriconazole use was categorized as: new start, new start with loading dose, or continuation of home therapy. The median initial levels were 1.5, 3.5, and 1.7 mcg/mL with 62% (73/119), 55% (6/11), and 60% (72/120) within the therapeutic range, respectively. Using the voriconazole dose modification guideline, 80% were within goal by the second dose adjustment. Age ≤ 30 and BMI ≤ 25 kg/m² had higher rates of subtherapeutic levels in the new start cohorts (p = 0.024 and p = 0.009). Approximately 7.6% of patients experienced an adverse effect with neurologic/psychological being the most common. A total of 8.5% of patients had a possible, probable or proven breakthrough invasive fungal infections while on voriconazole.

CONCLUSION

Using the voriconazole dose modification guideline, the number of patients that reached therapeutic range improved from 36% to 80% by the second dose adjustment (p = 0.007). This voriconazole dose modification guideline can be utilized to help dose and adjust voriconazole in order to achieve therapeutic levels.

CYP2C9 polymorphisms in epilepsy: influence on phenytoin treatment

Phenytoin (PHT) is an antiepileptic drug widely used in the treatment of focal epilepsy and status epilepticus, and effective in controlling focal seizures with and without tonic-clonic generalization and status epilepticus. The metabolization of PHT is carried out by two oxidative cytochrome P450 enzymes CYP2C9 and CYP2C19; 90% of this metabolization is done by CYP2C9 and the remaining 10% by CYP2C19. Genetic polymorphism of CYP2C9 may reduce the metabolism of PHT by 25-50% in patients with variants *2 and *3 compared to those with wild-type variant *1. The frequency distribution of CYP2C9 polymorphism alleles in patients with epilepsy around the world ranges from 4.5 to 13.6%, being less frequent in African-Americans and Asians. PHT has a narrow therapeutic range and a nonlinear pharmacokinetic profile; hence, its poor metabolization has significant clinical implications as it causes more frequent and more serious adverse effects requiring discontinuation of treatment, even if it had been effective. There is evidence that polymorphisms of CYP2C9 and the use of PHT are associated with an increase in the frequency of some side effects, such as cerebellar atrophy, gingival hypertrophy or acute cutaneous reactions. The presence of HLA-B*15:02 and CYP2C9 *2 or *3 in the same patient increases the risk of Stevens-Johnson syndrome and toxic epidermal necrolysis; hence, PHT should not be prescribed in these patients. In patients with CYP2C9 *1/*2 or *1/*3 alleles (intermediate metabolizers), the usual PHT maintenance dose (5-10 mg/kg/day) must be reduced by 25%, and in those with CYP2C9 *2/*2, *2/*3 or *3/*3 alleles (poor metabolizers), the dose must be reduced by 50%. It is controversial whether CYP2C9 genotyping should be done before starting PHT treatment. In this paper, we aim to review the influence of CYP2C9 polymorphism on the metabolization of PHT and the clinical implications of poor metabolization in the treatment of epilepsies.

Efficacy and Safety Profile of Z-215 (Azeloprazole Sodium), a Proton Pump Inhibitor, Compared with Rabeprazole Sodium in Patients with Reflux Esophagitis: A Phase II, Multicenter, Randomized, Double-Blind, Comparative Study

BACKGROUND

The metabolism of many proton pump inhibitors is influenced by CYP2C19 genotype, which is a limitation of their use.

OBJECTIVES

To determine the efficacy and safety profile of Z-215 (azeloprazole sodium) as initial treatment for reflux esophagitis (RE), dose response, and optimal dose compared with rabeprazole sodium (RPZ).

METHODS

We conducted an exploratory, multicenter, randomized, double-blind, parallel-group study in Japan. Patients with RE aged ≥20 years were enrolled and randomly assigned to receive 10, 20, or 40 mg Z-215 or 10 mg RPZ (1:1:1:1), and orally administered the respective drug for 8 weeks. The primary efficacy end point was the endoscopic healing rate after 8 weeks of treatment (at Week 8). We also assessed the effects of CYP2C19 genotype. Safety end points were the incidence of adverse events and adverse drug reactions.

RESULTS

Five hundred three patients received the study drugs (10 mg Z-215: 125 patients, 20 mg Z-215: 126 patients, 40 mg Z-215: 126 patients, and 10 mg RPZ: 126 patients). The endoscopic healing rate at Week 8 was above 95% in all groups (10 mg Z-215: 95.2%, 20 mg Z-215: 96.8%, 40 mg Z-215: 95.2%, and 10 mg RPZ: 96.8%). The endoscopic healing rate and serum gastrin levels of the Z-215 groups were not influenced by CYP2C19 genotype. In patients with Grade C/D, the endoscopic healing rate at Week 4 was slightly higher in the 40-mg Z-215 group compared with the other groups. Incidences of adverse events/adverse drug reactions did not markedly differ between the Z-215 and 10-mg RPZ groups.

CONCLUSIONS

Z-215 was as effective and well tolerated as 10 mg RPZ in the treatment of RE in this selected population. CYP2C19 genotype status may not influence the efficacy and safety of Z-215. There were no clear dose-response effects between Z-215 doses in the endoscopic healing of RE. These findings suggest that Z-215 may be 1 option for the initial treatment of RE. ClinicalTrials.gov identifier: NCT 02463643.

A review of the pharmacology and clinical efficacy of brivaracetam

Brivaracetam (BRV; Briviact) is a new antiepileptic drug (AED) approved for adjunctive treatment of focal (partial-onset) seizures in adults. BRV is a selective, high-affinity ligand for synaptic vesicle 2A (SV2A) with 15- to 30-fold higher affinity than levetiracetam, the first AED acting on SV2A. It has high lipid solubility and rapid brain penetration, with engagement of the target molecule, SV2A, within minutes of administration. BRV has potent broad-spectrum antiepileptic activity in animal models. Phase I studies indicated BRV was well tolerated and showed a favorable pharmacokinetic profile over a wide dose range following single (10–1,000 mg) and multiple (200–800 mg/day) oral dosing. Three pivotal Phase III studies have demonstrated promising efficacy and a good safety and tolerability profile across doses of 50–200 mg/day in the adjunctive treatment of refractory focal seizures. Long-term data indicate that the response to BRV is sustained, with good tolerability and retention rate. BRV is highly effective in patients experiencing secondarily generalized tonic–clonic seizures. Safety data to date suggest a favorable psychiatric adverse effect profile in controlled studies, although limited postmarketing data are available. BRV is easy to use, with no titration and little drug–drug interaction. It can be initiated at target dose with no titration. Efficacy is seen on day 1 of oral use in a significant percentage of patients. Intravenous administration in a 2-minute bolus and 15-minute infusion is well tolerated. Here, we review the pharmacology, pharmacokinetics, and clinical data of BRV.

Genetic Polymorphisms of Cytochrome P450 Enzymes and Transport Proteins in a Russian Population and Three Ethnic Groups of Dagestan

AIM

The objective of this study was to investigate the prevalence of polymorphic markers of the CYP2C19, CYP2C9, CYP2D6, SLCO1B1, and ABCB1 genes among the three ethnic groups in Dagestan and compare it with the carrier frequency of these markers among the Russian population living in Moscow.

METHODS

The study involved 186 healthy, unrelated, and chronic medication-free volunteers (53 males and 133 females) of the three ethnic groups in the Dagestan Republic: 46 Laks, 90 Avars, and 50 Dargins. Genotyping was performed using real-time polymerase chain reaction-based methods. The allelic prevalences of the three Dagestan peoples were compared with ethnic Russians from the Moscow region.

RESULTS

Statistically significant differences for the following gene polymorphisms: CYP2C19*17, CYP2C9*3, ABCB1 (C3435T), SLCO1B1*5 were found between the Russian population and the three ethnic groups of the Dagestan republic.

CONCLUSION

The data obtained from this study will help with prioritization genotyping in the region.

Distribution of CYP2C8 and CYP2C9 amino acid substitution alleles in South Indian diabetes patients: A genotypic and computational protein phenotype study

The CYP2C8 and CYP2C9 are two major isoforms of the cytochrome P450 enzyme family, which is involved in drug response, detoxification, and disease development. This study describes the differential distribution of amino acid substitution variants of CYP2C8 (*2-I269F & *3-R139K) and CYP2C9 (*2-C144R & *3-L359A) genes in 234 type 2 diabetes mellitus (T2DM) patients and 218 healthy controls from Andhra Pradesh, South India. Single locus genotype analysis has revealed that homozygous recessive genotypes of 2C8*2-TT (P ≤ .03), 2C9*2-TT (P ≤ .02), and heterozygous 2C9*3-AC (P ≤ .006) are seen to be increasingly present in the case group, indicating a significant level of their association with diabetes in Andhra population. The statistical significance of these recessive genotypes has persisted even under their corresponding allelic forms (P ≤ .01). Genotype association results were further examined by computational protein structure and stability analysis to assess the deleteriousness of the amino acid changes. The mutant CYP 2C8 and 2C9 (both *2 and *3) proteins showed structural drifts at both amino acid residue (range 0.43Å-0.77Å), and polypeptide chain levels (range 0.68Å-1.81Å) compared to their wild-type counterparts. Furthermore, the free energy value differences (range -0.915 to -1.38 Kcal/mol) between mutant and native protein structures suggests the deleterious and destabilizing potential of amino acid substitution polymorphisms of CYP genes. The present study confirms the variable distribution of CYP2C8 (*2 and *3) and CYP2C9 (*2 and *3) allelic polymorphisms among South Indian diabetic populations and further warrants the serious attention of CYP gene family, as a putative locus for disease risk assessment and therapy.

Co-administration of proton pump inhibitors ameliorates nephrotoxicity in patients receiving chemotherapy with cisplatin and fluorouracil: a retrospective cohort study

PURPOSE

The nephrotoxicity of cisplatin (CDDP) is its dose-limiting side effect, and is caused by renal accumulation of CDDP mainly via organic cation transporter 2 (OCT2). Because proton pump inhibitors (PPIs) are known to inhibit OCT2 activity, PPI might ameliorate CDDP-induced nephrotoxicity. In the present study, we retrospectively investigated the effect of co-administration of PPI on CDDP-induced nephrotoxicity.

METHODS

We analyzed the impact of PPI on the development of nephrotoxicity in 133 patients who received CDDP and fluorouracil (5-FU) therapy for the treatment of esophageal cancer or head and neck cancer. Nephrotoxicity that developed within 14 days following CDDP administration was evaluated in accordance with Common Terminology Criteria for Adverse Events ver. 4.0 for acute kidney injury.

RESULTS

The rate of nephrotoxicity in patients with PPI (12%, n = 33) was significantly lower than that in patients without PPI (30%, n = 100). Severe nephrotoxicity greater than Grade 2 was not observed in patients with PPI, whereas the rate of hematological toxicity was comparable between patients with and without PPI. Kaplan-Meier analysis showed that the time to nephrotoxicity following CDDP administration was significantly prolonged in patients with PPI. Multivariate analysis revealed that co-administration of PPI with CDDP and 5-FU was an independent factor significantly contributing to the amelioration of nephrotoxicity (odds ratio 0.239, p = 0.033).

CONCLUSIONS

These findings indicate that co-administration of clinical doses of PPI could ameliorate nephrotoxicity without exacerbation of hematological toxicity in patients receiving CDDP and 5-FU therapy.

CYP2C9, CYPC19 and CYP2D6 gene profiles and gene susceptibility to drug response and toxicity in Turkish population

Pharmacogenetics is a vast field covering drug discovery research, the genetic basis of pharmacokinetics and dynamics, genetic testing and clinical management in diseases. Pharmacogenetic approach usually focuses on variations of drug transporters, drug targets, drug metabolizing enzymes and other biomarker genes. Cytochrome P450 (CYP) enzymes, an essential source of variability in drug-response, play role in not only phase I-dependent metabolism of xenobiotics but also metabolism of endogenous compounds such as steroids, vitamins and fatty acids. CYP2C9, CYP2C19 and CYP2D6 enzymes being highly polymorphic are responsible for metabolism of a variety of drug groups. In the study, it was determined the genotype and allele frequency of CYP2C9∗2, CYP2C19∗3, CYP2C19∗2, CYP2C19∗3, CYP2C19∗17, CYP2D6∗9 and CYP2D6∗41, very common and functional single-nucleotide polymorphisms (SNPs), in healthy volunteers. The genotype distributions were consistent with the Hardy-Weinberg equilibrium in the population (p > 0.05). It is believed that the determination of polymorphisms in the enzymes may be beneficial in order to prevention or reduction in adverse effects and death. The recessive allele frequencies of CYP2C9∗2, CYP2C19∗3, CYP2C19∗2, CYP2C19∗3, CYP2C19∗17, CYP2D6∗9 and CYP2D6∗41 were 11, 13, 12, 13, 25, 4 and 15%, respectively. According to the obtained results, the carriers of CYP2D6∗9 variant allele should be received higher doses of the drugs metabolizing with this enzyme in Turkish population, while the carriers of other variant alleles do not generally have any requirement of dose regimen.

Different effects of lansoprazole and rabeprazole on the plasma voriconazole trough levels in allogeneic hematopoietic cell transplant recipients

Voriconazole (VRC) is widely used as prophylaxis and in the treatment of invasive fungal disease (IFD) after allogeneic hematopoietic cell transplantation (HCT). We retrospectively examined the results of VRC therapeutic drug monitoring (TDM) in allogeneic HCT recipients. A total of 474 samples were obtained from 59 adult patients who received VRC during the first 100 days following HCT between 2009 and 2014 in our institute. Seventeen patients received VRC for prophylaxis of IFD, and 42 received VRC for the empirical or preemptive therapy for IFD. A total of 299 samples (63 %) were obtained during the administration of the intravenous form of VRC. The median VRC daily dose based on the actual body weight was 6.68 mg/kg/day (range, 1.92-10.41 mg/kg/day). The median VRC trough level was 0.99 mg/l (range, <0.09-5.45 mg/l). The multivariate analysis using a logistic regression model demonstrated significantly higher VRC trough levels (≥1.0 mg/l) in males (P < 0.001), empirical or preemptive therapy (P = 0.002), VRC daily dose based on the actual body weight ≥7 mg/kg/day (P < 0.001), and concomitant use of lansoprazole as compared to rabeprazole (P < 0.001). The concomitant use of calcineurin inhibitors and corticosteroids had no effects on VRC trough levels in multivariate analysis. These data suggest that lansoprazole and rabeprazole have different effects on the plasma VRC trough levels in the allogeneic HCT recipients.

Lansoprazole Exacerbates Pemetrexed-Mediated Hematologic Toxicity by Competitive Inhibition of Renal Basolateral Human Organic Anion Transporter 3

Pemetrexed, a multitargeted antifolate, is eliminated by tubular secretion via human organic anion transporter 3 (hOAT3). Although proton pump inhibitors (PPIs) are frequently used in cancer patients, the drug interaction between PPIs and pemetrexed remains to be clarified. In this study, we examined the drug interaction between pemetrexed and PPIs in hOAT3-expressing cultured cells, and retrospectively analyzed the impact of PPIs on the development of hematologic toxicity in 108 patients who received pemetrexed and carboplatin treatment of nonsquamous non-small cell lung cancer for the first time between January 2011 and June 2015. We established that pemetrexed was transported via hOAT3 (Km = 68.3 ± 11.1 µM). Lansoprazole, rabeprazole, pantoprazole, esomeprazole, omeprazole, and vonoprazan inhibited hOAT3-mediated uptake of pemetrexed in a concentration-dependent manner. The inhibitory effect of lansoprazole was much greater than those of other PPIs and the apparent IC50 value of lansoprazole against pemetrexed transport via hOAT3 was 0.57 ± 0.17 µM. The inhibitory type of lansoprazole was competitive. In a retrospective study, multivariate analysis revealed that coadministration of lansoprazole, but not other PPIs, with pemetrexed and carboplatin was an independent risk factor significantly contributing to the development of hematologic toxicity (odds ratio: 10.004, P = 0.005). These findings demonstrated that coadministration of lansoprazole could exacerbate the hematologic toxicity associated with pemetrexed, at least in part, by competitive inhibition of hOAT3. Our results would aid clinicians to make decisions of coadministration drugs to avoid drug interaction-induced side effects for achievement of safe and appropriate chemotherapy with pemetrexed.

Pharmacogenomic Effect of Cytochrome P450 2C9 Polymorphisms in Different Populations

Presently, warfarin sodium or coumadin is the therapeutic drug of choice for maintenance anticoagualtion therapy. One of several factors underlying the variability in warfarin dose response in the patients receiving this oral anticoagulant is a genetic predisposition, especially the CYP2C9 polymorphisms. The pharmacogenomic effect of CYP2C9 polymorphisms is assessed in different racial populations. A retrospective review was performed with an electronic search engine on this topic to get the data for further meta-analysis. A significant correlation between population ethnicity and gene frequencies was detected in this study. A significant low frequency of CYP2C9 variants among the Asian can be demonstrated. The clinical correlation between CYP2C9 polymorphism and warfarin metabolism was also assessed. Four available case-control reports were selected for this meta-analysis. CYP2C9 variants are strongly associated with low-dose warfarin requirement. In summary, the CYP2C9 variants strongly affect the warfarin dose requirement. This phenomenon is ethnically dependent. Due to the high variant frequency among whites in the West, the investigation for CYP2C9 might be useful for this population, not the Asians, whose variant frequency is very low.

Systematic characterization and comparison of the CYP2C9 variability of the Orang Asli in Malaysia with 12 populations

We conducted a systematic characterization of CYP2C9 variants in 61 Orang Asli and 96 Singaporean Malays using the whole genome sequences data and compared the variants with the other 11 HapMap populations. The frequency of rs1057910 (CYP2C9*3) is the highest in the Orang Asli compared to other populations. Three alleles with clinical implication were detected in the Orang Asli while 2 were found in the Singaporean Malays. Large numbers of the Orang Asli are predicted to have reduced metabolic capacity and therefore they would require a lower dose of drugs which are metabolized by CYP2C9. They are also at increased risks of adverse effects and therapeutic failures. A large number of CYP2C9 variants in the Orang Asli were not in the Hardy Weinberg Equilibrium which could be due to small sample size or mutations that disrupt the equilibrium of allele frequencies. In conclusion, different polymorphism patterns, allele frequencies, genotype frequencies and LD blocks are observed between the Orang Asli, the Singaporean Malays and the other populations. The study provided new information on the genetic polymorphism of CYP2C9 which is important for the implementation of precision medicine for the Orang Asli.

Therapeutic drug monitoring of voriconazole in Japanese patients: analysis based on clinical practice data

The aim of this study was to investigate whether routine therapeutic drug monitoring (TDM) of voriconazole (VRCZ) reduced discontinuation due to hepatotoxicity. Hepatotoxicity was observed in 15 (51.7%) out of 29 patients. The percentages of patients who developed hepatotoxicity within 4 days and 1 week were 26.7 and 46.7%, respectively. The drug trough concentrations in patients with and without hepatotoxicity were 5.55 ± 2.73 and 2.36 ± 1.67 μg/ml (P < 0.01, the two-sided Student's t-test), respectively. Trough concentrations reached the target of 1-5 μg/ml in patients with gradual dose reductions based on TDM, and, consequently, liver enzyme levels returned to the original levels before the VRCZ treatment. All patients eventually continued effective VRCZ therapy despite its hepatotoxicity. Thus, dose adjustments by TDM to achieve the target trough concentrations is useful in order to avoid hepatotoxicity and enable continued effective VRCZ therapy for Japanese patients with invasive fungal infections.

Genotype‑phenotype analysis of CYP2C19 in the Tibetan population and its potential clinical implications in drug therapy

Cytochrome P450 2C19 (CYP2C19) is a highly polymorphic gene, it codes for a protein responsible for the metabolism of multiple clinically important therapeutic agents. However, there is currently no available data on the distribution of CYP2C19 mutant alleles in the Tibetan population. The aim of the present study was to identify different CYP2C19 mutant alleles and determine their frequencies, along with genotypic frequencies, in the Tibetan population. The whole CYP2C19 gene was amplified and sequenced in 96 unrelated, healthy Tibetans from the Tibet Autonomous Region of China, the promoter region, exons, introns and the 3'‑UTR were screened for genetic variants. Three novel genetic polymorphisms in CYP2C19 were detected among a total of 27 different mutations. The allele frequencies of CYP2C19*1A, *1B, *2A, *3A and *17 were 50, 28.13, 15.10, 5.21 and 1.56%, respectively. The most common genotype combinations were CYP2C19*1A/*1B (56.25%) and *1A/*2A (30.21%). One novel non‑synonymous mutation (Asn to Lys) in CYP2C19 was identified, and this mutation was predicted to be intolerant and benign by SIFT and PolyPhen‑2, respectively. The observations of the present study may have important clinical implications for the use of medications metabolized by CYP2C19 among Tibetans.

Interethnic variation of CYP2C19 alleles, 'predicted' phenotypes and 'measured' metabolic phenotypes across world populations

The present study evaluates the worldwide frequency distribution of CYP2C19 alleles and CYP2C19 metabolic phenotypes ('predicted' from genotypes and 'measured' with a probe drug) among healthy volunteers from different ethnic groups and geographic regions, as well as the relationship between the 'predicted' and 'measured' CYP2C19 metabolic phenotypes. A total of 52 181 healthy volunteers were studied within 138 selected original research papers. CYP2C19*17 was 42- and 24-fold more frequent in Mediterranean-South Europeans and Middle Easterns than in East Asians (P<0.001, in both cases). Contrarily, CYP2C19*2 and CYP2C19*3 alleles were more frequent in East Asians (30.26% and 6.89%, respectively), and even a twofold higher frequency of these alleles was found in Native populations from Oceania (61.30% and 14.42%, respectively; P<0.001, in all cases), which may be a consequence of genetic drift process in the Pacific Islands. Regarding CYP2C19 metabolic phenotype, poor metabolizers (PMs) were more frequent among Asians than in Europeans, contrarily to the phenomenon reported for CYP2D6. A correlation has been found between the frequencies of CYP2C19 poor metabolism 'predicted' from CYP2C19 genotypes (gPMs) and the poor metabolic phenotype 'measured' with a probe drug (mPMs) when subjects are either classified by ethnicity (r=0.94, P<0.001) or geographic region (r=0.99, P=0.002). Nevertheless, further research is needed in African and Asian populations, which are under-represented, and additional CYP2C19 variants and the 'measured' phenotype should be studied.

Comparison of micafungin and voriconazole as empirical antifungal therapies in febrile neutropenic patients with hematological disorders: a randomized controlled trial

OBJECTIVES

In cases of hematological malignancy, patients with persistent fever and neutropenia receive antifungal empirical therapy to prevent and treat invasive fungal infections. The clinical efficacy and safety of micafungin and voriconazole were compared.

METHODS

In this randomized, cooperative group, open-label trial, we assessed and compared the efficacy and safety of micafungin and voriconazole as an empirical antifungal therapy in febrile neutropenic patients with hematological malignancy. Patients were classified according to invasive fungal infection risk.

RESULTS

There were no significant differences in clinical efficacy between the two treatments, evaluated based on (i) successful treatment of baseline fungal infection (no evaluation), (ii) absence of breakthrough fungal infection (P = 0.106), (iii) survival for ≥7 days after study completion (P = 0.335), (iv) premature study discontinuation due to poor efficacy (P = 0.424), and (v) resolution of fever during neutropenia (P = 0.756). Discontinuation due to drug-related adverse events (grades 3-4) occurred less frequently in the micafungin group (P = 0.005).

CONCLUSIONS

The clinical efficacy did not differ between micafungin and voriconazole. Micafungin was generally better tolerated than voriconazole when given as an empirical antifungal therapy in patients with persistent fever and neutropenia.

Therapeutic drug monitoring for triazoles: A needs assessment review and recommendations from a Canadian perspective

Invasive fungal infections cause significant morbidity and mortality in patients with concomitant underlying immunosuppressive diseases. The recent addition of new triazoles to the antifungal armamentarium has allowed for extended-spectrum activity and flexibility of administration. Over the years, clinical use has raised concerns about the degree of drug exposure following standard approved drug dosing, questioning the need for therapeutic drug monitoring (TDM). Accordingly, the present guidelines focus on TDM of triazole antifungal agents. A review of the rationale for triazole TDM, the targeted patient populations and available laboratory methods, as well as practical recommendations based on current evidence from an extended literature review are provided in the present document.

Cytochrome P450 genetic polymorphisms of Mexican indigenous populations

This review focuses on the genetic polymorphisms of the cytochrome P450 (CYP) genes in Mexican indigenous populations, who are a part of the wide ethnic diversity of this country. These native groups have a particular historical trajectory that is different from the Mexican Mestizos. This variability may be reflected in the frequency distribution of polymorphisms in the CYP genes that encode enzymes involved in the metabolism of drugs and other xenobiotics. Therefore, these polymorphisms may affect drug efficacy and safety in indigenous populations in Mexico. The present study aimed to analyze the prevalence of CYP polymorphisms in indigenous Mexicans and to compare the results with studies in Mexican Mestizos. Because the extrapolation of pharmacogenetic data from Mestizos is not applicable to the majority of indigenous groups, pharmacogenetic studies directed at indigenous populations need to be developed. The Amerindians analyzed in this study showed a low phenotypic (CYP2D6) and genotypic (CYP2D6, CYP2C9) diversity, unlike Mexican Mestizos. The frequency of polymorphisms in the CYP1A1, CYP2C19, CYP2E1, and CYP3A4 genes was more similar among the Amerindians and Mexican Mestizos, with the exception of the CYP1A2 gene, whose *1F variant frequency in Mexican Amerindians was the highest described to date.

Genetic epidemiology of pharmacogenetic variations in CYP2C9, CYP4F2 and VKORC1 genes associated with warfarin dosage in the Indian population

Aim: Warfarin, a widely used anticoagulant, exhibits large interindividual variability in dose requirements. CYP2C9 and VKORC1 polymorphisms in various ethnic groups have been extensively studied as genetic markers associated with variable drug response. However, allele frequencies of these variants have not been assessed in major ethnic groups in the Indian population. Materials & methods: To study the functional variants known to affect warfarin dosing, we reanalyzed genotype microarray datasets generated as a part of genome-wide association studies as well as data from the Indian Genome Variation database. We examined data from 2680 individuals across 24 ethnically diverse Indian subpopulations. Results: Allelic distribution of VKORC1 (-1639G>A) showed a greater degree of variation across Indian subpopulations, with frequencies as low as 6.5% in an out-group subpopulation to >70% in Tibeto–Burmans. Risk allele frequency of CYP4F2*3 (V433M) was higher in north Indians (0.30–0.44), as compared with other world populations, such as African–American (0.12), Caucasian (0.34) and Hispanic (0.23). TheVKORC1 variant (-1639A) was shown to be prevalent amongst Tibeto–Burmans, whereas CYP2C9 (R144C, I359L) and CYP4F2 (V433M) variants were observed in considerable variability amongst Indo–Europeans. The frequency of CYP2C9*3 (I359L) in north Indians was found to be higher than in most Asian populations. Furthermore, geographical distribution patterns of these variants in north India showed an increased trend of warfarin extensive metabolizers from the Himalayan to Gangetic region. Combined allele frequency (CYP2C9*3 and CYP4F2*3) data suggest that poor metabolizers varied in the range of 0.38–1.85% in Indo–Europeans. Conclusion: Based on genotypic distribution, the majority of the Indian subpopulation might require higher doses for stable anticoagulation, whereas careful assessment is required for Tibeto–Burmans who are expected to have intermediate dose requirement. This is the largest global genetic epidemiological study examining variants associated with warfarin that could potentially be valuable to clinicians in optimizing dosage strategies.

Original submitted 4 April 2014; Revision submitted 23 May 2014

Brivaracetam single and multiple rising oral dose study in healthy Japanese participants: influence of CYP2C19 genotype

Brivaracetam is a high-affinity synaptic vesicle protein 2A ligand, in phase 3 clinical development for epilepsy. A phase 1, single-center, randomized, double-blind, placebo-controlled, single (2.5-100 mg) and multiple (2.5-50 mg twice daily) rising oral dose study (N01209) was conducted to assess the adverse event profile and pharmacokinetics of brivaracetam in healthy Japanese men, and the influence of the cytochrome P450 (CYP) 2C19 genotype. Plasma and urine were collected serially for analysis of brivaracetam and its three main metabolites: acid, hydroxy and hydroxy acid. Overall, 79/80 randomized participants completed the study. Brivaracetam was generally well tolerated. After single- and multiple-dose administration, brivaracetam was rapidly absorbed, with dose-proportional pharmacokinetics over the dose ranges tested. Steady state was reached after 2 days of repeated dosing. Brivaracetam clearance (averaged across the five single dose levels) was reduced from 0.99 mL/min/kg in homozygous extensive metabolizers (EM; n = 10) to 0.81 mL/min/kg (-18%) in heterozygous EM (n = 17) and 0.70 mL/min/kg (-29%) in poor metabolizers (PM; n = 9). Exposure and urinary excretion of hydroxy metabolite were reduced 10-fold in PM participants, compared with EM participants. Results suggest that brivaracetam is hydroxylated by CYP2C19, but this pathway is minor compared with hydrolysis to the acid metabolite.

A High-Throughput (HTS) Assay for Enzyme Reaction Phenotyping in Human Recombinant P450 Enzymes Using LC-MS/MS

Enzyme reaction phenotyping is employed extensively during the early stages of drug discovery to identify the enzymes responsible for the metabolism of new chemical entities (NCEs). Early identification of metabolic pathways facilitates prediction of potential drug-drug interactions associated with enzyme polymorphism, induction, or inhibition, and aids in the design of clinical trials. Incubation of NCEs with human recombinant enzymes is a popular method for such work because of the specificity, simplicity, and high-throughput nature of this approach for phenotyping studies. The availability of a relative abundance factor and calculated intersystem extrapolation factor for the expressed recombinant enzymes facilitates easy scaling of in vitro data, enabling in vitro-in vivo extrapolation. Described in this unit is a high-throughput screen for identifying enzymes involved in the metabolism of NCEs. Emphasis is placed on the analysis of the human recombinant enzymes CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2B6, and CYP3A4, including the calculation of the intrinsic clearance for each.

[The development of appropriate dosage of anti-bacterial and anti-fungal agents based on pharmacokinetics and pharmacodynamics]

An initial loading procedure has been recommended to enable teicoplanin to promptly reach an effective serum concentration for the treatment of methicillin-resistant Staphylococcus aureus (MRSA). The mean trough concentrations were 13.2 mg/L for patients with eradication of MRSA. I showed that the administration of ≥36 mg/kg during the first 3 days was effective in promptly obtaining a trough concentration target of ≥13 mg/L for the initial treatment of MRSA infections. The major adverse effect associated with linezolid treatment is reversible myelosuppression, primarily thrombocytopenia. I demonstrated that the incidence of linezolid-induced thrombocytopenia was higher among patients with renal failure than in patients with normal renal function. A statistically significant (p<0.01) and strong correlation (r=0.933) was observed between linezolid and creatinine clearance. A negative correlation (r=-0.567) was also shown between linezolid clearance and blood urea nitrogen. Voriconazole trough plasma concentration has been reported to correlate with hepatotoxicity. Logistic regression analysis revealed that the therapeutic range for the voriconazole trough concentration should be 2-4 mg/L. Nonlinear 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 4.4-6.5 mg/kg/day for the non-wild type in patients. Anaemia and thrombocytopenia are major side effects of liposomal amphotericin B. I demonstrated that the doses of liposomal amphotericin B estimated to cause side effects of a low red blood cell count, anaemia and thrombocytopenia with 50% probability are 4.0, 3.3 and 3.0 mg/kg/day, respectively.

Analysis of CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A polymorphisms in a population from South-Eastern Europe

The CYP2C9 enzyme metabolizes a wide range of relevant drugs, among which are oral anticoagulants. VKORC1 is the pharmacodynamic target of the oral anticoagulants. The genetic polymorphisms CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A are the major determinants of the inter-individual variability in the dosage requirements of oral anticoagulants. This study provides a first evaluation of these 3 polymorphisms in a Romanian population. A total of 332 Romanian individuals were genotyped for the CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A polymorphisms using the PCR-RFLP technique. Sixty-two individuals (18.7%) were heterozygous for CYP2C9*2, whereas 47 individuals (14.1%) were heterozygous for CYP2C9*3. Fourteen individuals (4.2%) had a CYP2C9*2 homozygous, CYP2C9*3 homozygous or CYP2C9*2/CYP2C9*3 compound heterozygous genotype. These individuals are predicted to have the lowest CYP2C9 enzymatic activity. The allele frequencies of the CYP2C9*2 and CYP2C9*3 polymorphisms were 11.3% and 9.3% respectively. For the VKORC1 -1639 G>A polymorphism, there were 170 heterozygotes (51.2%) and 55 (16.6%) homozygotes for the A allele. The frequency of the A allele was 42.2%. Overall, the distribution of the CYP2C9*2, CYP2C9*3 and VKORC1 -1639 G>A polymorphisms observed in our cohort is in accordance with other Caucasian populations. A large number of Romanians are expected to harbour at least one CYP2C9 variant allele and/or one VKORC1 -1639 G>A allele. This frequency has major implications in the pharmacogenomics of oral anticoagulants in Romanians.

Detection of cytochrome P450 2C19 gene polymorphism from noninvasive samples by cycling probe technology

Background

The proportion of poor metabolizers (PMs) of cytochrome P450 (CYP) 2C19 is much higher in the Japanese population than in European populations. Cycling probe technology (CPT) is a simple signal amplification technique for targeting specific DNA sequences. CPT utilizes a chimeric DNA-RNA-DNA probe that is cleaved by the enzyme ribonuclease (RNase H). In this study, using CPT, we aimed to detect the CYP2C19 gene polymorphism from noninvasive samples to determine extensive metabolizers (EMs) and PMs of CYP2C19.

Methods

DNA samples were extracted from hair, buccal mucosa, and blood cells. Primers and cycling probes were designed specifically for region G636A for exon 4 and G681A for exon 5, reported to be gene polymorphisms of CYP2C19.

Results

DNA extracted from hair follicle cells and buccal epithelial cells was the same as that collected from invasive blood sampling. The genotype of CYP2C19 was successfully identified as either EM or PM in 71 samples, producing identical results to those for the TaqMan method, except in three samples.

Conclusions

We successfully detected the two gene polymorphisms of CYP2C19 from noninvasive samples using a simple DNA extraction method and CPT.

Why Candida sepsis should matter to ICU physicians

The incidence of candidemia and invasive Candida infections has increased substantially over the last 2 decades. These infections are associated with risk factors that characterize intensive care unit patients. Candidemia and invasive Candida are highly morbid and associated with significantly increased mortality. Outcomes in the intensive care setting depend on physician awareness and rapid intervention. The epidemiology of the disease, its diagnostic challenges, and management strategies, including prophylactic, preemptive, and definitive therapeutic approaches, are presented herein.

Similarity in recombination rate and linkage disequilibrium at CYP2C and CYP2D cytochrome P450 gene regions among Europeans indicates signs of selection and no advantage of using tagSNPs in population isolates

OBJECTIVE

Linkage disequilibrium (LD) and recombination rate variations are known to vary considerably between human genome regions and populations mostly because of the combined effects of mutation, recombination, and demographic history. Thus, the pattern of LD is a key issue to disentangle variants associated with complex traits. Here, we aim to describe the haplotype structure and LD variation at the pharmacogenetically relevant cytochrome P450 CYP2C and CYP2D gene regions among European populations.

METHODS

To assess the haplotype structure, LD pattern, and recombination rate variations in the clinically significant CYP2C and CYP2D regions, we genotyped 143 single-nucleotide polymorphisms (SNPs) across these two genome regions in a diverse set of 11 European population samples and one sub-Saharan African sample.

RESULTS

Our results showed extended patterns of LD and in general a low rate of recombination at these loci, and a low degree of allele differentiation for the two cytochrome P450 regions among Europeans, with the exception of the Sami and the Finns as European outliers. The Sami sample showed reduced haplotype diversity and higher LD for the two cytochrome P450 regions than the other Europeans, a feature that is proposed to enhance the LD mapping of underlying common complex traits. However, recombination hotspots and LD blocks at these two regions showed highly consistent structures across Europeans including Finns and Sami. Moreover, we showed that the CEPH sample has significantly higher tag transferability among Europeans and a more efficient tagging of both the rare CYP2C9 and the common CYP2C19 functional variants than the Sami. Our data set included CYP2C9*3 (rs1057910) and CYP2C19*2 (rs4244285) enzyme activity-altering variants associated in a recent genome-wide study with acenocoumarol-induced and warfarin-induced anticoagulation or to the antiplatelet effect of clopidogrel, respectively. Including these known activity-altering variants, we showed the haplotype variation and high derived allele frequencies of novel recently identified acenocoumarol genome-wide associated SNPs at CYP2C9 (rs4086116) and CYP2C18 (rs12772169, rs1998591, rs2104543, rs1042194) loci in a comprehensive set of 11 European populations. Furthermore, a significant frequency difference of a CYP2C19*2 gene mutation causing variable drug reactions was observed among Europeans.

CONCLUSION

The CEPH sample representing the general European population as such in the HapMap project seems to be the optimal population sample for the LD mapping of common complex traits among Europeans. Nevertheless, it is still argued that the unique pattern of LD in the Sami may offer an advantage for further association mapping, especially if multiple rare variants play a role in disease etiology. However, besides the activity-altering CYP2C9*3 (rs1057910) and CYP2C19*2 (rs4244285) variants, the high derived allele frequencies of novel recently identified acenocoumarol genome-wide associated SNPs at CYP2C9 (rs4086116) and CYP2C18 (rs12772169, rs1998591, rs2104543, rs1042194) loci variants indicated that the CYP2C region may have been influenced by selection. Thus, this fine-scale haplotype map of the CYP2C and CYP2D regions may help to choose markers for further association mapping of complex pharmacogenetic traits at these loci.

Genotype-phenotype correlation of cytochrome P450 2C9 polymorphism in Indian National Capital Region

Identification of polymorphism of cytochrome P450 2C9 (CYP2C9) enzymes in different ethnic populations is important to understand the differences in clinical responses to drugs. This study determines the CYP2C9 genetic polymorphism in Indian National Capital Region and correlates the phenotype-genotype. Losartan (25 mg) was administered to 107 volunteers to assess CYP2C9 activity, and, on the basis of results, volunteers were categorized as rapid and poor metabolizers. Molecular typing of CYP2C9*1 (wild type), CYP2C9*2, and CYP2C9*3 (the most common variant) was carried out by single-base primer extension technology for 37 subjects, of which 9 were poor metabolizers, and 28 were rapid metabolizers. 14.28 % of the studied population was identified as poor metabolizer for the category of drugs metabolized by CYP2C9. Significant difference was observed between the mean ratio (drug/metabolite) of poor (11.38 ± 5.88) and rapid (1.18 ± 1.11) drug metabolizers. The study suggests that phenotyping of CYP2C9 is desirable before enrollment of subjects for clinical trials or for deciding drug dose regimen as 14.28 % of study population was found to be poor metabolizer for the category of drugs metabolized by CYP2C9. This study establishes phenotype-genotype correlation, and proposes to use genotyping or phenotyping to evaluate the status of drug metabolizing capacity of CYP2C9 as a primary screening procedure before enrolling subjects in clinical trials or in clinical practice.