CYP2C19 polymorphism affects single-dose pharmacokinetics of oral pantoprazole in healthy volunteers

Physiologically-based pharmacokinetic modeling of pantoprazole to evaluate the role of CYP2C19 genetic variation and obesity in the pediatric population

Pantoprazole is a proton pump inhibitor indicated for the treatment of gastroesophageal reflux disease, a condition that disproportionately affects children with obesity. Appropriately dosing pantoprazole in children with obesity requires understanding the body size metric that best guides dosing, but pharmacokinetic (PK) trials using traditional techniques are limited by the need for larger sample sizes and frequent blood sampling. Physiologically-based PK (PBPK) models are an attractive alternative that can account for physiologic-, genetic-, and drug-specific changes without the need for extensive clinical trial data. In this study, we explored the effect of obesity on pantoprazole PK and evaluated label-suggested dosing in this population. An adult PBPK model for pantoprazole was developed using data from the literature and accounting for genetic variation in CYP2C19. The adult PBPK model was scaled to children without obesity using age-associated changes in anatomical and physiological parameters. Lastly, the pediatric PBPK model was expanded to children with obesity. Three pantoprazole dosing strategies were evaluated: 1 mg/kg total body weight, 1.2 mg/kg lean body weight, and US Food and Drug Administration-recommended weight-tiered dosing. Simulated concentration-time profiles from our model were compared with data from a prospective cohort study (PAN01; NCT02186652). Weight-tiered dosing resulted in the most (>90%) children with pantoprazole exposures in the reference range, regardless of obesity status or CYP2C19 phenotype, confirming results from previously published population PK models. PBPK models may allow for the efficient study of physiologic and developmental effects of obesity on PK in special populations where clinical trial data may be limited.

Integrated models of population pharmacokinetics and exposure response to optimize dosage regimen for anaprazole sodium in duodenal ulcer

Anaprazole sodium enteric-coated tablet is a novel proton pump inhibitor which has been approved for the treatment of duodenal ulcer. The aim of this study is to provide reliable information for the design of an optimal dosage regimen. Population pharmacokinetics and exposure-response models were integrated to evaluate the pharmacokinetic parameters and covariates of Anaprazole and its metabolite M21-1, and subsequently provided dosage suggestions based on clinical trials and simulation data. A pharmacokinetic model incorporating two-compartment for the parent drug and one-compartment for the metabolite, with both first-order and zero-order mixed absorption was used to describe the pharmacokinetics of Anaprazole and M21-1. Age emerged as a significant covariate affecting the elimination rate constant of M21-1, with clearance decreasing as age advances. No correlation was observed between the pharmacokinetics of Anaprazole or M21-1 and the adverse reactions under the current dosages. BMI might be the influence factor of the mild gastrointestinal adverse reactions. Meanwhile, Anaprazole had a good healing rate (94.0 %) in duodenal ulcer patients and the exposure-response analysis indicated that the cured results were not influenced by the exposure parameters of parent drug or metabolite. In conclusion, the drug is safe when dosing between 20 and 100 mg once a day.

Association between proton pump inhibitors use and risk of asthma in Korea: A prevalent new-user cohort study

There have been conflicting mechanisms that proton pump inhibitors (PPIs) may promote or prevent asthma development. However, the evidence on the association of PPI use with the risk of asthma and its exposure-response relationship has been limited. We aim to identify the association between the use of PPIs and the incidence of asthma, compared with use of histamine 2 receptor antagonists (H2RAs). A nationwide, prevalent new-user cohort study was conducted using Korea's National Sample Cohort database. Patients were defined as PPI or H2RA users between 2003 and 2019. PPI users matched to H2RA users based on time-conditional propensity score. Cox proportional hazards model was used to estimate adjusted hazard ratios with 95% confidence intervals of incident asthma associated with PPI use by duration of use, cumulative dose, and average dose per duration. Among the 250,041 pairs, PPI users (51.3% male; mean [SD] age, 42.6 [16.5]; mean follow-up, 6.7 years) showed a higher incidence rate of asthma (7.94 events per 1000 person-year) compared to H2RA users (3.70 events per 1000 person-year) with adjusted hazard ratio of 2.15 (95% confidence interval = 2.08-2.21). The risk of asthma was significantly increased across all observed groups of duration of use, cumulative dose, and average dose per duration. This study suggested that PPI use is associated with an increased risk of developing asthma compared to H2RA use.

PBPK modeling to predict the pharmacokinetics of pantoprazole in different CYP2C19 genotypes

Pantoprazole is used to treat gastroesophageal reflux disease (GERD), maintain healing of erosive esophagitis (EE), and control symptoms related to Zollinger-Ellison syndrome (ZES). Pantoprazole is mainly metabolized by cytochrome P450 (CYP) 2C19, converting to 4'-demethyl pantoprazole. CYP2C19 is a genetically polymorphic enzyme, and the genetic polymorphism affects the pharmacokinetics and/or pharmacodynamics of pantoprazole. In this study, we aimed to establish the physiologically based pharmacokinetic (PBPK) model to predict the pharmacokinetics of pantoprazole in populations with various CYP2C19 metabolic activities. A comprehensive investigation of previous reports and drug databases was conducted to collect the clinical pharmacogenomic data, physicochemical data, and disposition properties of pantoprazole, and the collected data were used for model establishment. The model was evaluated by comparing the predicted plasma concentration-time profiles and/or pharmacokinetic parameters (AUC and Cmax) with the clinical observation results. The predicted plasma concentration-time profiles in different CYP2C19 phenotypes properly captured the observed profiles. All fold error values for AUC and Cmax were included in the two-fold range. Consequently, the minimal PBPK model for pantoprazole related to CYP2C19 genetic polymorphism was properly established and it can predict the pharmacokinetics of pantoprazole in different CYP2C19 phenotypes. The present model can broaden the insight into the individualized pharmacotherapy for pantoprazole.

CYP2C19 genotypes and osteoporotic fractures in long-term users of proton pump inhibitors: A hospital-based study

Proton pump inhibitors (PPIs) are commonly prescribed medications. The existing data suggest that individuals at a high risk of fractures have been exposed to high doses of PPIs for prolonged durations. CYP2C19 plays a pivotal role in metabolism of PPIs and thereby influences their pharmacokinetic profile. Hence, we hypothesize that CYP2C19 genotypes may be associated with fragility fracture among PPIs users due to PPI exposure. This study aimed to investigate the association between CYP2C19 genotypes, bone mineral density (BMD), and osteoporotic fracture in a hospital-based population. This retrospective cohort study enrolled patients who were prescribed long-term PPIs at Taichung Veterans General Hospital using data extracted from the Taiwan Precision Medicine Initiative between January 2010 and April 2021. Associations between CYP2C19 phenotypes, comorbidities, and fractures in PPI users were analyzed. We enrolled 1518 long-term PPI users; 571 (38%), 727 (48%), and 220 (14%) CYP2C19 normal metabolizers (NMs), intermediate metabolizers (IMs), and poor metabolizers (PMs), respectively. Among them, 49 (3.2%) patients developed fractures within the 1-year follow-up period; 20 (3.5%) fractures in NMs, 24 (3.3%) in IMs, and 5 (2.3%) in PMs, respectively. No significant difference was observed among CYP2C19 genotypes and fracture. Additionally, BMD measurements during the 1-year follow-up period were made available among 75 participants. No significant difference in BMD between CYP2C19 PMs and non-PMs was found. This real-world, hospital-based study concludes that CYP2C19 PMs/IMs are not associated with an increased risk for fractures or reduced BMD in individuals on long-term PPI therapy.

A Pharmacogenetics-Based Approach to Managing Gastroesophageal Reflux Disease: Current Perspectives and Future Steps

Proton pump inhibitors (PPIs) are commonly used medications to treat acid-related conditions, including gastro-esophageal reflux disease (GERD). Gastroenterology guidelines mention the importance of CYP2C19 in PPI metabolism and the influence of CYP2C19 genetic variations on variable responses to PPIs, but do not currently recommend the genotyping of CYP2C19 prior to prescribing PPIs. There are strong data to support the influence of CYP2C19 genetic variations on the pharmacokinetics of PPIs and clinical outcomes. Existing pharmacogenetic guideline recommendations for dose increases focus on H. pylori and erosive esophagitis indications, but PPIs are also the main therapy for treating GERD. Recent data suggest GERD patients being treated with a PPI may also benefit from genotype-guided dosing. We summarize the literature supporting this contention and highlight future directions for improved management of patients with GERD through precision medicine approaches.

The impact of CYP2C19 genotype on phenoconversion by concomitant medication

Introduction: Pharmacogenetics-informed drug prescribing is increasingly applied in clinical practice. Typically, drug metabolizing phenotypes are determined based on genetic test results, whereupon dosage or drugs are adjusted. Drug-drug-interactions (DDIs) caused by concomitant medication can however cause mismatches between predicted and observed phenotypes (phenoconversion). Here we investigated the impact of CYP2C19 genotype on the outcome of CYP2C19-dependent DDIs in human liver microsomes. Methods: Liver samples from 40 patients were included, and genotyped for CYP2C19*2, *3 and *17 variants. S-mephenytoin metabolism in microsomal fractions was used as proxy for CYP2C19 activity, and concordance between genotype-predicted and observed CYP2C19 phenotype was examined. Individual microsomes were subsequently co-exposed to fluvoxamine, voriconazole, omeprazole or pantoprazole to simulate DDIs. Results: Maximal CYP2C19 activity (V_max) in genotype-predicted intermediate metabolizers (IMs; *1/*2 or *2/*17), rapid metabolizers (RMs; *1/*17) and ultrarapid metabolizers (UMs; *17/*17) was not different from V_max of predicted normal metabolizers (NMs; *1/*1). Conversely, CYP2C19*2/*2 genotyped-donors exhibited V_max rates ∼9% of NMs, confirming the genotype-predicted poor metabolizer (PM) phenotype. Categorizing CYP2C19 activity, we found a 40% concordance between genetically-predicted CYP2C19 phenotypes and measured phenotypes, indicating substantial phenoconversion. Eight patients (20%) exhibited CYP2C19 IM/PM phenotypes that were not predicted by their CYP2C19 genotype, of which six could be linked to the presence of diabetes or liver disease. In subsequent DDI experiments, CYP2C19 activity was inhibited by omeprazole (-37% ± 8%), voriconazole (-59% ± 4%) and fluvoxamine (-85% ± 2%), but not by pantoprazole (-2 ± 4%). The strength of CYP2C19 inhibitors remained unaffected by CYP2C19 genotype, as similar percental declines in CYP2C19 activity and comparable metabolism-dependent inhibitory constants (K_inact/K_I) of omeprazole were observed between CYP2C19 genotypes. However, the consequences of CYP2C19 inhibitor-mediated phenoconversion were different between CYP2C19 genotypes. In example, voriconazole converted 50% of *1/*1 donors to a IM/PM phenotype, but only 14% of *1/*17 donors. Fluvoxamine converted all donors to phenotypic IMs/PMs, but *1/*17 (14%) were less likely to become PMs than *1/*1 (50%) or *1/*2 and *2/*17 (57%). Conclusion: This study suggests that the differential outcome of CYP2C19-mediated DDIs between genotypes are primarily dictated by basal CYP2C19 activity, that may in part be predicted by CYP2C19 genotype but likely also depends on disease-related factors.

Pharmacogenomics in allogeneic hematopoietic stem cell transplantation: Implications on supportive therapies and conditioning regimens

Allogeneic hematopoietic stem cell transplantation mortality has declined over the years, though prevention and management of treatment-related toxicities and post-transplant complications remains challenging. Applications of pharmacogenomic testing can potentially mitigate adverse drug outcomes due to interindividual variability in drug metabolism and response. This review summarizes clinical pharmacogenomic applications relevant to hematopoietic stem cell transplantation, including antifungals, immunosuppressants, and supportive care management, as well as emerging pharmacogenomic evidence with conditioning regimens.

Compounding of Liquid and Solid Dose Adjustable Formulations with Pantoprazole: Comparison of Stability, Applicability and Suitability

Pantoprazole is a model substance that requires dosage form adjustments to meet the needs of all patients. Pediatric pantoprazole formulations in Serbia are mostly compounded as capsules (divided powders), while in Western Europe liquid formulations are more common. The aim of this work was to examine and compare the characteristics of compounded liquid and solid dosage forms of pantoprazole. Three syrup bases were used: a sugar-free vehicle for oral solution (according to USP43-NF38), a vehicle with glucose and hydroxypropyl cellulose (according to the DAC/NRF2018) and a commercially available SyrSpend Alka base. Lactose monohydrate, microcrystalline cellulose and a commercially available capsule filler (excipient II, composition: pregelatinized corn starch, magnesium stearate, micronized silicon dioxide, micronized talc) were used as diluents in the capsule formulations. Pantoprazole concentration was determined by the usage of the HPLC method. Pharmaceutical technological procedures and microbiological stability measurements were performed according to the recommendations of the EP10. Although dose appropriate compounding with pantoprazole is suitable using both liquid vehicles as well as solid formulations, chemical stability is enhanced in solid formulation. Nevertheless, according to our results, if liquid formulation is a pH adjusted syrup, it could be safely kept in a refrigerator for up to 4 weeks. Additionally, liquid formulations could be readily applied, while solid formulation should be mixed with appropriate vehicles with higher pH values.

Association between Migraines and Prior Proton Pump Inhibitor Use: A Nested Case-Control Study Using a National Health Screening Cohort

The effect of proton pump inhibitor (PPI) use on migraine risk remains controversial. We explored the odds of migraines in relation to prior PPI use and treatment duration. Data from the Korean National Health Insurance Service-Health Screening Cohort (2002−2015) were analyzed in this nested case-control study involving 28,159 participants with incident migraines and 112,636 controls (1:4 matched by sex, age, income, and residential region). The baseline covariates were balanced by performing propensity score overlap weighting-based adjustments, and the effect of prior PPI use (past vs. current) and treatment duration (<30 and 30−365 days vs. ≥365 days) on incident migraines was evaluated using logistic regression. In past and current PPI users, prior PPI use raised the likelihood of migraines (adjusted odds ratio [95% confidence interval]: 2.56 [2.36−2.79] and 4.66 [4.29−5.06], respectively). Participants who used PPI for <30, 30−365, or ≥365 days exhibited high odds of migraines (2.49 [2.29−2.72], 4.41 [4.05−4.79], and 4.14 [3.77−4.54], respectively). Incident migraines with or without aura also increased independently of PPI use history or duration. In summary, prior PPI use, irrespective of the elapsed time since use and the duration of use, is possibly associated with incident migraines with or without aura.

Pharmacogenetics of Praziquantel Metabolism: Evaluating the Cytochrome P450 Genes of Zimbabwean Patients During a Schistosomiasis Treatment

Schistosomiasis is a parasitic disease infecting over 236 million people annually, with the majority affected residing on the African continent. Control of this disease is reliant on the drug praziquantel (PZQ), with treatment success dependent on an individual reaching PZQ concentrations lethal to schistosomes. Despite the complete reliance on PZQ to treat schistosomiasis in Africa, the characterization of the pharmacogenetics associated with PZQ metabolism in African populations has been sparse. We aimed to characterize genetic variation in the drug-metabolising cytochrome P450 enzymes (CYPs) and determine the association between each variant and the efficacy of PZQ treatment in Zimbabwean patients exposed to Schistosoma haematobium infection. Genomic DNA from blood samples of 114 case-control Zimbabweans infected with schistosomes were sequenced using the CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP3A4, and CYP3A5 genes as targets. Bioinformatic tools were used to identify and predict functional effects of detected single nucleotide polymorphisms (SNPs). A random forest (RF) model was then used to assess SNPs most predictive of PZQ efficacy, with a misclassification rate of 29%. SNPs were detected across all six genes, with 70 SNPs identified and multiple functional changes to the CYP enzymes predicted. Only four SNPs were significantly associated with PZQ efficacy using χ² tests, with rs951840747 (OR: 3.61, p = 0.01) in the CYP1A2 gene having the highest odds of an individual possessing this SNP clearing infection, and rs6976017 (OR: 2.19, p = 0.045) of CYP3A5 determined to be the most predictive of PZQ efficacy via the RF. Only the rs28371702 (CC) genotype (OR: 2.36, p = 0.024) of CYP2D6 was significantly associated with an unsuccessful PZQ treatment. This study adds to the genomic characterization of the diverse populations in Africa and identifies variants relevant to other pharmacogenetic studies crucial for the development and usage of drugs in these populations.

Population pharmacogenomics: an update on ethnogeographic differences and opportunities for precision public health

Both safety and efficacy of medical treatment can vary depending on the ethnogeographic background of the patient. One of the reasons underlying this variability is differences in pharmacogenetic polymorphisms in genes involved in drug disposition, as well as in drug targets. Knowledge and appreciation of these differences is thus essential to optimize population-stratified care. Here, we provide an extensive updated analysis of population pharmacogenomics in ten pharmacokinetic genes (CYP2D6, CYP2C19, DPYD, TPMT, NUDT15 and SLC22A1), drug targets (CFTR) and genes involved in drug hypersensitivity (HLA-A, HLA-B) or drug-induced acute hemolytic anemia (G6PD). Combined, polymorphisms in the analyzed genes affect the pharmacology, efficacy or safety of 141 different drugs and therapeutic regimens. The data reveal pronounced differences in the genetic landscape, complexity and variant frequencies between ethnogeographic groups. Reduced function alleles of CYP2D6, SLC22A1 and CFTR were most prevalent in individuals of European descent, whereas DPYD and TPMT deficiencies were most common in Sub-Saharan Africa. Oceanian populations showed the highest frequencies of CYP2C19 loss-of-function alleles while their inferred CYP2D6 activity was among the highest worldwide. Frequencies of HLA-B*15:02 and HLA-B*58:01 were highest across Asia, which has important implications for the risk of severe cutaneous adverse reactions upon treatment with carbamazepine and allopurinol. G6PD deficiencies were most frequent in Africa, the Middle East and Southeast Asia with pronounced differences in variant composition. These variability data provide an important resource to inform cost-effectiveness modeling and guide population-specific genotyping strategies with the goal of optimizing the implementation of precision public health.

Targeted temperature management after cardiac arrest is associated with reduced metabolism of pantoprazole - A probe drug of CYP2C19 metabolism

OBJECTIVE

Targeted temperature management (TTM) is part of standard post-resuscitation care. TTM may downregulate cytochrome enzyme activity and thus impact drug metabolism. This study compared the pharmacokinetics (PK) of pantoprazole, a probe drug of CYP2C19-dependent metabolism, at different stages of TTM following cardiac arrest.

METHODS

This prospective controlled study was performed at the Medical University of Vienna and enrolled 16 patients following cardiac arrest. The patients completed up to three study periods (each lasting 24 h) in which plasma concentrations of pantoprazole were quantified: (P1) hypothermia (33 °C) after admission, (P2) normothermia after rewarming (36 °C, intensive care), and (P3) normothermia during recovery (normal ward, control group). PK was analysed using non-compartmental analysis and nonlinear mixed-effects modelling.

RESULTS

16 patients completed periods P1 and P2; ten completed P3. The median half-life of pantoprazole was 2.4 h (quartiles: 1.8-4.8 h) in P1, 2.8 h (2.1-6.8 h, p = 0.046 vs. P1, p = 0.005 vs. P3) in P2 and 1.2 h (0.9 - 2.3 h, p = 0.007 vs. P1) in P3. A two-compartment model described the PK data best. Typical values for clearance were estimated separately for each study period, indicating 40% and 29% reductions during P1 and P2, respectively, compared to P3. The central volume of distribution was estimated separately for P2, indicating a 64% increase compared to P1 and P3.

CONCLUSION

CYP2C19-dependent drug metabolism is downregulated during TTM following cardiac arrest. These results may influence drug choice and dosing of similarly metabolized drugs and may be helpful for designing studies in similar clinical situations.

Anti-interleukin-6 antibody clazakizumab in late antibody-mediated kidney transplant rejection: effect on cytochrome P450 drug metabolism

Targeting interleukin-6 (IL-6) is a promising strategy to counteract antibody-mediated rejection (ABMR). In inflammatory states, IL-6 antagonism was shown to modulate cytochrome P450 (CYP), but its impact on drug metabolism in ABMR treatment was not addressed so far. We report a sub-study of a phase 2 trial of anti-IL-6 antibody clazakizumab in late ABMR (ClinicalTrials.gov, NCT03444103). Twenty kidney transplant recipients were randomized to clazakizumab versus placebo (4-weekly doses; 12 weeks), followed by a 9-month extension where all recipients received clazakizumab. To study CYP2C19/CYP3A4 metabolism, we administered pantoprazole (20 mg intravenously) at prespecified time points. Dose-adjusted C₀ levels (C₀ /D ratio) of tacrolimus (n = 13) and cyclosporin A (CyA, n = 6) were monitored at 4-weekly intervals. IL-6 and C-reactive protein were not elevated at baseline, the latter was then suppressed to undetectable levels under clazakizumab. IL-6 blockade had no clinically meaningful impact on pantoprazole pharmacokinetics (area under the curve; baseline versus week 52: 3.16 [2.21-7.84] versus 4.22 [1.99-8.18] μg/ml*h, P = 0.36) or calcineurin inhibitor C₀ /D ratios (tacrolimus: 1.49 [1.17-3.20] versus 1.37 [0.98-2.42] ng/ml/mg, P = 0.21; CyA: 0.69 [0.57-0.85] versus 1.08 [0.52-1.38] ng/ml/mg, P = 0.47). We conclude that IL-6 blockade in ABMR - in absence of systemic inflammation - may have no meaningful effect on CYP metabolism.

Enriching Medication Review with a Pharmacogenetic Profile - A Case of Tamoxifen Adverse Drug Reactions

Pharmacogenotyping is applied to determine the hereditable component of a patient's susceptibility to experience therapy failure and/or adverse drug reactions (ADRs). We present the case of a female patient diagnosed with breast cancer and treated with tamoxifen as recurrence therapy who experienced various ADRs. Pharmacogenotyping revealed variants in the cytochrome P450 (CYP) enzymes CYP2D6, CYP2C9, and CYP2C19. The observed genotype was associated with a risk for lower tamoxifen efficacy. Aside from the tamoxifen therapy, the comedication was reviewed for the influence of the patient’s pharmacogenetic profile. As a result of this pharmacist-led medication review with pharmacogenetic analyses, concrete genotype-driven recommendations for the treating gynecologist were compiled. This case revealed the added value of a large pharmacogenetic panel and the complexity of integrating a pharmacogenetic profile into a recommendation.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2C19 and Proton Pump Inhibitor Dosing

Proton pump inhibitors (PPIs) are widely used for acid suppression in the treatment and prevention of many conditions, including gastroesophageal reflux disease, gastric and duodenal ulcers, erosive esophagitis, Helicobacter pylori infection, and pathological hypersecretory conditions. Most PPIs are metabolized primarily by cytochrome P450 2C19 (CYP2C19) into inactive metabolites, and CYP2C19 genotype has been linked to PPI exposure, efficacy, and adverse effects. We summarize the evidence from the literature and provide therapeutic recommendations for PPI prescribing based on CYP2C19 genotype (updates at www.cpicpgx.org). The potential benefits of using CYP2C19 genotype data to guide PPI therapy include (i) identifying patients with genotypes predictive of lower plasma exposure and prescribing them a higher dose that will increase the likelihood of efficacy, and (ii) identifying patients on chronic therapy with genotypes predictive of higher plasma exposure and prescribing them a decreased dose to minimize the risk of toxicity that is associated with long-term PPI use, particularly at higher plasma concentrations.

Role of Genetic Polymorphisms of Cytochrome P450 2C19 in Pantoprazole Metabolism and Pantoprazole-based Helicobacter pylori Eradication Regimens

BACKGROUND

Cytochrome P450 (CYP450) enzymes play an important role in the metabolism of 70-80% of the currently used medications, including proton pump inhibitors. There are some data analyzing the impact of gene polymorphisms of CYP450 enzymes on most widely used PPIs, such as omeprazole, however, the data on pantoprazole are highly lacking.

OBJECTIVE

To summarize the most recent publications and studies on the role of polymorphisms of the genes encoding CYP450 enzyme 2C19 in the metabolism of pantoprazole and pantoprazole based Helicobacter pylori eradication regimens.

METHODS

We performed a non-systematic search of the available literature on the selected topic.

RESULTS AND CONCLUSION

The data on cytochrome P450 gene polymorphisms and their role in pantoprazole metabolism and pantoprazole based Helicobacter pylori eradication remain conflicting. Individual differences in pantoprazole metabolism might be partly related to genetic polymorphisms of CYP450 enzymes. Most of the studies support the observation that cytochrome 2C19 polymorphisms have an impact on the pharmacokinetics of pantoprazole and its therapeutic effects: poor metabolizers of PPIs are more likely to have a better response to pantoprazole therapy and achieve better H. pylori eradication rates compared to rapid metabolizers. The determination of alleles that are associated with decreased (e.g., *2, *3 alleles) or increased (e.g., *17 allele) cytochrome 2C19 enzyme activity might be used as predictive factors for the potential of acid suppression and the success of Helicobacter pylori eradication. Overall, currently available data do not provide robust evidence, therefore, the application of genetic polymorphisms of cytochrome enzymes in clinical practice still cannot be recommended as routine practice for personalized pantoprazole prescription strategies.

CYP2C19 Phenotype and Risk of Proton Pump Inhibitor-Associated Infections

OBJECTIVES

Proton pump inhibitors (PPIs) are often used in pediatrics to treat common gastrointestinal disorders, and there are growing concerns for infectious adverse events. Because CYP2C19 inactivates PPIs, genetic variants that increase CYP2C19 function may decrease PPI exposure and infections. We tested the hypothesis that CYP2C19 metabolizer phenotypes are associated with infection event rates in children exposed to PPIs.

METHODS

This retrospective biorepository cohort study included individuals aged 0 to 36 months at the time of PPI exposure. Respiratory tract and gastrointestinal tract infection events were identified by using International Classification of Diseases codes in the year after the first PPI mention. Variants defining CYP2C19 *2, *3, *4, *8, *9, and *17 were genotyped, and all individuals were classified as CYP2C19 poor or intermediate, normal metabolizers (NMs), or rapid or ultrarapid metabolizers (RM/UMs). Infection rates were compared by using univariate and multivariate analyses.

RESULTS

In all, 670 individuals were included (median age 7 months; 44% girls). CYP2C19 NMs (n = 267; 40%) had a higher infection rate than RM/UMs (n = 220; 33%; median 2 vs 1 infections per person per year; P = .03). There was no difference between poor or intermediate (n = 183; 27%) and NMs. In multivariable analysis of NMs and RM/UMs adjusting for age, sex, PPI dose, and comorbidities, CYP2C19 metabolizer status remained a significant risk factor for infection events (odds ratio 0.70 [95% confidence interval 0.50-0.97] for RM/UMs versus NMs).

CONCLUSIONS

PPI therapy is associated with higher infection rates in children with normal CYP2C19 function than in those with increased CYP2C19 function, highlighting this adverse effect of PPI therapy and the relevance of CYP2C19 genotypes to PPI therapeutic decision-making.

Factors Influencing the Safety and Efficiency of Antifungal Prophylaxis with Posaconazole in Children with Hematological Diseases: From Genetics to Polypharmacotherapy

The aim of this study was to determine the impact of ABCB1 polymorphism, BMI, age and drug co-administration on safety and efficiency of posaconazole (PCZ) oral suspension treatment in children with hematological diseases. Seventy children were included in the study. ABCB1 polymorphism in fifty-eight children was determined using a PCR–RFLP method. A protocol with data on the health condition, treatment and adverse events (AE), as well as a survey on treatment tolerance for the legal guardians was evaluated. Liver function tests were observed for the first 20 days, and AE during the complete medication period. For statistical analysis a χ² test with Yates’s correction, a Pearson’s or Spearman’s correlation test was performed (p < 0.05). Genetic testing showed 24% CC, 46% CT and 30% of TT variants. PCZ prophylaxis failed in twenty cases, where change in prophylactic treatment was needed. Fifty-two children suffered from at least one mild to moderate adverse event. Sixty-five legal guardians completed the survey, most of them reported the treatment to be well tolerated. ABCB1 polymorphism had no impact on AE occurrence and posaconazole prophylaxis efficiency. Age influenced the number of gastrointestinal (p = 0.02), visual (p = 0.05), neurological (p = 0.01), dermatological (p = 0.002) and flu-like (p = 0.02) complications. AST (p = 0.03) and LDH (p = 0.008) activity presented age dependency. The concomitant use of proton pump inhibitors (PPI) had impact on liver health parameters elevation (p = 0.009) and circulatory system complications (p = 0.008). High incidence of mild to moderate AE, and other factors influencing PCZ pharmacokinetics (PPI co-administration, obesity), suggest a need for careful pediatric onco-hematology patient evaluation.

Effects of the Proton Pump Inhibitors Omeprazole and Pantoprazole on the Cytochrome P450-Mediated Metabolism of Venlafaxine

BACKGROUND AND OBJECTIVE: An increasing trend in prescribing proton pump inhibitors (PPIs) inevitably increases the risk of unwanted drug-drug interactions (DDIs). The aim of this study was to uncover pharmacokinetic interactions between two PPIs-omeprazole and pantoprazole-and venlafaxine.

METHODS

A therapeutic drug monitoring database contained plasma concentrations of venlafaxine and its active metabolite O-desmethylvenlafaxine. We considered three groups: a group of patients who received venlafaxine without confounding medications (non-PPI group, n = 906); a group of patients who were comedicated with omeprazole (n = 40); and a group of patients comedicated with pantoprazole (n = 40). Plasma concentrations of venlafaxine, O-desmethylvenlafaxine and active moiety (venlafaxine + O-desmethylvenlafaxine), as well as dose-adjusted plasma concentrations, were compared using non-parametrical tests.

RESULTS

Daily doses of venlafaxine did not differ between groups (p = 0.949). The Mann-Whitney U test showed significantly higher plasma concentrations of active moiety, as well as venlafaxine and O-desmethylvenlafaxine, in both PPI groups [p = 0.023, p = 0.011, p = 0.026, +29% active moiety, +27% venlafaxine, +36% O-desmethylvenlafaxine (pantoprazole); p = 0.003, p = 0.039 and p < 0.001, +36% active moiety, +27% venlafaxine, +55% O-desmethylvenlafaxine (omeprazole)]. Significantly higher concentration-by-dose (C/D) values for venlafaxine and active moiety were detected in the pantoprazole group (p = 0.013, p = 0.006, respectively), while in the omeprazole group, C/D ratios for all three parameters-venlafaxine, O-desmethylvenlafaxine and active moiety-were significantly higher (p = 0.021, p < 0.001 and p < 0.001, respectively).

CONCLUSIONS

Significantly higher plasma concentrations for all parameters (venlafaxine, O-desmethylvenlafaxine, active moiety) suggest clinically relevant inhibitory effects of both PPIs, most likely on the cytochrome P450 (CYP) 2C19-mediated metabolism of venlafaxine. The findings might be the result of different degrees of CYP2C19 involvement, therefore the inhibition of CYP2C19 by both PPIs may lead to an increased metabolism via CYP2D6 to O-desmethylvenlafaxine.

Assessing CYP2C19 Ontogeny in Neonates and Infants Using Physiologically Based Pharmacokinetic Models: Impact of Enzyme Maturation Versus Inhibition

The objective of this study was to develop pediatric physiologically based pharmacokinetic (PBPK) models for pantoprazole and esomeprazole. Pediatric PBPK models were developed by Simcyp version 15 by incorporating cytochrome P450 (CYP)2C19 maturation and auto-inhibition. The predicted-to-observed pantoprazole clearance (CL) ratio ranged from 0.96-1.35 in children 1-17 years of age and 0.43-0.70 in term infants. The predicted-to-observed esomeprazole CL ratio ranged from 1.08-1.50 for children 6-17 years of age, and 0.15-0.33 for infants. The prediction was markedly improved by assuming no auto-inhibition of esomeprazole in infants in the PBPK model. Our results suggested that the CYP2C19 auto-inhibition model was appropriate for esomeprazole in adults and older children but could not be directly extended to infants. A better understanding of the complex interplay of enzyme maturation, inhibition, and compensatory mechanisms for CYP2C19 is necessary for PBPK modeling in infants.

Population PK-PD Model of Pegylated Interferon Alfa-2a in Healthy Korean Men

Pegylated interferon alfa-2a (PEG-IFN alfa-2a), which was developed to overcome the disadvantages of conventional formulations, is widely prescribed for hepatitis B or C virus infection. It is characterized by pharmacokinetic (PK) and pharmacodynamic (PD) properties much different from those of conventional forms. The present study developed a population PK-PD model of subcutaneous PEG-IFN alfa-2a in a Korean population. For PK, IFN alfa-2a concentrations were described by a 1-compartment model with first-order absorption, preceded by skin-to-depot first-order input. For PD, serum 2'-5' oligoadenylsynthetase activity was described by an effect compartment model incorporating a tolerance compartment. The baseline serum 2'-5' oligoadenylsynthetase level was found to have an inverse relationship with sensitivity to tolerance, leading to high tolerance at low baseline. The model revealed that subjects with low baselines experienced time delay, while those with high baselines showed tolerance in their concentration-effect relationships. The developed models matched well with data and simulation results, and the model showed that the optimal dose decreases with the baseline, with no dose effective for a baseline >250 pmol/dL. Our results can serve as a basis for improving dosing regimens of PEG-IFN alfa-2a in adult patients with chronic hepatitis B or C infection.

Proton pump inhibitors: from CYP2C19 pharmacogenetics to precision medicine

Introduction: Proton Pump inhibitors (PPIs) are commonly used for a variety of acid related disorders. Despite the overall effectiveness and safety profile of PPIs, some patients do not respond adequately or develop treatment related adverse events. This variable response among patients is in part due to genotype variability of CYP2C19, the gene encoding the CYP450 (CYP2C19) isoenzyme responsible for PPIs metabolism.

Areas covered: This article provides an overview of the pharmacokinetics and mechanism of action of the currently available PPIs, including the magnitude of CYPC19 contribution to their metabolism. Additionally, the role of CYP2C19 genetic variability in the therapeutic effectiveness or outcomes of PPI therapy is highlighted in details, to provide supporting evidence for the potential value of CYP2C19 genotype-guided approaches to PPI drug therapy.

Expert opinion: There is a large body of evidence describing the impact of CYP2C19 variability on PPIs and its potential role in individualizing PPI therapy, yet, CYP2C19 pharmacogenetics has not been widely implemented into clinical practice. More data are needed but CYP2C19 genotype-guided dosing of PPIs is likely to become increasingly common and is expected to improve clinical outcomes, and minimize side effects related to PPIs.

Prevalence of the CYP2C19*2 (681 G>A), *3 (636 G>A) and *17 (‑806 C>T) alleles among an Iranian population of different ethnicities

Polymorphisms in the cytochrome P (CYP) 450 family may cause adverse drug responses in individuals. Cytochrome P450 2C19 (CYP2C19) is a member of the CYP family, where the presence of the 681 G>A, 636 G>A and 806 C>T polymorphisms result in the CYP2C19*2, CYP2C19*3 and CYP2C19*17 alleles, respectively. In the current study, the frequency of the CYP2C19*2, CYP2C19*3 and CYP2C19*17 alleles in an Iranian population cohort of different ethnicities were examined and then compared with previously published frequencies within other populations. Allelic and genotypic frequencies of the CYP2C19 alleles (*2, *3 and *17) were detected using polymerase chain reaction (PCR)-restriction fragment length polymorphism analysis, PCR-single-strand conformation polymorphism analysis and DNA sequencing from blood samples of 1,229 unrelated healthy individuals from different ethnicities within the Iranian population. The CYP2C19 allele frequencies among the Iranian population were 21.4, 1.7, and 27.1% for the CYP2C19*2, CYP2C19*3 and CYP2C19*17 alleles, respectively. The frequency of the homozygous A/A variant of the CYP2C19*2 allele was significantly high and low in the Lur (P<0.001) and Caspian (P<0.001) ethnicities, respectively. However, the frequency of the homozygous A/A variant of the CYP2C19*3 allele was not detected in the Iranian cohort in the current study. The frequency of the heterozygous G/A variant of the CYP2C19*3 allele had the significantly highest and lowest frequency in the Fars (P<0.001) and Lur (P<0.001) groups, respectively. The allele frequency of the homozygous T/T variant of the CYP2C19*17 allele was significantly high in the Caspian (P<0.001) and low in the Kurd (P<0.05) groups. The frequency of the CYP2C19 alleles involved in drug metabolism, may improve the clinical understanding of the ethnic differences in drug responses, resulting in the advancement of the personalized medicine among the different ethnicities within the Iranian population.

Association between CYP2C19 extensive metabolizer phenotype and childhood anti-reflux surgery following failed proton pump inhibitor medication treatment

When pediatric gastroesophageal reflux disease (GERD) that is refractory to proton pump inhibitor (PPI) medication treatment is identified in clinical practice and anti-reflux surgery (ARS) is being considered, genetic factors related to PPI metabolism by the CYP2C19 enzyme are currently not part of the clinical decision-making process. Our objective was to test the hypothesis that the distribution of the extensive metabolizer (EM) phenotypes among children undergoing ARS after failing PPI therapy would differ compared to controls (children with no history of ARS). We conducted a case-control study between children across the Nemours Health System from 2000 to 2014 who received ARS after failing PPI therapy and a control group comprised of healthy children. Our results demonstrated 2.9% of ARSs vs 20.8% of controls were poor metabolizers (PMs), 55.9% of ARSs vs 49.0% of controls were normal metabolizers (NMs), and 41.2% of ARSs vs 30.2% of controls were EMs; p = 0.035. Next, we performed a multiple-regression model to account for race as a potential confounding variable and the EM group was significantly associated with ARS compared to controls (OR 9.78, CI 1.25-76.55, p < 0.03).

CONCLUSION

Among children with medically refractory GERD despite PPI therapy, carriage of CYP2C19*17 allele corresponding to the EM phenotype was associated with ARS. Prospective comparative personalized medicine effectiveness studies are needed to determine if CYP2C19 genotype-guided dosing improves response to PPI therapy without a corresponding increase in adverse effects in children. What is known: • Anti-reflux surgery (ARS) is one of the most common surgical procedures performed in children for the indication of refractory gastroesophageal reflux disease (GERD). What is new: • Individualizing PPI medication dosing based on CYP2C19 diplotype may avoid GERD treatment failures and reduce the need for anti-reflux surgery (ARS).

Clopidogrel in Critically Ill Patients

Only limited data are available regarding the treatment of critically ill patients with clopidogrel. This trial investigated the effects and the drug concentrations of the cytochrome P450 (CYP450) activated prodrug clopidogrel (n = 43) and the half‐life of the similarly metabolized pantoprazole (n = 16) in critically ill patients. ADP‐induced aggregometry in whole blood classified 74% (95% confidence intervals 59–87%) of critically ill patients as poor responders (n = 43), and 65% (49–79%) responded poorly according to the vasodilator‐stimulated phosphoprotein phosphorylation (VASP‐P) assay. Although the plasma levels of clopidogrel active metabolite normally exceed the inactive prodrug ∼30‐fold, the parent drug levels even exceeded those of the metabolite 2‐fold in critically ill patients. The half‐life of pantoprazole was several‐fold longer in these patients compared with reference populations. The inverse ratio of prodrug/active metabolite indicates insufficient metabolization of clopidogrel, which is independently confirmed by the ∼5‐fold increase in half‐life of pantoprazole. Thus, high‐risk patients may benefit from treatment with alternative platelet inhibitors.

Effect of cytochrome P450 2C19*17 allelic variant on cardiovascular and cerebrovascular outcomes in clopidogrel-treated patients: A systematic review and meta-analysis

Background:

We aimed to evaluate the associations of gain-of-function allele of CYP2C19*17 and risk of clinical events in clopidogrel-treated patients with cardiovascular and cerebrovascular diseases (CCVDs).

Materials and Methods:

Literature search was conducted in PubMed, EMBASE, and Cochrane Library. Odds ratio (OR) combined with 95% confidence interval (CI) was the pooled statistics. Subgroup analysis was performed by disease type, bleeding events, and race.

Results:

Thirteen eligible studies involving 14,239 patients with CYP2C19*17 carriers or noncarriers were included in the meta-analysis. CYP2C19*17 was significantly related to decreased risk of major adverse cardiovascular and cerebrovascular events (MACCEs) in patients with coronary artery disease (CAD) (OR = 0.76, 95% CI: 0.60–0.98, P = 0.03), however, irrelevant with stent thrombosis in neither CAD nor ischemic heart disease patients. CYP2C19*17 was also significantly linked to decreased risk of high platelet reactivity (HPR) in CCVD patients (OR = 0.61, 95% CI: 0.43–0.88, P = 0.008). Meanwhile, CYP2C19*17 was significantly associated with bleeding risk in CCVD patients (OR = 1.89, 95% CI: 1.09–3.25, P = 0.02) but not related to major bleeding risk (OR = 1.35, 95% CI: 0.87–2.08, P = 0.18). Several outcomes in Caucasian subgroup were reverse to the overall results, such as bleeding events and HPR, which lacked significance.

Conclusion:

CYP2C19*17 had a significant effect on the reduced risks of MACCE and HPR as well as increased bleeding risk, but not on the risks of stent thrombosis and major bleeding in clopidogrel-treated CCVD patients. Outcomes might be different in different races.

Impact of Gastric H+/K+-ATPase rs2733743 on the Intragastric pH-Values of Dexlansoprazole Injection in Chinese Subjects

Background: Not all patients with acid-related disorders receiving proton pump inhibitor (PP) treatment get adequate gastric pH control. The genetic variation of receptors, metabolic enzymes, and transporters are known to cause failures of therapies. We have conducted a study to evaluate the influence of gastric H⁺/K⁺-ATPase, CYP2C19, and ABCB1 polymorphisms on the pharmacokinetic and pharmacodynamic profiles of dexlansoprazole injection in healthy Chinese subjects.

Methods: A total of 51 subjects were enrolled for pharmacokinetic and pharmacodynamic study after a single intravenous administration of 20 or 30 mg dexlansoprazole. Plasma concentrations were determined using a chiral liquid chromatography-mass spectrometry method. The intragastric pH and baseline-adjusted intragastric pH parameters were introduced to evaluate the pharmacodynamic characters. Genotyping was performed by polymerase chain reaction.

Results: The pharmacokinetic parameters were significantly influenced by CYP2C19 phenotypes, and gastric acid secretion inhibition were affected by both gastric H⁺/K⁺-ATPase and CYP2C19 polymorphisms. Gastric H⁺/K⁺-ATPase genotypes had greater effects than CYP2C19 genotypes on the suppression of gastric acid secretion.

Conclusion: Gastric H⁺/K⁺-ATPase polymorphism may be one of the main reasons that cause insufficient gastric acid inhibition.

Association Between CYP2C19*17 Alleles and pH Probe Testing Outcomes in Children With Symptomatic Gastroesophageal Reflux

Esophageal pH monitoring remains a primary diagnostic tool for detecting gastroesophageal reflux disease (GERD). GERD that is refractory to proton pump inhibitor (PPI) medications may be related to CYP2C19 variants. Current PPI dosing practices in children do not take into account CYP2C19 allelic variants, which may lead to underdosing and subsequently to a misperception of PPI therapy failure. We hypothesized that pH probe acid exposure outcomes associate with CYP2C19*17 alleles among children with clinical concern for GERD. We identified a retrospective cohort of 74 children (age range 0.71-17.1 years, mean 8.5, SD 4.6) with stored endoscopic tissue samples and who had also undergone esophageal pH testing while on PPI therapy. These individuals were genotyped for common CYP2C19 alleles and were dichotomized to either CYP2C19*17 allelic carriers without corresponding loss of function alleles as cases vs controls. Associations between pH probe acid exposure outcomes and CYP2C19*17 alleles were investigated. Compared to controls, children who carry CYP2C19*17 alleles without corresponding loss-of-function alleles demonstrated statistically significant longer times with pH < 4 (76.46 vs 33.47 minutes, P = .03); and higher percent of time with pH < 4.0 (5.71 vs 2.67 minutes, P = .04). These findings remained statistically significant using multiple-regression modeling with test duration, PPI dose, and race as confounding variables. PPI therapy in children with *17 alleles may be better optimized with CYP2C19 genotype-guided dosing prior to pH probe testing.

Effects of Genetic Polymorphisms of Cytochrome P450 Enzymes and MDR1 Transporter on Pantoprazole Metabolism and Helicobacter pylori Eradication

Pantoprazole is a proton pump inhibitor that is commonly used in the treatment of peptic ulcer disease (PUD) and metabolized by cytochrome P450 (CYP) enzymes CYP2C19 and CYP3A4. Pantoprazole is a substrate for multi-drug resistance protein 1 (MDR1). Single nucleotide polymorphisms (SNPs) in CYP2C19, CYP3A4 and MDR1 affect enzyme activity or gene expression of proteins and may alter plasma pantoprazole concentrations and treatment success in PUD. In this study, we aimed to investigate the association between genetic polymorphisms in CYP2C19, CYP3A4 and MDR1 and pharmacokinetics of pantoprazole and therapeutic outcome in patients with either Helicobacter pylori-associated [H.P.(+)]-PUD or [H.P.(+)]-gastritis. The plasma pantoprazole concentrations were determined by using an HPLC method at the third hour after a 40-mg tablet of pantoprazole administration in 194 newly diagnosed patients with either [H.P.(+)]-PUD or [H.P.(+)]-gastritis. Genotyping was performed by using PCR-RFLP and DNA sequencing. Among patients appearing for follow-up examination (n = 105), the eradication rate for H. pylori was 82.8% (n = 87). The median pantoprazole plasma concentrations in poor metabolizers (PM), rapid metabolizers (RM) and ultrarapid metabolizers (URM) were 2.07, 1.69 and 1.28 μg/ml, respectively (p = 0.04). CYP3A4*1G and *22 polymorphisms did not affect plasma pantoprazole concentrations and H. pylori eradication rate. The MDR1 genetic polymorphisms did not affect plasma pantoprazole concentrations. MDR1 3435CC-2677GG-1236CC haplotype carriers had lower H. pylori eradication rate (60%) than the remaining subjects (84.9%) while the difference was not statistically significant (p = 0.07). In conclusion, while CYP2C19 genetic polymorphisms significantly affected plasma pantoprazole concentrations, polymorphisms of CYP2C19, CYP3A4 and MDR1 did not affect H. pylori eradication rates.

Rapid and ultra-rapid metabolizers with CYP2C19*17 polymorphism do not respond to standard therapy with proton pump inhibitors

Introduction and objective

Polymorphisms in genes encoding drug metabolizing enzymes may lead to varied enzyme activity and inter-individual variability in drug efficacy and/or toxicity. Since CYP2C19 and CYP3A4 genes code for enzymes involved in metabolizing wide variety of drugs including proton pump inhibitors, we sought to identify polymorphisms in these genes in order to study their impact on drug metabolism in subjects.

Methods

DNA was isolated from healthy individuals including tribals and genotyped for 11 single nucleotide polymorphisms in CYP2C19 and 6 polymorphisms in CYP3A4. Individuals were categorized into different phenotypes based on their drug metabolizing genotype. Volunteers from each group were administered proton pump inhibitors (Esomeprazole, Pantoprazole; 40 mg/day) for 5 days followed by pharmacokinetic studies and measurement of intra-gastric pH.

Results

Of the 17 polymorphisms studied, only CYP2C19*2,*3,*17 and CYP3A4*1B polymorphisms were observed. In comparison to urban individuals, a significantly (p = 0.0003) higher number of poor metabolizers were noted in the tribal individuals. Pantoprazole was found to be most effective in poor metabolizers in terms of area under the curve and Tmax. No significant difference was observed in the intra-gastric pH at baseline and day 6 in rapid and ultra-rapid metabolizers.

Conclusion

Our study has demonstrated that 19.7% of our subjects are carriers of the CYP2C19*17 allele who did not respond to the standard dose of proton pump inhibitors. Genetic screening to identify subjects with variant alleles would thus be useful for personalization of therapy with proton pump inhibitors.

•

Frequency of poor metabolizers varies significantly in two distinct ethnic groups studied.

•

Subjects with CYP2C19*17 polymorphism are not responsive to standard PPI dose.

•

Identifying individuals with these variants may aid in tailoring drug dose for hyper acidic conditions.

Lansoprazole Is Associated with Worsening Asthma Control in Children with the CYP2C19 Poor Metabolizer Phenotype

RATIONALE

Gastric acid blockade in children with asymptomatic acid reflux has not improved asthma control in published studies. There is substantial population variability regarding metabolism of and response to proton pump inhibitors based on metabolizer phenotype. How metabolizer phenotype affects asthma responses to acid blockage is not known.

OBJECTIVES

To determine how metabolizer phenotype based on genetic analysis of CYP2C19 affects asthma control among children treated with a proton pump inhibitor.

METHODS

Asthma control as measured by the Asthma Control Questionnaire (ACQ) and other questionnaires from a 6-month clinical trial of lansoprazole in children with asthma was analyzed for associations with surrogates of lansoprazole exposure (based on treatment assignment and metabolizer phenotype). Groups included placebo-treated children; lansoprazole-treated extensive metabolizers (EMs); and lansoprazole-treated poor metabolizers (PMs). Metabolizer phenotypes were based on CYP2C19 haplotypes. Carriers of the CYP2C19*2, *3, *8, *9, or *10 allele were PMs; carriers of two wild-type alleles were extensive metabolizers (EMs).

MEASUREMENTS AND MAIN RESULTS

Asthma control through most of the treatment period was unaffected by lansoprazole exposure or metabolizer phenotype. At 6 months, PMs displayed significantly worsened asthma control compared with EMs (+0.16 vs. -0.13; P = 0.02) and placebo-treated children (+0.16 vs. -0.23; P < 0.01). Differences in asthma control were not associated with changes in gastroesophageal reflux symptoms. Recent upper respiratory infection worsened asthma control, and this upper respiratory infection effect may be more pronounced among lansoprazole-treated PMs.

CONCLUSIONS

Children with the PM phenotype developed worse asthma control after 6 months of lansoprazole treatment for poorly controlled asthma. Increased exposure to proton pump inhibitor may worsen asthma control by altering responses to respiratory infections. Clinical trial registered with www.clinicaltrials.gov (NCT00604851).

Pharmacogenomic testing: the case for CYP2C19 proton pump inhibitor gene-drug pairs

The use of proton pump inhibitors (PPIs) in the treatment of gastroesophageal reflux and related diseases is increasing, especially in the pediatric population. Prolonged use of PPIs has been associated with several adverse effects, including potentially life-threatening gastric and respiratory infections, which are related to dose or to the degree of gastric acid suppression. Genetic variation in the CYP2C19 gene gives rise to poor and extensive metabolizer phenotypes, which influence PPI clearance, efficacy and exposure. A recent paper linked lansoprazole-associated respiratory infections in children with the poor metabolizer phenotype. The case is made for implementing pharmacogenomic testing for the CYP2C19-PPI gene-drug pair and to dose accordingly in order to minimize PPI-associated infections.

Interindividual variability of CYP2C19-catalyzed drug metabolism due to differences in gene diplotypes and cytochrome P450 oxidoreductase content

Large interindividual variability has been observed in the metabolism of CYP2C19 substrates in vivo. The study aimed to evaluate sources of this variability in CYP2C19 activity, focusing on CYP2C19 diplotypes and the cytochrome P450 oxidoreductase (POR). CYP2C19 gene analysis was carried out on 347 human liver samples. CYP2C19 activity assayed using human liver microsomes confirmed a significant a priori predicted rank order for (S)-mephenytoin hydroxylase activity of CYP2C19*17/*17 > *1B/*17 > *1B/*1B > *2A/*17 > *1B/*2A > *2A/*2A diplotypes. In a multivariate analysis, the CYP2C19*2A allele and POR protein content were associated with CYP2C19 activity. Further analysis indicated a strong effect of the CYP2C19*2A, but not the *17, allele on both metabolic steps in the conversion of clopidogrel to its active metabolite. The present study demonstrates that interindividual variability in CYP2C19 activity is due to differences in both CYP2C19 protein content associated with gene diplotypes and the POR concentration.

Evaluation of the relationship between polymorphisms in CYP2C19 and the pharmacokinetics of omeprazole, pantoprazole and rabeprazole

AIM

To evaluate the possible association between polymorphisms in CYP2C19 and the pharmacokinetics of omeprazole, rabeprazole and pantoprazole.

MATERIALS & METHODS

151 healthy volunteers were evaluated for polymorphisms in the CYP2C19 gene using real-time polymerase chain reaction. Plasma concentrations were measured using high-performance liquid chromatography coupled to mass spectrometry.

RESULTS

Carriers of the *2 allele displayed poor metabolism for all the PPIs studied (around 50% decrease in clearance). Subjects with the *17 allele showed a light increase in clearance compared with *1/*1 (not significant).

CONCLUSION

CYP2C19*2 is associated with decreased clearance of all the PPIs, that could be associated with higher drug efficacy. CYP2C19*17 could increase clearance of these drugs, although the effect seems small.

Influence of CYP2D6 and CYP2C19 genetic polymorphism on the pharmacokinetics of tolperisone in healthy volunteers

PURPOSE

This is the first study that connects pharmacokinetics of tolperisone with genetic polymorphism of the enzymes involved in its metabolism in human. We aimed to identify the influence of polymorphism of two main enzymes (CYP2D6 and CYP2C19) on pharmacokinetic profile of parent drug.

METHODS

In a single-dose study, 28 healthy Caucasian male volunteers received an oral dose of 150 mg of tolperisone. The subjects were genotyped with respect to CYP2D6 and CYP2C19 enzymes. Plasma was sampled for up to 12 h post dose, followed by quantification of tolperisone by a fully validated HPLC-tandem mass spectrometry (MS/MS) method. The pharmacokinetic parameters were estimated using a non-compartmental method and compared statistically at level p < 0.05 across the genotyped groups.

RESULTS

High variability (exceeded 100%) of main bioavailability parameters (AUCt, AUC(inf), C(max)) was observed in the whole group of subjects. An essential difference in the pharmacokinetics of tolperisone of quick metabolizers whose genotype expressed wild homozygote CYP2D6 *1/*1 with respect to heterozygous *1/*4 and *1/*5 subjects was demonstrated. The mean AUC(inf) was 2.1- and 3.4-fold higher in *1/*4 and *1/*5, respectively, than in *1/*1 subjects. In case of Cmax, the differences were greater and reached maximally 3.8 times (mean values 54.00, 98.85, and 205.20 ng/mL for CYP2D6 *1/*1, *1/*4, and *1/*5, respectively). Values of the parameters for the one subject that expressed *4/*4 genotype were even 8.5 times higher than in subjects with extensive or intermediate phenotype. Although CYP2C19 *1/*2 subjects had higher AUCt, AUC(inf), and Cmax values than *1/*1, no statistically significant differences were observed. Oral clearance (CL/F) significantly decreased by 65.7% in heterozygous *1/*2 relative to homozygous *1/*1 extensive metabolizers.

CONCLUSION

In this study, we first demonstrated the effect of CYP2D6 polymorphism on pharmacokinetics of tolperisone in Caucasian subjects. The contribution of CYP2C19 enzyme seems to be less important.

Prediction of in vivo clearance and associated variability of CYP2C19 substrates by genotypes in populations utilizing a pharmacogenetics-based mechanistic model

It is important to examine the cytochrome P450 2C19 (CYP2C19) genetic contribution to drug disposition and responses of CYP2C19 substrates during drug development. Design of such clinical trials requires projection of genotype-dependent in vivo clearance and associated variabilities of the investigational drug, which is not generally available during early stages of drug development, but is essential for CYP2C19 substrates with multiple clearance pathways. This study evaluated the utility of pharmacogenetics-based mechanistic modeling in predicting such parameters. Hepatic CYP2C19 activity and variability within genotypes were derived from in vitro S-mephenytoin metabolic activity in genotyped human liver microsomes (N = 128). These data were then used in mechanistic models to predict genotype-dependent disposition of CYP2C19 substrates (i.e., S-mephenytoin, citalopram, pantoprazole, and voriconazole) by incorporating in vivo clearance or pharmacokinetics of wild-type subjects and parameters of other clearance pathways. Relative to the wild-type, the CYP2C19 abundance (coefficient of variation percentage) in CYP2C19*17/*17, *1/*17, *1/*1, *17/null, *1/null, and null/null microsomes was estimated as 1.85 (117%), 1.79 (155%), 1.00 (138%), 0.83 (80%), 0.38 (130%), and 0 (0%), respectively. The subsequent modeling and simulations predicted, within 2-fold of the observed, the means and variabilities of urinary S/R-mephenytoin ratio (36 of 37 genetic groups), the oral clearance of citalopram (9 of 9 genetic groups) and pantoprazole (6 of 6 genetic groups), and voriconazole oral clearance (4 of 4 genetic groups). Thus, relative CYP2C19 genotype-dependent hepatic activity and variability were quantified in vitro and used in a mechanistic model to predict pharmacokinetic variability, thus allowing the design of pharmacogenetics and drug-drug interaction trials for CYP2C19 substrates.

Influence of CYP2C19 loss-of-function variants on the metabolism of clopidogrel in patients from north-western China

WHAT IS KNOWN AND OBJECTIVE

Variation of the cytochrome P450 2C19 gene coding for the CYP2C19 enzyme has been reported to be associated with clopidogrel response variability. The activity of the CYP2C19 enzyme is genetically influenced by polymorphisms of its gene.

METHODS

This study was conducted to assess the impact of CYP2C19 polymorphism on the clopidogrel metabolism, indirectly selecting the plasma concentration ratios of clopidogrel to its inactive metabolite SR26334 as an evaluation index. Genotyping and plasma concentration results of 366 patients on clopidogrel maintenance therapy (75 mg daily dose) were analysed in this study. CYP2C19 genotypes were determined by PCR-restriction fragment length polymorphism method.

RESULTS AND DISCUSSION

As for CYP2C19, patients were classified into three metabolism genotype groups: EM (44·3%), IM (43·4%) and PM (12·3%). The mean plasma concentration ratio of clopidogrel to its inactive metabolite SR26334 for the entire sample was 0·507. The plasma concentration ratios of the 3 metabolism groups were significantly different (P < 0·001). The lowest plasma concentration ratio value was observed for PM patients.

WHAT IS NEW AND CONCLUSION

Polymorphism of CYP2C19 was significantly associated with plasma concentration ratios of clopidogrel to its inactive metabolite SR26334. Clopidogrel metabolism was regulated by CYP2C19. The *2 and *3 allele carriage were independently associated with the antiplatelet effect of chronic clopidogrel therapy.

Gene variants in CYP2C19 are associated with altered in vivo bupropion pharmacokinetics but not bupropion-assisted smoking cessation outcomes

Bupropion is used clinically to treat depression and to promote smoking cessation. It is metabolized by CYP2B6 to its active metabolite hydroxybupropion, yet alterations in CYP2B6 activity have little impact on bupropion plasma levels. Furthermore, less than 10% of a bupropion dose is excreted as urinary bupropion and its characterized metabolites hydroxybupropion, threohydrobupropion, and erythrohydrobupropion, suggesting that alternative metabolic pathways may exist. In vitro data suggested CYP2C19 could metabolize bupropion. The current study investigated the impact of functional CYP2C19 genetic variants on bupropion pharmacokinetics and treatment outcomes. In 42 healthy volunteers, CYP2C19*2 (a reduced activity allele) was associated with higher bupropion area under the plasma concentration-time curve (AUC), but similar hydroxybupropion AUC. The mean bupropion AUC was 771 versus 670 hours⋅ng/ml in individuals with and without CYP2C19*2, respectively (P = 0.017). CYP2C19*2 was also associated with higher threohydrobupropion and erythrohydrobupropion AUC (P < 0.005). Adjusting for CYP2B6 genotype did not alter these associations, and CYP2C19 variants did not alter the utility of the hydroxybupropion/bupropion ratio as a measure of CYP2B6 activity. Finally, in a clinical trial of 540 smokers, CYP2C19 genotype was not associated with smoking cessation outcomes, supporting the hypothesis that bupropion response is mediated by hydroxybupropion, which is not altered by CYP2C19. In conclusion, our study reports the first in vivo evidence that reduced CYP2C19 activity significantly increases the steady-state exposure to bupropion and its reductive metabolites threohydrobupropion and erythrohydrobupropion. These pharmacokinetic changes were not associated with differences in bupropion's ability to promote smoking cessation in smokers, but may influence the side effects and toxicity associated with bupropion.

Effects of proton pump inhibitors on metformin pharmacokinetics and pharmacodynamics

As inhibitors of organic cation transporters (OCTs), proton pump inhibitors (PPIs) may affect the plasma levels of metformin, an OCT substrate. We investigated the effects of two PPIs, pantoprazole and rabeprazole, on metformin pharmacokinetics and glucose levels in healthy subjects. In this open, randomized, six-sequence, three-period crossover study, 24 participants were administered metformin, either alone or in combination with pantoprazole or rabeprazole. The plasma concentrations of metformin and serum concentrations of glucose after a 75-g oral glucose tolerance test (OGTT) were determined. The area under the concentration-time curve (AUC) for metformin was 15% and 16% greater following coadministration with pantoprazole and rabeprazole, respectively. The maximum plasma metformin concentrations (Cmax) also increased by 15% and 22%, respectively, compared with when it was administered without the PPIs. The percentage change in the AUC for glucose concentration versus time for metformin plus rabeprazole was significantly lower than that for metformin plus pantoprazole [geometric mean ratio: 0.96 (90% confidence interval: 0.92-0.99) and 0.77 (0.63-0.93), respectively]. There was no significant difference in the maximum glucose concentration. In conclusion, concomitant administration of PPIs with metformin significantly increased plasma metformin exposure, but the effects on glucose disposition were minor and varied depending on the PPI administered.

Investigation of CYP2C19 allele and genotype frequencies in Iranian population using experimental and computational approaches

CytochromeP4502C19 is a genetically polymorphic gene with prominent role in drug metabolism. Regarding its critical medical importance, this study was conducted to achieve accurate CYP2C19allele frequencies in Iranian population and hereby paving the way for a tailor-made CYP2C19 DNA test. Iran is a large multi-ethnic country, however, its population structure for CYP2C19 alleles is calculated as nearly zero (Fwc (st)=0.001). The Study was conducted on 691 individuals in Tehran, the conurbation in which total population structure is significantly eroded by massive immigration and DNA was analyzed by TaqMan SNP genotyping assay. A cumulative meta-analysis was then conducted to achieve less than five percent variation range in allele frequencies with 99.9% confidence level. High degree of Hardy-Weinberg equilibrium in pooled data proved the authenticity of meta-analysis. By cumulative meta-analysis the average frequencies of CYP2C19*2 and CYP2C19*3 alleles were calculated as 0.125[99.9% CI, 0.112-0.139] and 0.006[99.9% CI, 0.004-0.009], respectively. According to the solid frequency data obtained by pooling the data and meta-analysis and comparing with other ethnicities, Iranian population's CYP2C19 allele frequencies completely differ from other Asian ethnicities and matches African and European ethnicities the most. Since this is the biggest CYP2C19 allele frequency study in the Middle East, the results of this study will also be useful in cross-population and regional CYP2C19 genetic variation studies.

Antiplatelet drug interactions with proton pump inhibitors

INTRODUCTION

Non-aspirin antiplatelet agents (e.g., clopidogrel, prasugrel, ticagrelor) are commonly prescribed for the prevention of recurrent cardiovascular events among patients with acute coronary syndromes (ACS) and/or those undergoing percutaneous coronary intervention (PCI). In addition, combination therapy with proton pump inhibitors (PPIs) is often recommended to attenuate gastrointestinal bleeding risk, particularly during dual antiplatelet therapy (DAPT) with clopidogrel and aspirin. Importantly, a pharmacological interaction between clopidogrel and some PPIs has been proposed based on mutual CYP450-dependent metabolism, but available evidence is inconsistent.

AREAS COVERED

This article provides an overview of the currently approved antiplatelet agents and PPIs, including their metabolic pathways. Additionally, the CYP450 isoenzyme at the center of the drug interaction, CYP2C19, is described in detail, and the available evidence on both the potential pharmacological interaction and influence on clinical outcomes are summarized and evaluated.

EXPERT OPINION

Although concomitant DAPT and PPI use reduces clopidogrel active metabolite levels and ex vivo-measured platelet inhibition, the influence of the drug interaction on clinical outcomes has been conflicting and largely reported from non-randomized observational studies. Despite this inconsistency, a clinically important interaction cannot be definitively excluded, particularly among patient subgroups with higher overall cardiovascular risk and potentially among CYP2C19 loss-of-function allele carriers.

Regulatory polymorphisms in CYP2C19 affecting hepatic expression

BACKGROUND

Cytochrome P450 2C19 is responsible for the metabolism of many drugs, including the activation of clopidogrel. The allele CYP2C19*17 is associated with ultra-rapid metabolizer phenotypes by increasing gene transcription. This study tests to what extent CYP2C19*17 enhances CYP2C19 expression in human liver and whether additional regulatory variants contribute to variation in CYP2C19 expression.

METHODS

CYP2C19 mRNA was measured with quantitative real-time PCR (qRT-PCR), enzyme activity as metabolic velocity with S-mephenytoin as the substrate and allelic mRNA expression ratio with SNaPshot in human livers. CYP2C19 transcribed exons and a 4kb promoter region were sequenced using IonTorrent PGM or Sanger sequencing and screened for polymorphisms associated with total hepatic CYP2C19 mRNA, enzyme activity and allelic mRNA ratios.

RESULTS

Livers heterozygote and homozygous for CYP2C19*17 had mRNA levels 1.8-fold (p=0.028) and 2.9-fold (p=0.006), respectively, above homozygous reference allele livers. CYP2C19*17 heterozygotes were also associated with increased allelic mRNA expression (allelic ratio ~1.8-fold, SD±0.6, p<0.005), whereas CYP2C19 enzyme activity was elevated 2.3-fold, with borderline significance (p=0.06) in CYP2C19*17 carriers. One liver sample of African ancestry displayed a 2-fold allelic expression ratio, and another sample, a ~12-fold increase in metabolic velocity. Neither case was accounted for by *17, which indicates the presence of additional regulatory variants.

CONCLUSIONS

Our findings confirm *17 as a regulatory polymorphism enhancing hepatic CYP2C19 expression 2-fold with potential to compensate for the loss of function allele CYP2C19*2. Additional regulatory factors may also enhance CYP2C19 expression in African American populations.

Impact of genetic polymorphisms in CYP2C9 and CYP2C19 on the pharmacokinetics of clinically used drugs

Human cytochrome P450 (CYP) is a superfamily of hemoproteins which oxidize a number of endogenous compounds and xenobiotics. The human CYP2C subfamily consists of four members: CYP2C8, CYP2C9, CYP2C18 and CYP2C19. CYP2C9 and CYP2C19 are important drug-metabolizing enzymes and together metabolize approximately 20% of therapeutically used drugs. Forty-two allelic variants for CYP2C9 and 34 for CYP2C19 have been reported. The frequencies of these variants show marked inter-ethnic variation. The functional consequences of genetic polymorphisms have been examined, and many studies have shown the clinical importance of these polymorphisms. Current evidence suggests that taking the genetically determined metabolic capacity of CYP2C9 and CYP2C19 into account has the potential to improve individual risk/benefit relationships. However, more prospective studies with clinical endpoints are needed before the paradigm of "personalized medicine" based on the variants can be established. This review summarizes the currently available important information on this topic.