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.

Pharmacogenetic Aspects of Drug Metabolizing Enzymes and Transporters in Pediatric Medicine: Study Progress, Clinical Practice and Future Perspectives

As the activity of certain drug metabolizing enzymes or transporter proteins can vary with age, the effect of ontogenetic and genetic variation on the activity of these enzymes is critical for the accurate prediction of treatment outcomes and toxicity in children. This makes pharmacogenetic research in pediatrics particularly important and urgently needed, but also challenging. This review summarizes pharmacogenetic studies on the effects of genetic polymorphisms on pharmacokinetic parameters and clinical outcomes in pediatric populations for certain drugs, which are commonly prescribed by clinicians across multiple therapeutic areas in a general hospital, organized from those with the most to the least pediatric evidence among each drug category. We also further discuss the research status of the gene-guided dosing regimens and clinical implementation of pediatric pharmacogenetics. More and more drug-gene interactions are demonstrated to have clinical validity for children, and pharmacogenomics in pediatrics have shown evidence-based benefits to enhance the efficacy and precision of existing drug dosing regimens in several therapeutic areas. However, the most important limitation to the implementation is the lack of high-quality, rigorous pediatric prospective clinical studies, so adequately powered interventional clinical trials that support incorporation of pharmacogenetics into the care of children are still needed.

Perspectives from the Society for Pediatric Research: pharmacogenetics for pediatricians

This review evaluates the pediatric evidence for pharmacogenetic associations for drugs that are commonly prescribed by or encountered by pediatric clinicians across multiple subspecialties, organized from most to least pediatric evidence. We begin with the pharmacogenetic research that led to the warning of increased risk of death in certain pediatric populations ("ultrarapid metabolizers") who are prescribed codeine after tonsillectomy or adenoidectomy. We review the evidence for genetic testing for thiopurine metabolism, which has become routine in multiple pediatric subspecialties. We discuss the pharmacogenetic research in proton pump inhibitors, for which clinical guidelines have recently been made available. With an increase in the prevalence of behavioral health disorders including attention deficit hyperactivity disorder (ADHD), we review the pharmacogenetic literature on selective serotonin reuptake inhibitors, selective norepinephrine reuptake inhibitors, and ADHD medications. We will conclude this section on the current pharmacogenetic data on ondansetron. We also provide our perspective on how to integrate the current research on pharmacogenetics into clinical care and what further research is needed. We discuss how institutions are managing pharmacogenetic test results and implementing them clinically, and how the electronic health record can be leveraged to ensure testing results are available and taken into consideration when prescribing medications. IMPACT: While many reviews of pharmacogenetics literature are available, there are few focused on pediatrics. Pediatricians across subspecialties will become more comfortable with pharmacogenetics terminology, know resources they can use to help inform their prescribing habits for drugs with known pharmacogenetic associations, and understand the limitations of testing and where further research is needed.

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.

New Guidance on Cytochrome P450 2C19 Phenotype-based Use of Proton Pump Inhibitors

Since the approval of the first proton pump inhibitor (PPI) in 1989, our knowledge regarding this class of medications has further developed. An increasing amount of data now supports the association between cytochrome P450 2C19 (CYP2C19) phenotype and PPI safety and efficacy. This includes pediatric studies, such as those published here and in other pediatric journals within the past year. Moreover, the most recent pediatric Helicobacter pylori guidelines stated that using the PPIs that are less dependent on CYP2C19 for inactivation may be preferred for H pylori eradication among populations that are more likely to have rapid clearance of CYP2C19-metabolized PPIs. Conversely, pantoprazole package insert recommends a dose reduction in known pediatric CYP2C19 poor metabolizers (PMs), citing a 6-fold increase in serum concentrations compared with normal metabolizers (NMs). The purpose of this communication is to introduce a recently published Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for CYP2C19 and PPI dosing.

Raft-forming system for pantoprazole and domperidone delivery: in vitro and in vivo study

The raft is an emerging drug delivery system that not only provides rapid relief from reflux disorders, but also sustains drug release. The objective of this work was to develop and characterize raft-forming bilayer tablets in which pantoprazole sodium sesquihydrate (PSS) was targeted at sustained release and domperidone maleate (DM) was used to obtain an immediate-release effect and perform pharmacokinetic studies. Tablets were prepared using the wet granulation method. Rafts were characterized in terms of strength, weight, volume, resilience, acid-neutralizing capacity, floating lag time and total floating time. Dissolution studies were performed using simulated gastric fluid with pH 1·2. Compatibility were performed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction and differential scanning calorimetry (DSC). Percentage release of the optimized R7 formulation was 94% for PSS and 98% for DM. First-order release kinetics were followed and a non-Fickian diffusion was observed; the value of n was greater than 0·7 in the Korsmeyer–Peppas model. FTIR and DSC studies showed chemical and thermal stability between the drug and polymers. C max values of the test and reference formulations of PSS were 46·080 ± 0·567, 46·350 ± 0·507 and DM were 14·090 ± 1·678 and 10·560 ± 1·098 μg/ml, respectively.

Development and validation of high-performance liquid chromatography method for the simultaneous monitoring of pantoprazole sodium sesquihydrate and domperidone maleate in plasma and its application to pharmacokinetic study

A sensitive, inexpensive high-performance liquid chromatography–ultraviolet detection (HPLC–UV) method has been developed and validated for the simultaneous monitoring of pantoprazole sodium sesquihydrate (PSS) and domperidone maleate (DM) in rabbit plasma on a C18 column with UV detection at 285 nm. Box–Behnken design was used with 3 independent variables, namely, flow rate (X1), mobile phase composition (X2), and phosphate buffer pH (X3), which were used to design mathematical models. Response surface design was applied to optimize the dependent variables, i.e., retention time (Y1 and Y2) and percentage recoveries (Y3 and Y4) of PSS and DM. The method was sensitive and reproducible over 1.562 to 25 μg/mL. The effect of the quadratic outcome of flow rate, mobile phase composition, and buffer pH on retention time (p ˂ 0.001) and percentage recoveries of PSS and DM (p = 0.0016) were significant. The regression values obtained from analytical curve of PSS and DM were 0.999 and 0.9994, respectively. The percentage recoveries of PSS and DM were ranged from 94.5 to 100.41% and 94.77 to 100.31%, respectively. The developed method was applied for studying the pharmacokinetics of PSS and DM. The Cmax of test and reference formulations were 48.06 ± 0.347 μg/mL and 46.31 ± 0.398 μg/mL for PSS, and 15.11 ± 1.608 μg/mL and 12.06 ± 1.234 μg/mL for DM, respectively.

Gene-Based Dose Optimization in Children

Pharmacogenetics is a key component of precision medicine. Genetic variation in drug metabolism enzymes can lead to variable exposure to drugs and metabolites, potentially leading to inefficacy and drug toxicity. Although the evidence for pharmacogenetic associations in children is not as extensive as for adults, there are several drugs across diverse therapeutic areas with robust pediatric data indicating important, and relatively common, drug-gene interactions. Guidelines to assist gene-based dose optimization are available for codeine, thiopurine drugs, selective serotonin reuptake inhibitors, atomoxetine, tacrolimus, and voriconazole. For each of these drugs, there is an opportunity to clinically implement precision medicine approaches with children for whom genetic test results are known or are obtained at the time of prescribing. For many more drugs that are commonly used in pediatric patients, additional investigation is needed to determine the genetic factors influencing appropriate dose.

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.

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.

Novel Implementation of Genotype-Guided Proton Pump Inhibitor Medication Therapy in Children: A Pilot, Randomized, Multisite Pragmatic Trial

The efficacy of proton pump inhibitor (PPI) medications is highly dependent on plasma concentrations, which varies considerably due to cytochrome P450 (CYP2C19) genetic variation. We conducted a pragmatic, pilot study of CYP2C19 genotype‐guided pediatric dosing of PPI medications. Children aged 5–17 years old with gastric‐acid‐related conditions were randomized to receive either conventional dosing of a PPI or genotype‐guided dosing for a total of 12 weeks. Sixty children (30 in each arm) were enrolled and had comparable baseline characteristics. The mean daily omeprazole equivalent dose prescribed to participants across metabolizer phenotype groups was significantly different in the genotype‐guided dosing arm (P < 0.001), but not in the conventional dosing arm. Prescribers waited for the genotype result before prescribing the PPI medication for 90% of the participants in the genotype‐guided dosing arm. The number of participants who reported an infection was marginally lower in genotype‐guided dosing vs. conventional dosing (20% vs. 44%; P = 0.07). Sinonasal symptoms were higher in the conventional dosing arm as compared with genotype‐guided dosing arm: (2.6 (2.0, 3.4) vs. 1.8 (1.0, 2.3), P = 0.031). CYP2C19 genotype‐guided PPI therapy is feasible in a clinical pediatric setting, well accepted by providers, resulted in differential PPI dosing, and may reduce PPI‐associated infections. A future large scale randomized clinical trial of CYP2C19 genotype‐guided pediatric dosing of PPI medications in children is warranted.

Development and pharmacokinetic evaluation of alginate-pectin polymeric rafts forming tablets using box behnken design

Raft is an emerging drug delivery system, which is suitable for controlled release drug delivery and targeting. The present study aimed to evaluate the physico-chemical properties of raft, in vitro release of pantoprazole sodium sesquihydrate and conduct bioavailability studies. Box behnken design was used with three independent and dependent variables. Independent variables were sodium alginate (X₁), pectin (X₂) and hydroxypropyl methyl cellulose K100M (X₃) while dependent variables were percentage drug release at 2 (Y₂), 4 (Y₄) and 8 h (Y₈). The developed rafts were evaluated by their physical and chemical properties. Fourier transform infrared spectroscopy and differential scanning calorimetry were used to study the chemical interaction and thermal behaviour of drug with polymers. Alginate and pectin contents of R9 formulation were 99.28% and 97.29%, respectively, and acid neutralization capacity was 8.0. R9 formulation showed longer duration of neutralization and nature of raft was absorbent. The raft of R9 formulation showed 98.94% release of PSS at 8 h in simulated gastric fluid. Fourier transform infrared spectroscopy showed no chemical interaction and differential scanning calorimetry indicated endothermic peaks at 250 °C for pantoprazole sodium sesquihydrate. t_max for the test and reference formulations were 8 ± 2.345 h and 8 ± 2.305 h, respectively. C_max of test and reference formulations were 46.026 ± 0.567 µg/mL and 43.026 ± 0.567 µg/mL, respectively. AUC_(0-t) of the test and reference formulations were 472.115 ± 3.467 µg × h/mL and 456.105 ± 2.017 µg × h/mL, respectively. Raft forming system successfully delivered the drug in controlled manner and improved the bioavailability of drugs.

A Population-Based Pharmacokinetic Model Approach to Pantoprazole Dosing for Obese Children and Adolescents

BACKGROUND AND AIMS

Pharmacokinetic data for proton pump inhibitors (PPIs), acid-suppression drugs commonly prescribed to children, are lacking for obese children who are at greatest risk for acid-related disease. In a recent multi-center investigation, we demonstrated decreased, total body weight adjusted, apparent clearance (CL/F) of the PPI pantoprazole for obese children compared with their non-obese peers. Subsequently, we developed a population-based pharmacokinetic (PopPK) model to characterize pantoprazole disposition and evaluated appropriate pantoprazole dosing strategies for obese pediatric patients, using simulation.

METHODS

Pharmacokinetic data from the only prospective study of PPIs in obese children (aged 6-17 years; n = 40) included 273 pantoprazole and 256 pantoprazole-sulfone plasma concentrations, after single oral-dose administration, and were used for pantoprazole model development and covariate analysis (NONMEM®). Model evaluation was performed via bootstrapping and predictive checks, and the final model was applied to simulate systemic pantoprazole exposures for common dosing scenarios.

RESULTS

A two-compartment PopPK model, which included CYP2C19 genotype and total body weight, provided the best fit. Resultant, typical, weight-normalized pantoprazole parameter estimates were different than previously reported for children or adults, with significantly reduced pantoprazole CL/F for obese children. Of the dosing scenarios evaluated, the weight-tiered approach, approved by the US Food and Drug Administration, achieved pantoprazole exposures [area under the curve (AUC0-∞)] within ranges previously reported as therapeutic, without over- or under-prediction for obese children.

CONCLUSIONS

Our data argue against empiric dose escalation of PPIs for obese children and support current FDA-approved pediatric weight-tiered dosing for pantoprazole; however, 3- to 5-fold inter-individual variability in pantoprazole AUC0-∞ remained using this dosing approach.

Pantoprazole, an Inhibitor of the Organic Cation Transporter 2, Does Not Ameliorate Cisplatin-Related Ototoxicity or Nephrotoxicity in Children and Adolescents with Newly Diagnosed Osteosarcoma Treated with Methotrexate, Doxorubicin, and Cisplatin

Lessons Learned.

Using a randomized crossover design and continuous variables such as change in hearing threshold and biomarkers of acute renal injury as short‐term endpoints, it was determined that pantoprazole, an organic cation transporter 2 inhibitor, did not ameliorate cisplatin‐associated nephrotoxicity or ototoxicity.

Cystatin C is a robust method to estimate glomerular filtration rate in patients with cancer. Using a patient‐reported outcome survey, all patients identified tinnitus and subjective hearing loss occurring “at least rarely” after cycle 1, prior to objective high‐frequency hearing loss measured by audiograms.

New therapies that improve outcome with less acute and long‐term toxicity are needed.

Background.

Organic cation transporter 2 (OCT2), which is a cisplatin uptake transporter expressed on renal tubules and cochlear hair cells but not on osteosarcoma cells, mediates cisplatin uptake. Pantoprazole inhibits OCT2 and could ameliorate cisplatin ototoxicity and nephrotoxicity. Using a randomized crossover design, we evaluated audiograms, urinary acute kidney injury (AKI) biomarkers, and glomerular filtration rate (GFR) estimated from cystatin C (GFR_cysC) in patients receiving cisplatin with and without pantoprazole.

Materials and Methods.

Cisplatin (60 mg/m² × 2 days per cycle) was administered concurrently with pantoprazole (intravenous [IV], 1.6 mg/kg over 4 hours) on cycles 1 and 2 or cycles 3 and 4 in 12 patients with osteosarcoma (OS) with a median (range) age of 12.8 (5.6–19) years. Audiograms, urinary AKI biomarkers, and serum cystatin C were monitored during each cycle.

Results.

Pantoprazole had no impact on decrements in hearing threshold at 4–8 kHz, post‐treatment elevation of urinary AKI biomarkers, or GFR_cysC (Fig. 1, Table 1). Histological response (percent necrosis) after two cycles was similar with or without pantoprazole. All eight patients with localized OS at diagnosis are alive and in remission; three of four patients with metastases at diagnosis have died.

Conclusion.

Pantoprazole did not ameliorate cisplatin ototoxicity or nephrotoxicity. The decrease in GFR_cysC and increase in N‐acetyl‐ß‐glucosaminidase (NAG) and creatinine demonstrate that these biomarkers can quantify cisplatin glomerular and proximal tubular toxicity. OCT2 inhibition by pantoprazole did not appear to alter antitumor response or survival.

Obese Children Require Lower Doses of Pantoprazole Than Nonobese Peers to Achieve Equal Systemic Drug Exposures

OBJECTIVE

To assess appropriate pantoprazole dosing for obese children, we conducted a prospective pharmacokinetics (PK) investigation of pantoprazole in obese children, a patient population that is traditionally excluded from clinical trials.

STUDY DESIGN

A total of 41 obese children (6-17 years of age), genotyped for CYP2C19 variants *2, *3, *4, and *17, received a single oral dose of pantoprazole, ~1.2 mg/kg lean body weight (LBW), with LBW calculated via a validated formula. Ten post-dose pantoprazole plasma concentrations were measured, and PK variables generated via noncompartmental methods (WinNonlin). Linear and nonlinear regression analyses and analyses of variance were used to explore obesity, age, and CYP2C19 genotype contribution to pantoprazole PK. PK variables of interest were compared with historic nonobese peers treated with pantoprazole.

RESULTS

Independent of genotype, when normalized to dose per kg total body weight, pantoprazole apparent clearance and apparent volume of distribution were significantly lower (P < .05) and systemic exposure significantly higher (P < .01) in obese vs nonobese children. When normalized per kg LBW, these differences were not evident in children ≥12 years of age and markedly reduced in children <12 years of age.

CONCLUSIONS

LBW dosing of pantoprazole led to pantoprazole PK similar to nonobese peers. Additional factors, other than body size (eg, age-related changes in CYP2C19 activity), appear to affect pantoprazole PK in children <12 years of age.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02186652.

Clinical Pharmacogenetics of Cytochrome P450-Associated Drugs in Children

Cytochrome P450 (CYP) enzymes are commonly involved in drug metabolism, and genetic variation in the genes encoding CYPs are associated with variable drug response. While genotype-guided therapy has been clinically implemented in adults, these associations are less well established for pediatric patients. In order to understand the frequency of pediatric exposures to drugs with known CYP interactions, we compiled all actionable drug-CYP interactions with a high level of evidence using Clinical Pharmacogenomic Implementation Consortium (CPIC) data and surveyed 10 years of electronic health records (EHR) data for the number of children exposed to CYP-associated drugs. Subsequently, we performed a focused literature review for drugs commonly used in pediatrics, defined as more than 5000 pediatric patients exposed in the decade-long EHR cohort. There were 48 drug-CYP interactions with a high level of evidence in the CPIC database. Of those, only 10 drugs were commonly used in children (ondansetron, oxycodone, codeine, omeprazole, lansoprazole, sertraline, amitriptyline, citalopram, escitalopram, and risperidone). For these drugs, reports of the drug-CYP interaction in cohorts including children were sparse. There are adequate data for implementation of genotype-guided therapy for children for three of the 10 commonly used drugs (codeine, omeprazole and lansoprazole). For the majority of commonly used drugs with known CYP interactions, more data are required to support pharmacogenomic implementation in children.

Pediatric intensive care stress ulcer prevention (PIC-UP): a protocol for a pilot randomized trial

Background

Despite sparse pediatric data on effectiveness, the majority of critically ill children receive medications to prevent gastrointestinal (GI) bleeding. Stress ulcer prophylaxis may have unintended consequences—increasing the risk of nosocomial infections—which may be more serious and common than the bleeding which these drugs are prescribed to prevent. Randomized controlled trials (RCTs) in pediatric critical care are exceptionally challenging to complete, thus a rigorous pilot RCT is crucial. The objective of this pilot RCT is to assess the feasibility of a large multicentre RCT of stress ulcer prophylaxis with pantoprazole to prevent upper GI bleeding vs. placebo.

Methods

A multi-centre blinded pilot RCT of 120 children in six Canadian PICUs. Children expected to require mechanical ventilation for more than 48 h will be randomized to receive intravenous pantoprazole 1 mg/kg or identical placebo once daily until they no longer need mechanical ventilation. We have four feasibility outcomes and will consider the trial successful if we achieve:

Effective screening: If >80% of eligible patients are approached for consent.

Timely enrollment: if >80% of participants receive their first dose of the assigned study drug within 1 day of becoming eligible.

Participant accrual: If the average monthly enrolment is two or more participants per centre per month.

Protocol adherence: if >90% of doses are administered according to the protocol.

Discussion

There are many uncertainties about the risks and benefits of stress ulcer prophylaxis. In an era of widespread use—where clinicians prescribe prophylaxis to the more severely ill—a large, rigorous RCT is required. A trial to determine if a strategy of withholding stress ulcer prophylaxis is not inferior to a strategy of routine stress ulcer prophylaxis will be challenging. A carefully designed and implemented pilot trial is essential.

Trial registration

ClinicalTrials.gov:NCT02929563 (Registered October 3, 2016).

Pediatric perspective on pharmacogenomics

The advances in high-throughput genomic technologies have improved the understanding of disease pathophysiology and have allowed a better characterization of drug response and toxicity based on individual genetic make up. Pharmacogenomics is being recognized as a valid approach used to identify patients who are more likely to respond to medication, or those in whom there is a high probability of developing severe adverse drug reactions. An increasing number of pharmacogenomic studies are being published, most include only adults. A few studies have shown the impact of pharmacogenomics in pediatrics, highlighting a key difference between children and adults, which is the contribution of developmental changes to therapeutic responses across different age groups. This review focuses on pharmacogenomic research in pediatrics, providing examples from common pediatric conditions and emphasizing their developmental context.

Proton pump inhibitors in pediatrics : mechanism of action, pharmacokinetics, pharmacogenetics, and pharmacodynamics

Proton pump inhibitors (PPIs) have become some of the most frequently prescribed medications for treatment of adults and children. Their effectiveness for treatment of peptic conditions in the pediatric population, including gastric ulcers, gastroesophageal reflux disease (GERD), and Helicobacter pylori infections has been established for children older than 1 year. Studies of the preverbal population of neonates and infants have identified doses that inhibit acid production, but the effectiveness of PPIs in the treatment of GERD has not been established except for the recent approval of esomeprazole treatment of erosive esophagitis in infants. Reasons that have been proposed for this are complex, ranging from GERD not occurring in this population to a lack of histologic identification of esophagitis related to GERD to questions about the validity of symptom scoring systems to identify esophagitis when it occurs in infants. The effectiveness of PPIs relates to their structures, which must undergo acidic activation within the parietal cell to allow the PPI to be ionized and form covalent disulfide bonds with cysteines of the H(+)-K(+)-adenosine triphosphatase (H(+)-K(+)-ATPase). Once the PPI binds to the proton pump, the pump is inactivated. Some PPIs, such as omeprazole and rabeprazole bind to cysteines that are exposed, and their binding can be reversed. After irreversible chemical inhibition of the proton pump, such as occurs with pantoprazole, the recovery of the protein of the pump has a half-life of around 50 h. Cytochrome P450 (CYP) 2C19 and to a lesser degree CYP3A4 clear the PPIs metabolically. These enzymes are immature at birth and reach adult levels of activity by 5-6 months after birth. This parallels studies of the maturation of CYP2C19 to adult levels by roughly the same age after birth. Specific single nucleotide polymorphisms of CYP2C19 reduce clearance proportionally and increase exposure and prolong proton pump inhibition. Prolonged treatment of pediatric patients with PPIs has not caused cancer or significant abnormalities.

Phase I, multicenter, randomized, open-label study evaluating the pharmacokinetics and safety profile of repeated once-daily doses of intravenous esomeprazole in children 0 to 17 years of age

BACKGROUND

Several oral proton pump inhibitors (PPIs) are currently approved for use in pediatric patients in North America and Europe. However, when use of oral therapy is not possible or appropriate, intravenous formulations of PPIs may be helpful. Intravenous esomeprazole is approved in the United States for the short-term treatment of gastroesophageal reflux disease (GERD) with erosive esophagitis in adults and in pediatric patients 1 month to 17 years of age (inclusive) as an alternative to oral therapy. Four open-label, randomized, 2-way crossover studies in adults with GERD found no clinically relevant differences in acid suppression between repeated doses of oral and intravenous esomeprazole. However, the pharmacokinetics of intravenous esomeprazole has not been studied extensively in children.

OBJECTIVE

The aim of this study was to evaluate steady-state pharmacokinetics and tolerability of repeated doses of intravenous esomeprazole in children.

METHODS

In this multicenter, open-label study, hospitalized patients (0-17 years of age) considered for acid suppression therapy received once-daily intravenous esomeprazole sodium for injection at 0.5 mg/kg (0-1 month of age), 1.0 mg/kg (1-11 months of age), 10 mg (1-5 years of age), 10 or 20 mg (6-11 years of age), or 20 or 40 mg (12-17 years of age) for 4 days. Children 6 to 11 years of age (inclusive) were randomized in a 1:1 ratio to receive esomeprazole 10 or 20 mg, and adolescents 12 to 17 years of age (inclusive) were randomized in a 1:1 ratio to receive esomeprazole 20 or 40 mg. Blood samples were drawn pre- and post-dose. Plasma esomeprazole was measured using reversed-phase liquid chromatography and mass spectrometry. Pharmacokinetic variables were derived using mixed-effects modeling. Adverse events (AEs) were assessed.

RESULTS

Fifty-nine patients were randomized and 57 received the study drug. A majority of patients were white (44 white, 5 black/African American, 3 Asian, 5 other) and male (35/57). Fifty patients were eligible for pharmacokinetic analysis, including 6 to 8 patients in each age group. Esomeprazole pharmacokinetics was dose proportional and related to weight and age. Clearance increased with increasing weight and age. The mean AUC(τ) ranged from 6.9 μmol · h/L (10 mg, 6-11 years) to 17.6 μmol · h/L (40 mg, 12-17 years). The mean C(ss,max) ranged from 3.7 μmol/L (0.5 mg/kg, 0-1 month) to 10.5 μmol/L (40 mg, 12-17 years). Thirty-one patients experienced 1 or more AEs; 6 patients experienced 1 or more treatment-unrelated serious AEs.

CONCLUSIONS

Intravenous esomeprazole at doses resulting in targeted AUC(τ) and C(ss,max) similar to therapeutic exposure in adults appeared to be reasonably well tolerated in this small, select pediatric population. ClinicalTrials.gov identifier: NCT00474019.

Innovative clinical trial design for pediatric therapeutics

Until approximately 15 years ago, sponsors rarely included children in the development of therapeutics. US and European legislation has resulted in an increase in the number of pediatric trials and specific label changes and dosing recommendations, although infants remain an understudied group. The lack of clinical trials in children is partly due to specific challenges in conducting trials in this patient population. Therapeutics in special populations, including premature infants, obese children and children receiving extracorporeal life support, are even less studied. National research networks in Europe and the USA are beginning to address some of the gaps in pediatric therapeutics using novel clinical trial designs. Recent innovations in pediatric clinical trial design, including sparse and scavenged sampling, population pharmacokinetic analyses and 'opportunistic' studies, have addressed some of the historical challenges associated with clinical trials in children.

Pharmacokinetics and tolerability of rabeprazole in children 1 to 11 years old with gastroesophageal reflux disease

BACKGROUND

The pharmacokinetics of rabeprazole after a single oral dose and once-daily administration for 5 consecutive days was characterized in children 1 to 11 years old with gastroesophageal reflux disease (GERD).

PATIENTS AND METHODS

The initial 8 patients received rabeprazole sodium (hereafter referred to as rabeprazole) 0.14 mg/kg (part 1); the next 20 patients were randomized to receive 0.5 or 1 mg/kg (part 2) to target concentrations in plasma expected to be safe and effective. Pharmacokinetic parameters of rabeprazole and the thioether metabolite were calculated using noncompartmental methods. Subjective evaluations of GERD severity, rabeprazole short-term effectiveness, palatability, and safety were also characterized.

RESULTS

Rabeprazole concentrations increased in a dose-dependent manner. Little or no accumulation was observed after repeated administration. The results suggest that formation of the thioether is an important metabolic pathway in young patients, which is consistent with adults. Plasma area under the concentration-time curve values of rabeprazole and the metabolite were poorly correlated with individual age and body weight. Furthermore, oral rabeprazole clearance values (not adjusted for weight) were similar to historical adult data. However, weight-adjusted values were higher for the pediatric patients, and approximately 2 to 3 times the milligram per kilogram dose of rabeprazole in these children was necessary to achieve comparable concentrations in adults. Subjective evaluations demonstrated an improvement of GERD symptoms in most patients after rabeprazole treatment.

CONCLUSIONS

Palatability of the formulation was reported to be good or excellent. Rabeprazole was well tolerated, with no notable differences in safety among the dose groups.

A multicenter, randomized, open-label, pharmacokinetics and safety study of pantoprazole tablets in children and adolescents aged 6 through 16 years with gastroesophageal reflux disease

Children with gastroesophageal reflux disease (GERD) may benefit from gastric acid suppression with proton pump inhibitors such as pantoprazole. Effective treatment with pantoprazole requires correct dosing and understanding of the drug's kinetic profile in children. The aim of these studies was to characterize the pharmacokinetic (PK) profile of single and multiple doses of pantoprazole delayed-release tablets in pediatric patients with GERD aged 6 to 11 years (study 1) and 12 to 16 years (study 2). Patients were randomly assigned to receive pantoprazole 20 or 40 mg once daily. Plasma pantoprazole concentrations were obtained at intervals through 12 hours after the single dose and at 2 and 4 hours after multiple doses for PK evaluation. PK parameters were derived by standard noncompartmental methods and examined as a function of both drug dose and patient age. Safety was also monitored. Pantoprazole PK was dose independent (when dose normalized) and similar to PK reported from adult studies. There was no evidence of accumulation with multiple dosing or reports of serious drug-associated adverse events. In children aged 6 to 16 years with GERD, currently available pantoprazole delayed-release tablets can be used to provide systemic exposure similar to that in adults.

Population pharmacokinetic modeling of pantoprazole in pediatric patients from birth to 16 years

The population pharmacokinetics of pantoprazole was characterized in pediatric patients from birth to 16 years using NONMEM and evaluated via bootstrap and predictive check. Data were described using a 2-compartment model with a typical parameterized in terms of clearance (CL) (95% CI) of 1.93 L per hour (1.53, 2.61), given the reference covariates (female, full term, extensive/unknown CYP2C19 metabolizer status, non-African American, 10 kg weight, intravenous or tablet administration). Pantoprazole pharmacokinetic parameters appear to be similar in pediatric patients compared to adults when allometrically scaled. The effect of age on allometrically scaled CL was best described by a sigmoid Emax model with the age effect reaching an asymptote approximately equal to the adult CL by 1 year. CYP2C19 poor metabolizers exhibited reduced CL with the point estimate and 95% CI more than 70% lower than the typical value. Simulations from the final model indicated that the 1.2-mg/kg dose provides the best comparison to adults.

Single-dose, multiple-dose, and population pharmacokinetics of pantoprazole in neonates and preterm infants with a clinical diagnosis of gastroesophageal reflux disease (GERD)

PURPOSE

The pharmacokinetic profile of pantoprazole granules was assessed in neonates and preterm infants with gastroesophageal reflux disease (GERD) in a multicenter, randomized, open-label trial.

METHODS

Patients were randomly assigned to either the pantoprazole 1.25 mg (approx. 0.6 mg/kg) or 2.5 mg (approx. 1.2-mg/kg) group and treated for > or =5 consecutive days. Blood was sampled either at 0, 2, 8, and 18 h postdose or at 0, 1, 4, and 12 h postdose on day 1 and at 3 and 6 h postdose after > or =5 consecutive doses. Cytochrome P450 2C19 (CYP2C19) and CYP3A4 genotypes were determined. Safety was monitored. Population pharmacokinetics (popPK) analyses were conducted using nonlinear mixed-effects modeling.

RESULTS

The popPK modeling of the pantoprazole 1.25 mg and 2.5 mg groups obtained mean (+/-standard deviation) estimates for the area under the plasma concentration versus time curve (AUC) of 3.54 (+/-2.82) and 7.27 (+/-5.30) microg h/mL, respectively, and mean estimates for half-life of 3.1 (+/-1.5) and 2.7 (+/-1.1) h, respectively. Pantoprazole did not accumulate following multiple-dose administration. The two patients with the CYP2C19 poor metabolizer genotype had a substantially higher AUC than extensive metabolizers. No safety-related discontinuations occurred.

CONCLUSIONS

In preterm infants and neonates, pantoprazole granules were generally well tolerated, mean exposures with pantoprazole 2.5 mg were slightly higher than that in adults who received 40 mg. While the half-life was longer, accumulation did not occur.

Pantoprazole: a proton pump inhibitor

Pantoprazole is a proton pump inhibitor (PPI) that binds irreversibly and specifically to the proton pump, thereby reducing gastric acid secretion. Pantoprazole has a relatively long duration of action compared with other PPIs, and a lower propensity to become activated in slightly acidic body compartments. To date, no drug-drug interactions have been identified with pantoprazole in numerous interaction studies. Overall, in the short-term (8-10 weeks) initial treatment of gastro-oesophageal reflux disease (a condition that occurs when the reflux of gastric contents causes troublesome symptoms and/or complications) and long-term (6-24 months) maintenance therapy, oral pantoprazole 20 or 40 mg/day demonstrated similar efficacy to omeprazole, lansoprazole and esomeprazole and greater efficacy than histamine type 2 receptor antagonists. Pantoprazole is also effective in treating and preventing NSAID-related gastric and gastroduodenal injury. The optimal adult oral dose for gastric acid-related disorders is pantoprazole 40 mg once daily. Although data are limited, pantoprazole 20 or 40 mg/day was effective and well tolerated in the treatment of acid-related disorders in children and adolescents. Pantoprazole was also well tolerated in adults with acid-related disorders in short- and long-term studies. Thus, pantoprazole is a valuable agent for the management of acid-related disorders.

Impact of the CYP2C19*17 allele on the pharmacokinetics of omeprazole and pantoprazole in children: evidence for a differential effect

The impact of the CYP2C19*17 allele on the pharmacokinetics of pantoprazole and omeprazole in previously studied children (n = 40) was explored. When pantoprazole area under the plasma concentration versus time curve (AUC) was examined as a function of CYP2C19 genotype, a significantly lower AUC was observed for subjects identified as CYP2C19*1/*1 and *1/*17. For pantoprazole, a statistically significant relationship was observed between CYP2C19 genotype and both dose-corrected AUC (p < 0.0001) and the apparent elimination rate constant (K(el); p = 0.0012); no significant genotype-phenotype relationships were observed for omeprazole.