Assessment of Dosing Strategies for Pediatric Drug Products

Pediatric drug dosing is challenged by the heterogeneity of developing physiology and ethical considerations surrounding a vulnerable population. Often, pediatric drug dosing leverages findings from the adult population; however, recent regulatory efforts have motivated drug sponsors to pursue pediatric-specific programs to meet an unmet medical need and improve pediatric drug labeling. This paradigm is further complicated by the pathophysiological implications of obesity on drug distribution and metabolism and the roles that body composition and body size play in drug dosing. Therefore, we sought to understand the landscape of pediatric drug dosing by characterizing the dosing strategies from drug products recently approved for pediatric indications identified using FDA Drug Databases and analyze the impact of body size descriptors (age, body surface area, weight) on drug pharmacokinetics for several selected antipsychotics approved in pediatric patients. Our review of these pediatric databases revealed a dependence on body size-guided dosing, with 68% of dosing in pediatric drug labelings being dependent on knowing either the age, body surface area, or weight of the patient to guide dosing for pediatric patients. This dependence on body size-guided dosing drives the need for special consideration when dosing a drug in overweight and obese patients. Exploratory pharmacokinetic analyses in antipsychotics illustrate possible effects of drug exposure when applying different dosing strategies for this class of drugs. Future efforts should aim to further understand the pediatric drug dosing and obesity paradigm across pediatric age ranges and drug classes to optimize drug development and clinical care for this patient population.

Physiologically Based Pharmacokinetic Modeling of Nilotinib for Drug-Drug Interactions, Pediatric Patients, and Pregnancy and Lactation

Nilotinib is a second-generation BCR-ABL tyrosine kinase inhibitor for the treatment of Philadelphia chromosome-positive chronic myeloid leukemia in both adult and pediatric patients. The pharmacokinetics (PK) of nilotinib in specific populations such as pregnant and lactating people remain poorly understood. Therefore, the objectives of the current study were to develop a physiologically based pharmacokinetic (PBPK) model to predict nilotinib PK in virtual drug-drug interaction (DDI) studies, as well as in pediatric, pregnant, and lactating populations. The nilotinib PBPK model was built in PK-Sim, which is part of the free and open-source software Open Systems Pharmacology. The observed clinical data for the validation of the nilotinib models were obtained from the literature. The model reasonably predicted nilotinib concentrations in the adult population; the DDIs between nilotinib and rifampin or ketoconazole in the adult population; and the PK in the pediatric, pregnant, and lactating populations, although in the latter 2 populations plasma concentrations were slightly underestimated. The ratio of predicted versus observed PK parameters for the adult model ranged from 0.71 to 1.11 for area under the concentration-time curve and 0.55 to 0.95 for maximum concentration. For the DDI, the predicted area under the concentration-time curve ratio and maximum concentration ratio fell within the Guest criterion. The current study demonstrated the utility of using PBPK modeling to understand the mechanistic basis of PK differences between adults and specific populations, such as pediatrics, and pregnant and lactating individuals, indicating that this technology can potentially inform or optimize dosing conditions in specific populations.

Food-Drug Effects and Pediatric Drug Development Studies Submitted to the US Food and Drug Administration, 2012-2022

Food effect (FE) studies characterize food-drug interactions that may alter the efficacy or safety of a drug, but these studies are not conducted in pediatric patients. Pediatric patients have substantial physiologic, anatomic, and dietary differences from adults, which may result in differences in their FE considerations. Therefore, the objective of this study was to identify oral drug products approved for use in pediatric patients aged <6 years with an FE observed in adults. Additional objectives were to summarize the therapeutic areas, pharmacokinetic effects, and labeling instructions that resulted from these studies. Publicly available data were searched for products studied in pediatric patients and approved for use by the United States Food and Drug Administration (FDA) from 2012 to 2022. Of the 102 oral drug products approved for use in patients aged <6 years, 43 recommended the consideration of food intake in the drug labeling. These included drug products recommended to be taken with food (n = 21, 49%) or without food (n = 14, 33%). Each of the 14 drug products recommended to be taken without food are approved for use in pediatric patients aged <2 years. The products approved for use in pediatric patients aged <2 years comprised the highest proportion with area under the plasma concentration-time curve extrapolated to infinity (AUCinf , n = 35, 75%) and maximum serum concentration (Cmax , n = 45, 80%) affected by food. Close monitoring is warranted during the postapproval period for products identified as having a significant FE in adults and that are approved for use in pediatric patients aged <6 years. Promising tools for predicting pediatric FE may include physiologically based pharmacokinetic absorption modeling.

Development of a Generic Fetal Physiologically Based Pharmacokinetic Model and Prediction of Human Maternal and Fetal Organ Concentrations of Cefuroxime

BACKGROUND AND OBJECTIVE

Physiologically based pharmacokinetic (PBPK) models for pregnant women have recently been successfully used to predict maternal and umbilical cord pharmacokinetics (PK). Because there is very limited opportunity for conducting clinical and PK investigations for fetal drug exposure, PBPK models may provide further insights. The objectives of this study were to extend a whole-body pregnancy PBPK model by multiple compartments representing fetal organs, and to predict the PK of cefuroxime in the maternal and fetal plasma, the amniotic fluid, and several fetal organs.

METHODS

To this end, a previously developed pregnancy PBPK model for cefuroxime was updated using the open-source software Open Systems Pharmacology (PK-Sim®/MoBi®). Multiple compartments were implemented to represent fetal organs including brain, heart, liver, lungs, kidneys, the gastrointestinal tract (GI), muscles, and fat tissue, as well as another compartment lumping organs and tissues not explicitly represented.

RESULTS

This novel PBPK model successfully predicted cefuroxime concentrations in maternal blood, umbilical cord, amniotic fluid, and several fetal organs including heart, liver, and lungs. Further model validation with additional clinical PK data is needed to build confidence in the model.

CONCLUSIONS

Being developed with an open-source software, the presented generic model can be freely re-used and tailored to address specific questions at hand, e.g., to assist the design of clinical studies in the context of drug research or to predict fetal organ concentrations of chemicals in the context of fetal health risk assessment.

Effect of Obesity on the Pharmacokinetics and Pharmacodynamics of Anticancer Agents

An objective of the Precision Medicine Initiative, launched in 2015 by the US Food and Drug Administration and National Institutes of Health, is to optimize and individualize dosing of drugs, especially anticancer agents, with high pharmacokinetic and pharmacodynamic variability. The American Society of Clinical Oncology recently reported that 40% of obese patients receive insufficient chemotherapy doses and exposures, which may lead to reduced efficacy, and recommended pharmacokinetic studies to guide appropriate dosing in these patients. These issues will only increase in importance as the incidence of obesity in the population increases. This publication reviews the effects of obesity on (1) tumor biology, development of cancer, and antitumor response; (2) pharmacokinetics and pharmacodynamics of small-molecule anticancer drugs; and (3) pharmacokinetics and pharmacodynamics of complex anticancer drugs, such as carrier-mediated agents and biologics. These topics are not only important from a scientific research perspective but also from a drug development and regulator perspective. Thus, it is important to evaluate the effects of obesity on the pharmacokinetics and pharmacodynamics of anticancer agents in all categories of body habitus and especially in patients who are obese and morbidly obese. As the effects of obesity on the pharmacokinetics and pharmacodynamics of anticancer agents may be highly variable across drug types, the optimal dosing metric and algorithm for difference classes of drugs may be widely different. Thus, studies are needed to evaluate current and novel metrics and methods for measuring body habitus as related to optimizing the dose and reducing pharmacokinetic and pharmacodynamic variability of anticancer agents in patients who are obese and morbidly obese.

Inclusion of Subjects who are Obese in Drug Development: Current Status and Opportunities

The prevalence of obesity has grown tremendously in recent years and this population has an increased risk of disease comorbidities. The presence of disease comorbidities requires treatment interventions and proper dosing guidelines. However, drug development programs often do not have adequate representation of individuals who are obese in clinical trials, leaving gaps in the understanding of treatment response leading to a lack of adequate individualization options. Based on a recent survey of approved drug product package inserts, very few approved products included specific dosing based on obesity, in both adults and pediatrics. Reasons for the limited information on patients who are obese may include the under-reporting of information regarding such patients and a lack of clinical trial diversity in enrolling patient groups in whom obesity or obesity-related comorbidities are more prevalent. An inadvertent impact of the practice of exclusion of subsets of patients with some comorbidities in clinical trials may play a role in the reduced enrollment of individuals who are obese. Recently, regulatory authorities have taken specific initiatives to promote clinical trial diversity, including engaging with stakeholders and publishing regulatory guidance. These guidance documents highlight the need to enroll diverse clinical trial populations and provide recommendations on concepts related to drug development for obese populations. Such efforts will help to address the gap in information regarding drug response and dosing in patients who are obese.

Obesity Considerations in Pediatric Drug Development, 2016-2021

Pediatric obesity is a global public health concern. Obesity-related physiological changes may affect the pharmacokinetics of drugs and lead to therapeutic failure or toxicities. An earlier review of pediatric drug development programs from 2007 to 2016 found that, of 89 programs listing obesity-related terms, only 4 (4%) products described pharmacokinetic changes associated with obesity. This review examined obesity considerations for 185 drug products for which pediatric drug development programs were submitted to the US Food and Drug Administration (FDA) between 2016 and 2021. The FDA-authored review documents and drug product labeling were queried for obesity-related terms and the review found 97/185 (52%) drug products had obesity-related terms in these sources. Of the 97 drug products, 55/97 (57%) had obesity-related terms in the FDA-authored reviews only, 13/97 (13%) had obesity-related terms in the drug product labeling only, and 29/97 (30%) had obesity-related terms in both FDA-authored reviews and drug product labeling. Most of the obesity-related information in the drug product labeling originated from data collected from adults. Only 13/185 (7%) drug product labeling contained obesity-related terms in reference to drug pharmacokinetics. Specific dosage recommendations for the use of the drug products in pediatric patients who are obese remain lacking. The dearth of available information to guide drug dosages in the obese pediatric population suggests that further research, innovative approaches, and evidence-based guidelines are needed to inform the optimal therapeutic use of drugs in this population.

Pediatric dosing for locally acting drugs in submissions to the U.S. Food and Drug Administration between 2002 and 2020

Deriving pediatric doses for locally acting drugs (LADs) presents a unique challenge because limited systemic exposure hinders commonly used approaches such as pharmacokinetic matching to adults. This study systematically evaluated drug development practices used for pediatric dose selection of LADs approved by the U.S. Food and Drug Administration from 2002 to 2020. The three study objectives were: (1) to determine the dose selection approach for the labeled pediatric dose, (2) to examine the studied pediatric dose(s), and (3) to evaluate the characteristics of the pediatric clinical programs used to support the labeled pediatric dose. A total of 187 pediatric submissions were characterized for the labeled and studied pediatric doses of LADs. The pediatric dose was predominantly labeled as a flat dose (91%) and at a single-dose level (67%) similar to adults. The majority (68.4%) of the submissions had the same labeled dose for pediatrics and adults. Independent pharmacodynamic/efficacy studies in pediatric patients commonly (64.2%) provided supportive evidence for the labeled pediatric dose. Inhalation, nasal, and injectable submissions had the highest number of clinical trials, lowest usage of an extrapolation of efficacy approach, and utilized diverse approaches in selecting the studied pediatric doses. This article highlights approaches for LAD dosing in pediatric patients and can be used to inform drug development of these products in the pediatric population.

Need for Representation of Pediatric Patients with Obesity in Clinical Trials

Clinical trials are an integral aspect of drug development. Tremendous progress has been made in ensuring drug products are effective and safe for use in the intended pediatric population, but there remains a paucity of information to guide drug dosages in pediatric patients with obesity. This is concerning because obesity may influence the disposition of drug products. When pediatric patients with obesity are not enrolled in clinical trials, dosing options for use in this subpopulation may be suboptimal. Reliance on physiological-based dosing strategies that are not informed by evaluation of the pharmacokinetics of the drug product could lead to under- or over-dosing with ensuing therapeutic failure or toxicity consequences. Thus, representation of pediatric patients with obesity in clinical trials is crucial to understand the benefit-risk profile of drug products in this subpopulation. It is important to acknowledge that this is a challenging endeavor, but not one that is insurmountable. Collective efforts from multiple stakeholders including drug developers and regulators to enhance diversity in clinical trials can help fill critical gaps in knowledge related to the influence of obesity on drug disposition.

Assessing Information Gaps Associated with Initial Pediatric Study Plans for New Oncology Drug and Biological Products

The Research Acceleration for Cure and Equity (RACE) for Children Act requires sponsors to submit a Pediatric Study Plan (PSP) with a proposed pediatric investigation of new molecularly targeted drugs and biologics that are intended for treatment of adult cancers, and whose target is relevant to pediatric cancer or provide a justification for a plan to request a deferral or waiver of the required investigation. A landscape analysis was performed to identify trends in information gaps associated with a sponsor's first initial PSP (iPSP) submission for oncologic new molecular entities received in 2021. Comments sent to sponsors by the US Food and Drug Administration (FDA) during the review process of each evaluated iPSP were categorized using nine flags relating to different portions of the PSP. For iPSPs that included a plan for a full waiver request, the most common information gap was inadequate justification based on molecular target relevance. All other sponsor proposed plans (deferral and/or partial waiver or investigation) were found to have information gaps related to clinical study features, clinical pharmacology, and/or missing clinical or nonclinical data. This landscape analysis of iPSPs shows the trends in comments that often occur during initial review and may help to provide sponsors with more direction for preparing an adequate iPSP to fulfill statutory requirements aimed at ensuring pediatric patients are considered in the development of new molecularly targeted drugs.

Integration of Biorelevant Pediatric Dissolution Methodology into PBPK Modeling to Predict In Vivo Performance and Bioequivalence of Generic Drugs in Pediatric Populations: a Carbamazepine Case Study

This study investigated the impact of gastro-intestinal fluid volume and bile salt (BS) concentration on the dissolution of carbamazepine (CBZ) immediate release (IR) 100 mg tablets and to integrate these in vitro biorelevant dissolution profiles into physiologically based pharmacokinetic modelling (PBPK) in pediatric and adult populations to determine the biopredictive dissolution profile. Dissolution profiles of CBZ IR tablets (100 mg) were generated in 50-900 mL biorelevant adult fasted state simulated gastric and intestinal fluid (Ad-FaSSGF and Ad-FaSSIF), also in three alternative compositions of biorelevant pediatric FaSSGF and FaSSIF medias at 200 mL. This study found that CBZ dissolution was poorly sensitive to changes in the composition of the biorelevant media, where dissimilar dissolution (F2 = 46.2) was only observed when the BS concentration was changed from 3000 to 89 μM (Ad-FaSSIF vs Ped-FaSSIF 50% 14 BS). PBPK modeling demonstrated the most predictive dissolution volume and media composition to forecast the PK was 500 mL of Ad-FaSSGF/Ad-FaSSIF media for adults and 200 mL Ped-FaSSGF/FaSSIF media for pediatrics. A virtual bioequivalence simulation was conducted by using Ad-FaSSGF and/or Ad-FaSSIF 500 mL or Ped-FaSSGF and/or Ped-FaSSIF 200 mL dissolution data for CBZ 100 mg (reference and generic test) IR product. The CBZ PBPK models showed bioequivalence of the product. This study demonstrates that the integration of biorelevant dissolution data can predict the PK profile of a poorly soluble drug in both populations. Further work using more pediatric drug products is needed to verify biorelevant dissolution data to predict the in vivo performance in pediatrics.

Pediatric Efficacy Extrapolation in Drug Development Submitted to the US Food and Drug Administration 2015-2020

Pediatric extrapolation plays a key role in the availability of reliable pediatric use information in approved drug labeling. This review examined the use of pediatric extrapolation in studies submitted to the US Food and Drug Administration and assessed changes in extrapolation approaches over time. Pediatric studies of 125 drugs submitted to the US Food and Drug Administration that led to subsequent pediatric information in drug labeling between 2015 and 2020 were reviewed. The use of pediatric extrapolation for each drug was identified and categorized as "complete," "partial," or "no" extrapolation. Approaches to pediatric extrapolation of efficacy changed over time. Complete extrapolation of efficacy was the predominantly used approach. "Complete," "partial," or "no" extrapolation was used for 51%, 23%, and 26% of the drugs, respectively. This represents a shift in extrapolation approaches when compared to a previous study that evaluated pediatrics drug applications between 2009 and 2014, which found complete, partial, or no extrapolation was used for 34%, 29%, and 37% of the drugs, respectively. Pediatric extrapolation approaches may continue to shift as emerging science fills gap in knowledge of the fundamental assumptions underlying this scientific tool. The international community continues to collaborate on discussions of pediatric extrapolation of efficacy from adults and other pediatric subpopulations to optimize its use for pediatric drug development.

Extrapolation of Adult Efficacy Data to Pediatric Systemic Lupus Erythematosus: Evaluating Similarities in Exposure-Response

To streamline drug development, the United States Food and Drug Administration (FDA) can consider the extrapolation of adult efficacy data to children when the disease and drug effects are sufficiently similar. This study explored whether the relationship between drug exposure and response for selected drugs in systemic lupus erythematosus (SLE) was sufficiently similar to support a consideration of the extrapolation of adult efficacy data to children of ≥5 years of age. An exposure-response analysis of drugs used to treat SLE was conducted using published exposure versus response and efficacy versus time data. Statistical analyses included noncompartmental analysis of a drug's area under the effect curve and direct Imax pharmacodynamic (PD) modeling. Six drugs were included: azathioprine, belimumab, cyclophosphamide, hydroxychloroquine, mycophenolate/mycophenolic acid, and rituximab. For belimumab, the net change in responders at week 52 (the primary end point) was nearly identical between 1 adult trial and the pediatric trial. For mycophenolate, PD modeling suggested no significant differences in exposure and SLE disease activity between adults and children. For azathioprine, cyclophosphamide, hydroxychloroquine, and rituximab the data were not sufficient to quantitatively characterize the exposure-response relationship, but the clinical or pharmacologic response between children and adults was similar overall. Adult SLE data should be leveraged to guide pediatric drug development programs and identify areas with residual uncertainty regarding the effectiveness or safety of a drug in children. The degree to which efficacy extrapolation can reduce clinical trial requirements in pediatric SLE should be individualized for each new drug product, depending in part on the mechanism of action of the drug and the similarity of disease manifestations in children and adults.

Fine-Tuning the Relevance of Molecular Targets to Pediatric Cancer: Addressing Additional Layers of Complexity

The Research to Accelerate Cures and Equity (RACE) for Children Act requires an assessment of molecular targets relevant to pediatric cancer. Due to the biological complexity, candidate molecular targets have been primarily evaluated based on single features such as the presence of mutations or deregulated expression. As the understanding of tumor biology evolves, the relevance of certain molecular targets may need to be assessed at isoform and/or mutation variant level to optimize tailored therapeutic interventions.

A Tribute to the Pioneers of Fetal Pharmacology

Clinical pharmacology is a branch of the field of pharmacology that evolved following the recognition that the nature, duration, and intensity of drug action depend on both the intrinsic properties of the drug and an interaction with the host to whom the drug is given. Advances in drug development have placed highly specific and extremely potent therapeutic agents in the marketplace. While these advances have progressed rapidly in adult medicine, pediatric clinical pharmacology has not kept pace and until very recently has lagged behind the research and attention paid to the proper use of therapeutic and diagnostic drugs in adults. Recognition that advances in the science of developmental pharmacology and pediatric clinical pharmacology were essential in the development of new drugs to treat children came in the 1950s and 1960s mostly through the work of 2 pioneering scientists in fetal and perinatal clinical pharmacology, Drs Sumner Yaffe and Bernard Mirkin. Here we pay a tribute to these most influential pioneers in the United States who were instrumental in paving the path for advancing the field of fetal and perinatal pharmacology concepts and their incorporation into pediatric drug development programs.

Pediatric and Adult Placebo Response Rates in Placebo-Controlled Clinical Trials Submitted to the US FDA 2012-2020

The use of placebo concurrent control (placebo-controlled) is the most rigorous method of evaluating the safety and efficacy of investigational treatments. However, the use of a placebo group in pediatric product development can be challenging due to ethical considerations and potential differences in placebo response rates between adults and children. This study reports the US Food and Drug Administration's experience with placebo response rates in the pediatric population. Products studied under the Best Pharmaceuticals for Children Act and the Pediatric Research Equity Act between 2012 and 2020 were screened. Study characteristics including study type, primary efficacy endpoint(s), placebo response rates for the primary efficacy endpoint(s) and studied age range were collected. A total of 71 drug products used a placebo-controlled trial. Of these, thirteen products had an identical study design and trial characteristics including the primary efficacy endpoints between pediatric and adult studies. Fifteen products were studied in trials with identical study design but only different primary efficacy endpoints in pediatric and adult populations. Ten products had combined adolescent and adult trials with separate pediatric trials in younger age groups. In each of these cases, the pediatric placebo response was greater, for some trials, and less, for other trials, than the adult placebo response. The pediatric placebo response can vary within an age group for a drug product. Future studies should examine the factors leading to a similarity or dissimilarity in placebo response between pediatric patients and adults. This article is protected by copyright. All rights reserved.

Mechanistic Modeling of Placental Drug Transfer in Humans: How Do Differences in Maternal/Fetal Fraction of Unbound Drug and Placental Influx/Efflux Transfer Rates Affect Fetal Pharmacokinetics?

Background: While physiologically based pharmacokinetic (PBPK) models generally predict pharmacokinetics in pregnant women successfully, the confidence in predicting fetal pharmacokinetics is limited because many parameters affecting placental drug transfer have not been mechanistically accounted for. Objectives: The objectives of this study were to implement different maternal and fetal unbound drug fractions in a PBPK framework; to predict fetal pharmacokinetics of eight drugs in the third trimester; and to quantitatively investigate how alterations in various model parameters affect predicted fetal pharmacokinetics. Methods: The ordinary differential equations of previously developed pregnancy PBPK models for eight drugs (acyclovir, cefuroxime, diazepam, dolutegravir, emtricitabine, metronidazole, ondansetron, and raltegravir) were amended to account for different unbound drug fractions in mother and fetus. Local sensitivity analyses were conducted for various parameters relevant to placental drug transfer, including influx/efflux transfer clearances across the apical and basolateral membrane of the trophoblasts. Results: For the highly-protein bound drugs diazepam, dolutegravir and ondansetron, the lower fraction unbound in the fetus vs. mother affected predicted pharmacokinetics in the umbilical vein by ≥10%. Metronidazole displayed blood flow-limited distribution across the placenta. For all drugs, umbilical vein concentrations were highly sensitive to changes in the apical influx/efflux transfer clearance ratio. Additionally, transfer clearance across the basolateral membrane was a critical parameter for cefuroxime and ondansetron. Conclusion: In healthy pregnancies, differential protein binding characteristics in mother and fetus give rise to minor differences in maternal-fetal drug exposure. Further studies are needed to differentiate passive and active transfer processes across the apical and basolateral trophoblast membrane.

Pediatric Drug Development Studies for Familial Hypercholesterolemia Submitted to the US Food and Drug Administration Between 2007 and 2020

Familial hypercholesterolemia (FH) is an autosomal dominant genetic disorder of lipoprotein metabolism that leads to an increased risk of developing atherosclerosis and coronary artery disease. Hypercholesterolemia in pediatric patients is typically due to FH. Treatment of pediatric FH is achieved through lifestyle modifications, lipid-modifying pharmacotherapy, and/or apheresis. The primary objective of this review is to describe the characteristics of clinical trials conducted in pediatric patients with FH with data submitted to the US Food and Drug Administration from 2007 to 2020. Of 10 trials with 8 products in pediatric FH submitted to the Food and Drug Administration, 1 product was studied in both the heterozygous and the homozygous phenotypes, 5 were studied for heterozygous hypercholesterolemia only, and 2 were studied for homozygous familial hypercholesterolemia only. Most of the trials included pediatric patients ≥10 years of age and older. Clinical trial characteristics including the primary efficacy end points between pediatric and adult trials were mostly identical. Many lipid-lowering drugs with novel mechanisms of action have been recently approved or are currently being studied. In summary, the drug treatment of hypercholesterolemia in pediatric patients is expanding beyond the use of statins, and now involves multiple mechanisms of action involving cholesterol metabolism. As younger pediatric patients are diagnosed and treated for heterozygous familial hypercholesterolemia and homozygous familial hypercholesterolemia, optimizing the doses of these agents and safety studies specific to younger pediatric patients will be necessary.

Fusion Oncoproteins in Childhood Cancers: Potential Role in Targeted Therapy

Cancer remains the leading cause of death from disease in children. Historically, in contrast to their adult counterparts, the causes of pediatric malignancies have remained largely unknown, with most pediatric cancers displaying low mutational burdens. Research related to molecular genetics in pediatric cancers is advancing our understanding of potential drivers of tumorigenesis and opening new opportunities for targeted therapies. One such area is fusion oncoproteins, which are a product of chromosomal rearrangements resulting in the fusion of different genes. They have been identified as oncogenic drivers in several sarcomas and leukemias. Continued advancement in the understanding of the biology of fusion oncoproteins will contribute to the discovery and development of new therapies for childhood cancers. Here we review the current scientific knowledge on fusion oncoproteins, focusing on pediatric sarcomas and hematologic cancers, and highlight the challenges and current efforts in developing drugs to target fusion oncoproteins.

Drug Safety in Labeling for Pediatric Drug Development and Dose Selection in Submissions to the US Food and Drug Administration

Pediatric safety evaluations are an essential part of a pediatric drug development program. Communication of the results of these safety evaluations is primarily accomplished by labeling of the drug either during the initial pediatric drug development program, or during the postmarketing period after drug approval for pediatric patients. During drug development, the dose-adverse drug event (ADE) relationship is an important part of the evaluation, but a consideration for pediatric ADEs that are unrelated to drug dosage must be maintained. Examples of dose-related and non-dose-related ADEs are presented. The failure to label a product for pediatric use has been safety related for a number of development programs. The US Food and Drug Administration's Pediatric Advisory Committee is a primary source of the pediatric postmarketing safety review and has been associated with a number of labeling changes through its ongoing review process. Pediatric drug safety remains a critical part of the assessment of dose-effect relationship in the pediatric patient population during the drug development and postmarketing surveillance process.

Methods Used for Pediatric Dose Selection in Drug Development Programs Submitted to the US FDA 2012-2020

Dosing is a critical aspect of drug development in pediatrics that has led to trial failures and the inability to label the drug for pediatric use by the US Food and Drug Administration. Developing a structured approach for pediatric dose selection requires knowledge of the current approaches and their success or failure. This study describes the current experience with pediatric dosing methods from 2012 to 2020 and had 2 primary objectives: (1) to identify how the initial pediatric dose was selected and (2) to identify the pivotal dosing strategy used to identify the initially selected dose for safety and efficacy for pediatric clinical trials. Through September 2020, a total of 275 pediatric drug development programs were characterized for initial and pivotal dosing strategies. The success rate for labeling for pediatric use was 76.4%. The most common initial dosing strategy was previous experience with the product, followed by allometric scaling and exposure matching with adults. The most common pivotal dosing strategy was titration to target response in 33% of programs, with the second and third most common being pharmacokinetic/pharmacodynamic studies (30%) and exposure matching (20%), respectively. Additionally, about one-half of pediatric programs incorporated model-informed drug development. The emergence of titration to target response may signal a shift toward precision medicine in pediatric patients. Future work in pediatric drug dose selection should move toward the development of a structured pediatric dose selection approach.

Applying the Noninferiority Paradigm to Assess Exposure-Response Similarity and Dose Between Pediatric and Adult Patients

The use of extrapolation of efficacy in pediatric drug development programs is possible when disease progression and treatment response are similar in adult and pediatric populations. Historically, the exposure-response (E-R) similarity was assessed by visual inspection of 2 E-R curves to support pediatric extrapolation. The aim of this study was to develop a quantitative framework to describe the E-R relationship and the difference in E-R between pediatric and adult patients based on accumulated experience in pediatric drug development programs. Using clinical data for 8 drugs with either a linear or nonlinear E-R relationship, we adapted the methodology used in noninferiority testing to assess the E-R similarity between adult and pediatric patients at the targeted drug exposure. We implemented bootstrap-based and Bayesian-based methodologies to estimate the probability of concluding noninferiority of the E-R relationship. This approach provides objective criteria that can be applied to an assessment of E-R noninferiority in 2 populations to support extrapolation of efficacy in drug development programs from adults to pediatric populations.

Progress in Drug Development-Pediatric Dose Selection: Workshop Summary

The "Pediatric Dose Selection" workshop was held in October 2020 and sponsored by the U.S. Food and Drug Administration and the University of Maryland Center for Excellence in Regulatory Science and Innovation. A summary of the presentations in the context of pediatric drug development is summarized in this article.

Evaluation of Physiologically Based Pharmacokinetic Models to Predict the Absorption of BCS Class I Drugs in Different Pediatric Age Groups

Age-related changes in many parameters affecting drug absorption remain poorly characterized. The objective of this study was to apply physiologically based pharmacokinetic (PBPK) models in pediatric patients to investigate the absorption and pharmacokinetics of 4 drugs belonging to the Biopharmaceutics Classification System (BCS) class I administered as oral liquid formulations. Pediatric PBPK models built with PK-Sim/MoBi were used to predict the pharmacokinetics of acetaminophen, emtricitabine, theophylline, and zolpidem in different pediatric populations. The model performance for predicting drug absorption and pharmacokinetics was assessed by comparing the predicted absorption profile with the deconvoluted dose fraction absorbed over time and predicted with observed plasma concentration-time profiles. Sensitivity analyses were performed to analyze the effects of changes in relevant input parameters on the model output. Overall, most pharmacokinetic parameters were predicted within a 2-fold error range. The absorption profiles were generally reasonably predicted, but relatively large differences were observed for acetaminophen. Sensitivity analyses showed that the predicted absorption profile was most sensitive to changes in the gastric emptying time (GET) and the specific intestinal permeability. The drug's solubility played only a minor role. These findings confirm that gastric emptying time, more than intestinal permeability or solubility, is a key factor affecting BCS class I drug absorption in children. As gastric emptying time is prolonged in the fed state, a better understanding of the interplay between food intake and gastric emptying time in children is needed, especially in the very young in whom the (semi)fed condition is the prevailing prandial state, and hence prolonged gastric emptying time seems more plausible than the fasting state.

Inclusion of Infants and Neonates in Pediatric Orphan Product Approvals

The Orphan Drug Act (ODA) of 1983 was enacted to provide financial incentives to drug sponsors to develop therapies for rare diseases. Although this act increased the number of orphan products approved, there are still a limited number of products available for the pediatric population because orphan drug products are exempt from the Pediatric Research Equity Act. The objectives of this study were (i) to evaluate the pediatric orphan drug studies submitted to the US Food and Drug Administration (FDA) in the period of 2007-2018 and (ii) to examine whether orphan drug products were fully labeled with a pediatric indication in infants and neonates. Out of the 468 indications evaluated, 171 (37%) were FDA-labeled for use in the pediatric population. Labeling for the 12 to < 18 years age group was most common (98%). Fifty-two percent of FDA-labeled pediatric indications included the newborn to < 2 years of age group. In this newborn to < 2 years age group, the indication was labeled without pivotal clinical trials in 43% of the programs. Of the 60 new indications not labeled down to birth, 50% were found to have an age of onset and diagnosis that occurs earlier than the age approved for use of the product for that indication. In summary, although the ODA has been successful in improving pediatric access to medications for rare diseases, our analysis identified the incomplete labeling for pediatric patients under 2 years of age. Strategies to include the birth to < 2 years old group of pediatric patients in orphan drug development programs should be explored.

Development of a Pediatric Relative Bioavailability/Bioequivalence Database and Identification of Putative Risk Factors Associated With Evaluation of Pediatric Oral Products

Generally, bioequivalence (BE) studies of drug products for pediatric patients are conducted in adults due to ethical reasons. Given the lack of direct BE assessment in pediatric populations, the aim of this work is to develop a database of BE and relative bioavailability (relative BA) studies conducted in pediatric populations and to enable the identification of risk factors associated with certain drug substances or products that may lead to failed BE or different pharmacokinetic (PK) parameters in relative BA studies in pediatrics. A literature search from 1965 to 2020 was conducted in PubMed, Cochrane Library, and Google Scholar to identify BE studies conducted in pediatric populations and relative BA studies conducted in pediatric populations. Overall, 79 studies covering 37 active pharmaceutical ingredients (APIs) were included in the database: 4 bioequivalence studies with data that passed BE evaluations; 2 studies showed bioinequivalence results; 34 relative BA studies showing comparable PK parameters, and 39 relative BA studies showing differences in PK parameters between test and reference products. Based on the above studies, common putative risk factors associated with differences in relative bioavailability (DRBA) in pediatric populations include age-related absorption effects, high inter-individual variability, and poor study design. A database containing 79 clinical studies on BE or relative BA in pediatrics has been developed. Putative risk factors associated with DRBA in pediatric populations are summarized.

Physiologically Based Pharmacokinetic Modeling Framework to Predict Neonatal Pharmacokinetics of Transplacentally Acquired Emtricitabine, Dolutegravir, and Raltegravir

BACKGROUND AND OBJECTIVE

Little is understood about neonatal pharmacokinetics immediately after delivery and during the first days of life following intrauterine exposure to maternal medications. Our objective was to develop and evaluate a novel, physiologically based pharmacokinetic modeling workflow for predicting perinatal and postnatal disposition of commonly used antiretroviral drugs administered prenatally to pregnant women living with human immunodeficiency virus.

METHODS

Using previously published, maternal-fetal, physiologically based pharmacokinetic models for emtricitabine, dolutegravir, and raltegravir built with PK-Sim/MoBi^®, placental drug transfer was predicted in late pregnancy. The total drug amount in fetal compartments at term delivery was estimated and subsequently integrated as initial conditions in different tissues of a whole-body, neonatal, physiologically based pharmacokinetic model to predict drug concentrations in the neonatal elimination phase after birth. Neonatal elimination processes were parameterized according to published data. Model performance was assessed by clinical data.

RESULTS

Neonatal physiologically based pharmacokinetic models generally captured the initial plasma concentrations after delivery but underestimated concentrations in the terminal phase. The mean percentage error for predicted plasma concentrations was - 71.5%, - 33.8%, and 76.7% for emtricitabine, dolutegravir, and raltegravir, respectively. A sensitivity analysis suggested that the activity of organic cation transporter 2 and uridine diphosphate glucuronosyltransferase 1A1 during the first postnatal days in term newborns is ~11% and ~30% of that in adults, respectively.

CONCLUSIONS

These findings demonstrate the general feasibility of applying physiologically based pharmacokinetic models to predict washout concentrations of transplacentally acquired drugs in newborns. These models can increase the understanding of pharmacokinetics during the first postnatal days and allow the prediction of drug exposure in this vulnerable population.

Evaluating Patients With Impaired Renal Function During Drug Development: Highlights From the 2019 US FDA Pharmaceutical Science and Clinical Pharmacology Advisory Committee Meeting

Patients with multiple chronic conditions, including more advanced chronic kidney disease (CKD), are often excluded from clinical trials, creating challenges in deriving appropriate dosing information and labeling. This article summarizes the May 7, 2019, US Food and Drug Administration Pharmaceutical Science and Clinical Pharmacology Advisory Committee Meeting, which solicited expert opinions on how to enroll patients with more advanced CKD into clinical trials as well as the assumptions behind and different approaches of exposure-matching.

Regulatory Considerations for the Mother, Fetus and Neonate in Fetal Pharmacology Modeling

The regulatory framework for considering the fetal effects of new drugs is limited. This is partially due to the fact that pediatric regulations (21 CFR subpart D) do not apply to the fetus, and only US Health and Human Service (HHS) regulations apply to the fetus. The HHS regulation 45 CFR Part 46 Subpart B limits research approvable by an institutional review board to research where the risk to the fetus is minimal unless the research holds out the prospect of a direct benefit to the fetus or the pregnant woman (45 CFR 46.204). Research that does not meet these requirements, but presents an opportunity to understand, prevent, or alleviate a serious problem affecting the health of pregnant women, fetuses, or neonates, may be permitted by the Secretary of the HHS after expert panel consultation and opportunity for public review and comment (45 CFR 46.407). If the product is regulated by the US Food and Drug Administration (FDA), FDA may get involved in the review process. The FDA does however have a Reviewer Guidance on Evaluating the Risks of Drug Exposure in Human Pregnancies from 2005 and this guidance does discuss the intensity of drug exposure. Estimation of that exposure using physiologically based pharmacokinetic (PBPK) modeling has been suggested by some investigators. Given that drug exposure during pregnancy will impact the fetus, a number of new guidances in the last 2 years also address inclusion of pregnant women in clinical drug trials. Therefore, the drug-specific information on fetal pharmacology will increase dramatically in the next decade due to interest in drugs administered in pregnancy and with the assistance of model-informed drug development.

Dosing Recommendations for Pediatric Patients With Renal Impairment

A treatment gap exists for pediatric patients with renal impairment. Alterations in renal clearance and metabolism of drugs render standard dosage regimens inappropriate and may lead to drug toxicity, but these studies are not routinely conducted during drug development. The objective of this study was to examine the clinical evidence behind current renal impairment dosage recommendations for pediatric patients in a standard pediatric dosing handbook. The sources of recommendations and comparisons included the pediatric dosing handbook (Lexicomp), the U.S. Food and Drug Administration-approved manufacturer's labels, and published studies in the literature. One hundred twenty-six drugs in Lexicomp had pediatric renal dosing recommendations. Only 14% (18 of 126) of Lexicomp pediatric renal dosing recommendations referenced a pediatric clinical study, and 15% of manufacturer's labels (19 of 126) described specific dosing regimens for renally impaired pediatric patients. Forty-two products had published information on pediatric renal dosing, but 19 (45%) were case studies. When pediatric clinical studies were not referenced in Lexicomp, the renal dosing recommendations followed the adult and pediatric dosing recommendations on the manufacturer's label. Clinical evidence in pediatric patients does not exist for most renal dosing recommendations in a widely used pediatric dosing handbook, and the adult renal dosing recommendations from the manufacturer's label are currently the primary source of pediatric renal dosing information.

Incorporating Ontogeny in Physiologically Based Pharmacokinetic Modeling to Improve Pediatric Drug Development: What We Know About Developmental Changes in Membrane Transporters

Developmental changes in the biological processes involved in the disposition of drugs, such as membrane transporter expression and activity, may alter the drug exposure and clearance in pediatric patients. Physiologically based pharmacokinetic (PBPK) models take these age-dependent changes into account and may be used to predict drug exposure in children. As a result, this mechanistic-based tool has increasingly been applied to improve pediatric drug development. Under the Prescription Drug User Fee Act VI, the US Food and Drug Administration has committed to facilitate the advancement of PBPK modeling in the drug application review process. Yet, significant knowledge gaps on developmental biology still exist, which must be addressed to increase the confidence of prediction. Recently, more data on ontogeny of transporters have emerged and supplied a missing piece of the puzzle. This article highlights the recent findings on the ontogeny of transporters specifically in the intestine, liver, and kidney. It also provides a case study that illustrates the utility of incorporating this information in predicting drug exposure in children using a PBPK approach. Collaborative work has greatly improved the understanding of the interplay between developmental physiology and drug disposition. Such efforts will continue to be needed to address the remaining knowledge gaps to enhance the application of PBPK modeling in drug development for children.

Pediatric Renal Ontogeny and Applications in Drug Development

The clinical applications of renal ontogeny mainly include renal function evaluation and optimal dosing of renally eliminated drugs in pediatric patients, which rely on pharmacometric models and/or bedside estimated glomerular filtration rate equations. However, these applications in drug development are based on an understanding of renal function development, especially when considering premature infants, and the renal biomarkers that can be used for renal function assessment. This review provides a general overview on (1) renal function development, (2) the biomarkers that are used to assess renal function, and (3) the practical application of this knowledge to drug dosing for renally eliminated drugs during pediatric development. While pharmacometric approaches for estimating renal function during development have improved considerably, the number of drug development programs that have studied premature infants is small and suggests that caution should be taken in estimating doses for renally eliminated drugs during periods of rapid change in renal function.

The Revolution in Pediatric Drug Development and Drug Use: Therapeutic Orphans No More

This lecture was given by Dr. Burckart in association with presentation of the 2014 Sumner J. Yaffe Lifetime Achievement Award in Pediatric Pharmacology and Therapeutics, which is selected by the Pediatric Pharmacy Association. Multiple factors make conducting drug studies in the pediatric population difficult, resulting in a historic lack of information surrounding safe and efficacious drug dosing in children. The paradigm in pediatric drug development has shifted from normal science being that children are therapeutic orphans in the drug development system, to a model drift caused by pediatric legislation, to a model crisis caused by failed pediatric drug development trials, to finally a model revolution that includes pediatric patients routinely in drug development. Major regulatory actions and the accumulation of scientific evidence has created an environment where clinicians can expect properly labeled drug usage information for the pediatric population.

Creatinine-Based Renal Function Assessment in Pediatric Drug Development: An Analysis Using Clinical Data for Renally Eliminated Drugs

The estimated glomerular filtration rate (eGFR) equations based on serum creatinine (SCR) have been used for pediatric dose adjustment in drug labeling. This study evaluated the performance of those equations in estimating individual clearance of drugs that are predominantly eliminated by glomerular filtration, using clinical data from the renally eliminated drugs gadobutrol, gadoterate, amikacin, and vancomycin. The eGFR was compared with the observed drug clearance (CL) in 352 pediatric patients from birth to 12 years of age. Multiple eGFR equations overestimated the drug CL on average, including the original and bedside Schwartz equations, which showed an average eGFR/CL ratio between 1 and 3. Further analysis with bedside Schwartz equation showed a higher eGFR/CL ratio in the subjects with a lower SCR or CL. Supraphysiological eGFR as high as 380 mL/min/1.73 m² was obtained using the bedside Schwartz equation for some of the subjects, most of whom are children < 2 years of age with SCR < 0.2 mg/dL. Excluding the subjects with supraphysiological eGFR from the analysis did not change the overall trend of overestimation. In conclusion, Schwartz equations led to an overestimation of drug clearance for the drugs evaluated. When greater precision is required in predicting eGFR for pediatric patients, such as in drug dosing, revised k constants for the Schwartz equation or new methods of glomerular filtration rate estimation may be necessary.

Prediction of Maternal and Fetal Pharmacokinetics of Dolutegravir and Raltegravir Using Physiologically Based Pharmacokinetic Modeling

BACKGROUND

Predicting drug pharmacokinetics in pregnant women including placental drug transfer remains challenging. This study aimed to develop and evaluate maternal-fetal physiologically based pharmacokinetic models for two antiretroviral drugs, dolutegravir and raltegravir.

Combined Pediatric and Adult Trials Submitted to the US Food and Drug Administration 2012-2018

Despite legislation incentivizing and requiring drug companies to conduct pediatric clinical trials, there still is a 9-year delay in drug approval for pediatric labeling after the initial adult drug approval. The aim of this study was to review the experience of the US Food and Drug Administration (FDA) with combined pediatric and adult trials as a means for expediting pediatric approval and labeling. Combined pediatric and adult trials submitted to the FDA from 2012 to 2018 were reviewed. Only the publicly available labels and reviews were utilized for this analysis. Combined trials were identified for 72 products, with a total of 156 combined adult and pediatric trials. The therapeutic areas with the largest number of combined trials were in pulmonology for products reviewed under the Best Pharmaceuticals for Children Act (BPCA) and/or the Pediatric Research Equity Act (PREA), and hematology reviewed under the Orphan Drug Act (ODA). All drugs that utilized combined pediatric and adult clinical trials were approved simultaneously for both the adults and that part of the pediatric population. A separate pediatric subgroup efficacy analysis was reported in 57% and 48% of products under BPCA/PREA and the ODA, respectively, with a separate safety analysis in 48% and 38% of these products. When considering both BPCA/PREA and orphan drug studies, all the combined pediatric and adult trials allowed concurrent approval and labeling for part of the pediatric population at the time of the adult approval.

Exposure-Response Assessment in Pediatric Drug Development Studies Submitted to the US Food and Drug Administration

Exposure-response (E-R) modeling provides a quantitative tool to leverage adult data to support pediatric trial design and drug approval. The pediatric E-R studies submitted to US Food and Drug Administration (FDA) between 2007 and 2018 were surveyed in the context of various types of trial designs supporting drug approval in the pediatric population. The applications of E-R evaluation in pediatric drug development programs are mainly focused on three areas: (i) supporting pediatric extrapolation when the E-R relationships are similar between the pediatric and adult populations; (ii) dose selection to balance the risk-benefit profile based on the change in efficacy and safety response with different exposure levels; and (iii) approval of a new formulation, new dosing regimen, or new route of administration, where E-R evaluation helps quantify the change in clinical response between the old and new strategies. E-R modeling will continue to play an expanded role in pediatric drug development in the future.

International Coherence of Pediatric Drug Labeling for Drug Safety: Comparison of Approved Labels in Korea and the United States

The objective of this study was to analyze information on pediatric use in Korean drug product labels and compare it with that in US Food and Drug Administration (FDA) labeling information. Prescription information on pediatric use contained in the commonly used drugs’ product labels approved by Korean government was compared with that approved by the FDA. Among the top 50 commonly prescribed drugs, 20 drugs were deemed to have insufficient prescribing information in Korean drug labels. Pediatric prescribing information regarding indication, approved age, formulations, and safety was insufficient in Korean drug labels compared with those in the FDA. Most important, the adverse events frequently reported in Korean children were not sufficiently presented in drug labels. In conclusion, this study highlights the urgent need for the Korean regulatory agency to encourage and accelerate research and development to increase the extent of pediatric prescribing information to be added to drug labels to promote appropriate drug prescribing for children.

Physiologically Based Pharmacokinetic Models to Predict Maternal Pharmacokinetics and Fetal Exposure to Emtricitabine and Acyclovir

Pregnancy is associated with physiological changes that may impact drug pharmacokinetics (PK). The goals of this study were to build maternal-fetal physiologically based pharmacokinetic (PBPK) models for acyclovir and emtricitabine, 2 anti(retro)viral drugs with active renal net secretion, and to (1) evaluate the predicted maternal PK at different stages of pregnancy; (2) predict the changes in PK target parameters following the current dosing regimen of these drugs throughout pregnancy; (3) evaluate the predicted concentrations of these drugs in the umbilical vein at delivery; (4) compare the model performance for predicting maternal PK of emtricitabine in the third trimester with that of previously published PBPK models; and (5) compare different previously published approaches for estimating the placental permeability of these 2 drugs. Results showed that the pregnancy PBPK model for acyclovir predicted all maternal concentrations within a 2-fold error range, whereas the model for emtricitabine predicted 79% of the maternal concentrations values within that range. Extrapolation of these models to earlier stages of pregnancy indicated that the change in the median PK target parameters remained well above the target threshold. Concentrations of acyclovir and emtricitabine in the umbilical vein were overall adequately predicted. The comparison of different emtricitabine PBPK models suggested an overall similar predictive performance in the third trimester, but the comparison of different approaches for estimating placental drug permeability revealed large differences. These models can enhance the understanding of the PK behavior of renally excreted drugs, which may ultimately inform pharmacotherapeutic decision making in pregnant women and their fetuses.

Drug Transporters Expressed in the Human Placenta and Models for Studying Maternal-Fetal Drug Transfer

Tremendous efforts have been directed to investigate the ontogeny of drug transporters in fetuses, neonates, infants, and children based on their importance for understanding drug pharmacokinetics. During development (ie, in the fetus and newborn infant), there is special interest in transporters expressed in the placenta that modulate placental drug transfer. Many of these transporters can decrease or increase drug concentrations in the fetus and at birth, stressing the relevance of elucidating expression in the placenta and potential gestational age-dependent changes therein. Hence, the main objective of this review was to summarize the current knowledge about expression and ontogeny of transporters in the human placenta in healthy pregnant women. In addition, various in vitro, ex vivo, and in silico models that can be used to investigate placental drug transfer, namely, placental cancer cell lines, ex vivo cotyledon perfusion experiments, and physiologically based pharmacokinetic (PBPK) models, are discussed together with their advantages and shortcomings. A particular focus was placed on PBPK models because these models can integrate different types of information, such as expression data, ontogeny information, and observations obtained from the ex vivo cotyledon perfusion experiment. Such a mechanistic modeling framework may leverage the available information and ultimately help to improve knowledge about the adequacy and safety of pharmacotherapy in pregnant women and their fetuses.