Paediatric extrapolation: A necessary paradigm shift

Efficacy and Safety of the Two-Drug Regimen Dolutegravir-Lamivudine in Adolescents Living With HIV-1 Naive to Antiretroviral Therapy at 48 Weeks (DANCE): A Single-Arm, Open-Label, Phase 3b Trial

BACKGROUND

Dolutegravir-lamivudine is recommended for initial antiretroviral therapy (ART) in adults living with HIV-1; however, no clinical trials have assessed this regimen in adolescents, a potentially more challenging population to treat. We evaluated efficacy, safety, and pharmacokinetics of dolutegravir-lamivudine as initial ART in adolescents living with HIV-1.

SETTING

Nine centers in Thailand, Kenya, and South Africa.

METHODS

In the single-arm, open-label, phase 3b DANCE study (NCT03682848), adolescents naive to ART aged ≥12 to <18 years, weighing ≥25 kg, with plasma HIV-1 RNA 1000 to ≤500,000 copies/mL received single once-daily dolutegravir-lamivudine fixed-dose combination tablet orally for 48 weeks (treatment phase). The primary endpoint was proportion of participants with HIV-1 RNA <50 copies/mL at Week 48 [Snapshot; intention-to-treat-exposed (ITT-E) population]. Safety outcomes were evaluated in the safety population. Both the ITT-E and safety populations consisted of participants who received ≥1 dose of dolutegravir-lamivudine (N = 32). A sensitivity analysis was performed using data from all but 2 participants who were withdrawn before Week 48 because of site closure (n = 30).

RESULTS

At Week 48, 26 of 32 (81%; 95% CI: 64 to 93) participants had HIV-1 RNA <50 copies/mL; in sensitivity analyses, 26 of 30 (87%; 95% CI: 69 to 96) participants achieved virologic suppression. No confirmed virologic withdrawals or deaths were reported. One drug-related adverse event was reported (grade 3 decreased glomerular filtration rate) and was the only adverse event leading to study withdrawal at data cut. Pharmacokinetic parameters were comparable with adult systemic exposure ranges.

CONCLUSIONS

Dolutegravir-lamivudine demonstrated efficacy and safety as initial ART in adolescents with HIV-1 through 48 weeks.

Exposure-Response Modeling in Adults and Adolescents With Schizophrenia to Support the Extrapolation of Brexpiprazole Efficacy to Adolescents

In order to accelerate drug development and avoid unnecessary drug trials in vulnerable pediatric populations, the US Food and Drug Administration (FDA) released a general advice letter to sponsors permitting the effectiveness of atypical antipsychotics for the treatment of schizophrenia in adults to be extrapolated to adolescents. Extrapolation is based on the evidence-based assumptions that (1) disease characteristics and (2) response to therapy, are similar in adults and adolescents. Whereas the FDA validated the extrapolation approach using data from multiple drug development programs, aripiprazole data are the most relevant to confirm the validity of the extrapolation approach for brexpiprazole, since aripiprazole and brexpiprazole both modulate dopaminergic and serotonergic signaling in the brain. The aims of this analysis were (1) to quantitatively assess the aripiprazole exposure (average steady-state concentration)-response (Positive and Negative Syndrome Scale total score change from baseline) similarity between adults and adolescents with schizophrenia, (2) to extend the aripiprazole exposure-response modeling to brexpiprazole using adult data, and (3) to use the brexpiprazole model to predict schizophrenia symptom response in adolescents. Disease-drug-dropout models were developed using patient-level data from clinical studies of aripiprazole (1007 adults, 294 adolescents) and brexpiprazole (1235 adults) in schizophrenia. The aripiprazole model demonstrated similar exposure-response between adults and adolescents with schizophrenia, validating the extrapolation approach. Extrapolation of the brexpiprazole adult exposure-response model to adolescents predicted the efficacy of brexpiprazole in adolescents aged 13-17 years with schizophrenia.

A Systematic Review of Uremic Toxin Concentrations and Cardiovascular Risk Markers in Pediatric Chronic Kidney Disease

Chronic kidney disease (CKD) can lead to cardiac dysfunction in a condition known as cardiorenal syndrome (CRS). It is postulated that the accumulation of uremic toxins in the bloodstream, as a consequence of declining kidney function, may contribute to these adverse cardiac effects. While CRS in adults has been extensively studied, there is a significant knowledge gap with pediatric patients. Uremic toxin levels in children remain inadequately characterized and quantified compared to adults. This review aims to systematically evaluate the association between uremic toxin concentrations and cardiac changes in pediatric CRS and to examine the impact of different dialysis modalities, specifically hemodialysis and peritoneal dialysis, on uremic toxin clearance and cardiovascular parameters. To address this, we conducted a systematic literature search of PubMed, following PRISMA guidelines. We used the terms "uremic toxins" and "cardiorenal syndrome" with variations in syntax to search for studies discussing the relationship between uremic toxin levels in CKD, the subsequent impact on cardiac parameters, and the emergence of cardiac dysfunction. Full-text articles written in English, conducted on humans aged from birth to 18 years, and published until December 2021 were included. A comprehensive literature search yielded six studies, and their risk of bias was assessed using JBI Critical Appraisal Checklists. Our systematic review is registered on PROSPERO, number CRD42023460072. This synthesis intends to provide an understanding of the role of uremic toxins in pediatric CRS. The findings reveal that pediatric patients with end-stage CKD on dialysis exhibit elevated uremic toxin levels, which are significantly associated with cardiovascular disease parameters. Additionally, the severity of CKD correlated with higher uremic toxin levels. No conclusive evidence was found to support the superiority of either hemodialysis or peritoneal dialysis in terms of uremic toxin clearance or cardiovascular outcomes. More pediatric-specific standardized and longitudinal studies are needed to develop targeted treatments and improve clinical outcomes and the quality of life for affected children.

Did pediatric drug development advance epilepsy treatment in young patients? It is time for new research goals

Modern drugs have changed epilepsy, which affects people of all ages. However, for young people with epilepsy, the framework of drug development has stalled. In the wake of the thalidomide catastrophe, the misconception emerged that for people < 18 years of age drugs, including antiseizure medications (ASMs), need separate proof of efficacy and safety, overall called "pediatric drug development". For ASMs, this has changed to some degree. Authorities now accept that ASMs are effective in < 18 years as well, but they still require "extrapolation of efficacy," as if minors were another species. As a result, some of the pediatric clinical epilepsy research over the past decades was unnecessary. Even more importantly, this has hampered research on meaningful research goals. We do not need to confirm that ASMs work before as they do after the 18th birthday. Instead, we need to learn how to prevent brain damage in young patients by preventing seizures and optimize ASMs' uses. Herein we discuss how to proceed in this endeavor.

Pediatric Market Access: A Qualitative Study

OBJECTIVES

This qualitative study aims to analyze current PM regulation and market access requirements and proposes potential solutions to mitigate current challenges.

METHODS

Twenty-two semi-structured interviews were conducted with experts from pharmaceutical industry, regulatory authorities, national health technology assessment (HTA) bodies, pediatricians, and academia from the Netherlands (NL), Germany (DE), the United Kingdom (UK), and France (FR) to get insight into the pediatric research, the regulatory and reimbursement processes, challenges, and solutions. Themes for further testing were developed on how to facilitate pediatric market access. Atlas.ti 9 was used to analyze the findings.

RESULTS

Heterogeneity in requirements for the European Medicines Agency (EMA) and HTA approvals are noted. By example, DE grants direct reimbursement after regulatory approval, the other countries require additional reimbursement which generate delays and challenges in patient access after marketing authorization. Key components in facilitating PM market access include multi-stakeholder collaboration, transparency, patient representatives, informed consent guidance, real-world evidence, and appropriate clinical trial designs. Pricing models based on the economic capabilities of individual countries could further reduce delays and challenges in market access. The additional specific pediatric incentives should be taken as best practice to encourage innovation in pediatric conditions.

CONCLUSION

This study highlights differences in requirements for regulatory and reimbursement approval, along with international differences in pricing and reimbursement procedures for pediatric market access.

Recent Use of Pediatric Extrapolation in Pediatric Drug Development in US

The regulatory standards of the United States Food and Drug Administration (FDA) require substantial evidence of effectiveness from adequate and well-controlled trials, for drugs developed in both adults and children. However, when scientifically justified, relying on extrapolation may be acceptable. Historically, the FDA's extrapolation approach was based on draft guidance published in 2014, which introduced the categories of full, partial, and no extrapolation. The European Medicines Agency (EMA) took a different view on pediatric extrapolation. To better understand the use of extrapolation to support pediatric drug development and approval, we reviewed the pediatric labeling changes published by the FDA, focusing on the labeling updates between 1/1/2015 and 7/31/2021, the period where the extrapolation approach is in transition to harmonize with the EMA. Within this time window, among the 265 drugs and biological products with pediatric labeling changes, 169 (63.8%) were identified where extrapolation was used. This includes 64 (24.2%) labeling changes, where full extrapolation was used, and 105 (39.6%) labeling changes, where partial extrapolation was used. The major disease areas that extrapolation was used include neuroscience (40/53, 75.5%) and infectious disease (20/28, 71.4%). The extrapolation approach was identified in terms of source population beyond the use of adult as well as extrapolation from clinical trials conducted in the same drug class. The use of extrapolation increased the rates of new and expanded pediatric indication in the period. This review gives the most recent landscape of pediatric labeling changes using extrapolation. With the released ICH (International Council for Harmonization) E11A guidance in April 2022, the paper also provides insights for future pediatric drug development programs.

Population Pharmacokinetic Analysis of Brexpiprazole to Support its Indication and Dose Selection in Adolescents With Schizophrenia

Due to the customary delay between medication approvals in adult and adolescent populations, adolescents with schizophrenia may receive off-label antipsychotic treatment, without empirically justified dosing recommendations. In order to accelerate pediatric drug development, the US Food and Drug Administration (FDA) released a general advice letter to sponsors permitting the effectiveness of atypical antipsychotics for the treatment of schizophrenia in adults to be extrapolated to adolescents based on a pharmacokinetic (PK) analysis to support dose selection, plus a safety study. The aim of the present article is to describe the population PK analysis that was submitted to the FDA to inform brexpiprazole dose selection in adolescents with schizophrenia. Using a population PK model with brexpiprazole clearance and volume of distribution allometrically scaled by body weight, PK simulations showed comparable brexpiprazole dose-exposure between adults and adolescents aged 13-17 years following oral daily doses of brexpiprazole 1-4 mg, indicating that the target brexpiprazole dose of 2-4 mg/day in adults with schizophrenia is also suitable for adolescents. Based on this population PK analysis, together with a safety study in adolescents, the FDA approved brexpiprazole for the treatment of schizophrenia in adolescents aged 13-17 years, via extrapolation of the efficacy of brexpiprazole from adults to adolescents.

Population Pharmacokinetic Modeling for Ceftazidime-Avibactam Renal Dose Adjustments in Pediatric Patients 3 months and Older

Ceftazidime-avibactam is a novel β-lactam/β-lactamase inhibitor combination developed to treat serious Gram-negative bacterial infections; approved indications include complicated urinary tract infection, complicated intra-abdominal infection, and hospital-acquired pneumonia including ventilator-associated pneumonia in patients ≥ 3 months old. Because of the predominantly renal clearance of ceftazidime and avibactam, dose adjustments (reductions) are required for patients with estimated creatinine clearance (CrCL) ≤ 50 mL/min. We describe the application of combined adult and pediatric population pharmacokinetic models in developing ceftazidime-avibactam dose recommendations for pediatric patients ≥ 2 to < 18 years old with body surface area-normalized CrCL ≤ 50 mL/min/1.73 m² , including moderate, severe, or very severe renal impairment, or end-stage renal disease requiring hemodialysis, and for patients ≥ 3 months to < 2 years old with mild, moderate, or severe renal impairment. Models included allometric scaling for all subjects and simulations (1,000 subjects per age group, renal function group, and indication) were performed nonparametrically using post hoc random effects. Doses were selected based on simulated pediatric patients achieving steady-state exposures similar to adults and high probability of target attainment (using a simultaneous joint target for both ceftazidime and avibactam). Because there were few children with renal impairment in the ceftazidime-avibactam clinical trials, selected pediatric doses were guided by extrapolation and matching of adult exposures associated with efficacy and within established safety margins. The recommended doses for pediatric patients with estimated CrCL ≤ 50 mL/min/1.73 m² use equivalent adjustments in dose quantity and/or administration interval (vs. the corresponding age group with normal renal function) as those for adults.

Implications of Pediatric Initiatives on CNS Drug Development for All Ages-2020 and Beyond: Second of Three Sets of Expanded Proceedings from the 2020 ISCTM Autumn Conference on Pediatric Drug Development

This article expands upon a session, titled "Implications of Pediatric Initiatives on CNS Drug Development for All Ages-2020 and Beyond," that was presented as part of a two-day meeting on pediatric drug development at the International Society for Central Nervous System (CNS) Clinical Trials and Methodology (ISCTM) Autumn Conference in Boston, Massachusetts, in October 2020. Speakers from various areas of pediatric drug development addressed a variety of implications of including children in drug development programs. The speakers wrote summaries of their talks, which are included here. The session's lead chair was Dr. Gahan Pandina, who wrote introductory and closing comments. Dr. Joseph Horrigan addressed the current landscape of pediatric development programs. Dr. Gahan Pandina addressed how the approach to research in pediatric populations affects the drug development process and vice versa. Dr. Alison Bateman-House discussed the ethical implications of research in the pediatric population. Dr. Luca Pani discussed some of the global regulatory issues and challenges concerning research in pediatric patients. Dr. Judith Kando served as a discussant and posed new questions about means of facilitating pediatric research. Finally, Dr. Gahan Pandina provided closing comments and tied together the presented issues. This paper should serve as an expert-informed reference to those interested and involved in CNS drug development programs that are aimed at children and/or required, through regulations, to include children as part of the approval process.

Innovations in Pediatric Therapeutics Development: Principles for the Use of Bridging Biomarkers in Pediatric Extrapolation

Even with recent substantive improvements in health care in pediatric populations, considerable need remains for additional safe and effective interventions for the prevention and treatment of diseases in children. The approval of prescription drugs and biological products for use in pediatric settings, as in adults, requires demonstration of substantial evidence of effectiveness and favorable benefit-to-risk. For diseases primarily affecting children, such evidence predominantly would be obtained in the pediatric setting. However, for conditions affecting both adults and children, pediatric extrapolation uses scientific evidence in adults to enable more efficiently obtaining a reliable evaluation of an intervention's effects in pediatric populations. Bridging biomarkers potentially have an integral role in pediatric extrapolation. In a setting where an intervention reliably has been established to be safe and effective in adults, and where there is substantive evidence that disease processes in pediatric and adult settings are biologically similar, a 'bridging biomarker' should satisfy three additional criteria: effects on the bridging biomarker should capture effects on the principal causal pathway through which the disease process meaningfully influences 'feels, functions, survives' measures; secondly, the experimental intervention should not have important unintended effects on 'feels, functions, survives' measures not captured by the bridging biomarker; and thirdly, in statistical analyses in adults, the intervention's net effect on 'feels, functions, survives' measures should be consistent with what would be predicted by its level of effect on the bridging biomarker. A validated bridging biomarker has considerable potential utility, since an intervention's efficacy could be extrapolated from adult to pediatric populations if evidence in children establishes the intervention not only to be safe but also to have substantive effects on that bridging biomarker. Proper use of bridging biomarkers could increase availability of reliably evaluated therapies approved for use in pediatric settings, enabling children and their caregivers to make informed choices about health care.

Current knowledge, challenges and innovations in developmental pharmacology: A combined conect4children Expert Group and European Society for Developmental, Perinatal and Paediatric Pharmacology White Paper

Developmental pharmacology describes the impact of maturation on drug disposition (pharmacokinetics, PK) and drug effects (pharmacodynamics, PD) throughout the paediatric age range. This paper, written by a multidisciplinary group of experts, summarizes current knowledge, and provides suggestions to pharmaceutical companies, regulatory agencies and academicians on how to incorporate the latest knowledge regarding developmental pharmacology and innovative techniques into neonatal and paediatric drug development. Biological aspects of drug absorption, distribution, metabolism and excretion throughout development are summarized. Although this area made enormous progress during the last two decades, remaining knowledge gaps were identified. Minimal risk and burden designs allow for optimally informative but minimally invasive PK sampling, while concomitant profiling of drug metabolites may provide additional insight in the unique PK behaviour in children. Furthermore, developmental PD needs to be considered during drug development, which is illustrated by disease- and/or target organ-specific examples. Identifying and testing PD targets and effects in special populations, and application of age- and/or population-specific assessment tools are discussed. Drug development plans also need to incorporate innovative techniques such as preclinical models to study therapeutic strategies, and shift from sequential enrolment of subgroups, to more rational designs. To stimulate appropriate research plans, illustrations of specific PK/PD-related as well as drug safety-related challenges during drug development are provided. The suggestions made in this joint paper of the Innovative Medicines Initiative conect4children Expert group on Developmental Pharmacology and the European Society for Developmental, Perinatal and Paediatric Pharmacology, should facilitate all those involved in drug development.

US Food and Drug Administration Facilitated Pediatric Approval Programs: Application to Pediatric Neurological Disorders

Crucial time is often lost while waiting for approval of therapies for pediatric neurological disorders, many of which have aggressive manifestations with devastating effects. There are logistical, ethical, and financial impediments that face the studies needed to determine efficacy and safety of therapies in children. In this article, the authors present the Food and Drug Administration's programs aimed at facilitating the development of pediatric drugs, focusing on their application to pediatric neurological disorders. They also provide examples of drugs that received, or are currently enrolled in, these programs. Reflecting upon the commonalities of drugs receiving these designations, the authors highlight underlying ethical issues related to pediatric drug development and emphasize the need for structured incentives to stimulate approval and production of drug therapies for pediatric neurology patients. By consolidating information that applies to drug approval of pediatric neurological disorders, stakeholders in drug development can enhance treatment development for these disorders.

Population Pharmacokinetic Modeling and Probability of Pharmacodynamic Target Attainment for Ceftazidime-Avibactam in Pediatric Patients Aged 3 Months and Older

Increasing prevalence of infections caused by antimicrobial-resistant gram-negative bacteria represents a global health crisis, and while several novel therapies that target various aspects of antimicrobial resistance have been introduced in recent years, few are currently approved for children. Ceftazidime-avibactam is a novel β-lactam β-lactamase inhibitor combination approved for adults and children 3 months and older with complicated intra-abdominal infection, and complicated urinary tract infection or hospital-acquired ventilator-associated pneumonia (adults only in the United States) caused by susceptible gram-negative bacteria. Extensive population pharmacokinetic (PK) data sets for ceftazidime and avibactam obtained during the adult clinical development program were used to iteratively select, modify, and validate the approved adult dosage regimen (2,000-500 mg by 2-hour intravenous (IV) infusion every 8 hours (q8h), with adjustments for renal function). Following the completion of one phase I (NCT01893346) and two phase II ceftazidime-avibactam studies (NCT02475733 and NCT02497781) in children, adult PK data sets were updated with pediatric PK data. This paper describes the development of updated combined adult and pediatric population PK models and their application in characterizing the population PK of ceftazidime and avibactam in children, and in dose selection for further pediatric evaluation. The updated models supported the approval of ceftazidime-avibactam pediatric dosage regimens (all by 2-hour IV infusion) of 50-12.5 mg/kg (maximum 2,000-500 mg) q8h for those ≥6 months to 18 years old, and 40-10 mg/kg q8h for those ≥3 to 6 months old with creatinine clearance > 50 mL/min/1.73 m2 .

An update on the use of allometric and other scaling methods to scale drug clearance in children: towards decision tables

INTRODUCTION

When pediatric data are not available for a drug, allometric and other methods are applied to scale drug clearance across the pediatric age-range from adult values. This is applied when designing first-in-child studies, but also for off-label drug prescription.

AREAS COVERED

This review provides an overview of the systematic accuracy of allometric and other pediatric clearance scaling methods compared to gold-standard PBPK predictions. The findings are summarized in decision tables to provide a priori guidance on the selection of appropriate pediatric clearance scaling methods for both novel drugs for which no pediatric data are available and existing drugs in clinical practice.

EXPERT OPINION

While allometric scaling principles are commonly used to scale pediatric clearance, there is no universal allometric exponent (i.e., 1, 0.75 or 0.67) that can accurately scale clearance for all drugs from adults to children of all ages. Therefore, pediatric scaling decision tables based on age, drug elimination route, binding plasma protein, fraction unbound, extraction ratio, and/or isoenzyme maturation are proposed to a priori select the appropriate (allometric) clearance scaling method, thereby reducing the need for full PBPK-based clearance predictions. Guidance on allometric scaling when estimating pediatric clearance values is provided as well.

Extrapolation as a Default Strategy in Pediatric Drug Development

Pediatric drug development lags adult development by about 8 years (Mulugeta et al. in Pediatr Clin 64(6):1185-1196, 2017). In such context, many incentives, regulations, and innovative techniques have been proposed to address the disparity for pediatric patients. One such strategy is extrapolation of efficacy from a reference population. Extrapolation is currently justified by providing evidence in support of the effective use of drugs in children when the course of the disease and the expected treatment response would be sufficiently similar in the pediatric and reference population. This paper's position is that, despite uncertainties, pediatric drug development programs should initially assume some degree of extrapolation. The degree to which extrapolation can be used lies along a continuum representing the uncertainties to be addressed through generation of new pediatric evidence. In addressing these uncertainties, the extrapolation strategy should reflect the level of tolerable uncertainty concerning the decision to expose a child to the risks of a new drug. This judgment about the level of tolerable uncertainty should vary with the context (e.g., disease severity, existing therapeutic options) and can be embedded into pediatric drug development archetypes to ascertain the extent of studies needed and whether simultaneous development for adults and adolescents be considered.

Extrapolation of Efficacy and Dose Selection in Pediatrics: A Case Example of Atypical Antipsychotics in Adolescents With Schizophrenia and Bipolar I Disorder

Pediatric labeling information for novel atypical antipsychotics can be significantly delayed as the result of time lag between initial drug approval in adults and the completion of pediatric clinical trials. This delay can lead health care providers to rely on limited evidence-based literature to make critical therapeutic decisions for pediatric patients. Effective and scientifically justified dosing recommendations are needed to improve treatment outcomes in pediatric patients with schizophrenia and bipolar I disorder. Extrapolation-based drug development strategies rely on leveraging prior data to reduce evidentiary requirements for newer data in establishing drug efficacy. On January 13, 2020, the US Food and Drug Administration (FDA) released a general advice letter to sponsors highlighting the acceptance of extrapolating efficacy of atypical antipsychotics to pediatric patients. This review provides insight into the FDA's justification for extrapolating efficacy from adult to pediatric patients and provides a rationale for dose selection in pediatric patients with schizophrenia and bipolar I disorder.

COVID-19 and Treatment and Immunization of Children-The Time to Redefine Pediatric Age Groups is Here

Children are infected with coronavirus disease 2019 (COVID-19) as often as adults, but with fewer symptoms. During the first wave of the COVID-19 pandemic, multisystem inflammatory syndrome (MIS) in children (MIS-C), with symptoms similar to Kawasaki syndrome, was described in young minors testing positive for COVID-19. The United States (US) Centers for Disease Control and Prevention (CDC) defined MIS-C as occurring in <21-year-olds, triggering hundreds of PubMed-listed papers. However, postpubertal adolescents are no longer children biologically; the term MIS-C is misleading. Furthermore, MIS also occurs in adults, termed MIS-A by the CDC. Acute and delayed inflammations can be triggered by COVID-19. The 18th birthday is an administrative not a biological age limit, whereas the body matures slowly during puberty. This blur in defining children leads to confusion regarding MIS-C/MIS-A. United States and European Union (EU) drug approval is handled separately for children, defined as <18-year-olds, ascribing non-existent physical characteristics up to the 18th birthday. This blur between the administrative and the physiological meanings for the term child is causing flawed demands for pediatric studies in all drugs and vaccines, including those against COVID-19. Effective treatment of all conditions, including COVID-19, should be based on actual physiological need. Now, the flawed definition for children in the development of drugs and vaccines and their approval is negatively impacting prevention and treatment of COVID-19 in minors. This review reveals the necessity for redefining pediatric age groups to rapidly establish recommendations for optimal prevention and treatment in minors.

Developmental Pharmacodynamics and Modeling in Pediatric Drug Development

Challenges in pediatric drug development include small patient numbers, limited outcomes research, ethical barriers, and sparse biosamples. Increasingly, pediatric drug development is focusing on extrapolation: leveraging knowledge about adult disease and drug responses to inform projections of drug and clinical trial performance in pediatric subpopulations. Pharmacokinetic-pharmacodynamic (PK-PD) modeling and extrapolation aim to reduce the numbers of patients and data points needed to establish efficacy. Planning for PK-PD and biomarker studies should begin early in the adult drug development program. Extrapolation relies on the assumption that both the underlying disease and the mechanism of action of the drug used to treat that disease are similar in adults and pediatric subpopulations. Clearly, developmental changes in PK and PD need to be considered to enhance the quality of PK-PD modeling and, therefore, increase the success of extrapolation. This article focuses on the influence of differences in PD between adults and pediatric subpopulations that are highly relevant for the use of extrapolation.

Use of a physiologically based pharmacokinetic-pharmacodynamic model for initial dose prediction and escalation during a paediatric clinical trial

AIMS

To build and verify a physiologically based pharmacokinetic (PBPK) model for radiprodil in adults and link this to a pharmacodynamic (PD) receptor occupancy (RO) model derived from in vitro data. Adapt this model to the paediatric population and predict starting and escalating doses in infants based on RO. Use the model to guide individualized dosing in a clinical trial in 2- to 14-month-old children with infantile spasms.

METHODS

A PBPK model for radiprodil was developed to investigate the systemic exposure of the drug after oral administration in fasted and fed adults; this was then linked to RO via a PD model. The model was then expanded to include developmental physiology and ontogeny to predict escalating doses in infants that would result in a specific RO of 20, 40 and 60% based on average unbound concentration following a twice daily (b.i.d.) dosing regimen. Dose progression in the clinical trial was based on observed concentration-time data against PBPK predictions.

RESULTS

For paediatric predictions, the elimination of radiprodil, based on experimental evidence, had no ontogeny. Predicted b.i.d. doses ranged from 0.04 mg/kg for 20% RO, 0.1 mg/kg for 40% RO to 0.21 mg/kg for 60% RO. For all infants recruited in the study, observed concentration-time data following the 0.04 mg/kg and subsequent doses were within the PBPK model predicted 5^th and 95^th percentiles.

CONCLUSION

To our knowledge, this is the first time a PBPK model linked to RO has been used to guide dose selection and escalation in the live phase of a paediatric clinical trial.

Dosing Common Medications in Hospitalized Pediatric Patients with Obesity: A Review

Medication management in children and adolescents with obesity is challenging because both developmental and pathophysiological changes may impact drug disposition and response. Evidence to date indicates an effect of obesity on drug disposition for certain drugs used in this population. This work identified published studies evaluating drug dosing, pharmacokinetics (PK), and effect in pediatric patients with obesity, focusing on 70 common medications used in a pediatric network of 42 US medical centers. A PubMed search revealed 33 studies providing PK and/or effectiveness data for 23% (16 of 70) of medications, 44% of which have just one study and can be considered exploratory. This work appraising 4 decades of literature shows several promising approaches: greater use of PK models applied to prospective clinical studies, dosing recommendations derived from both PK and safety, and multiyear effectiveness data on drugs for chronic conditions (e.g., asthma). Most studies make dose recommendations but are weakened by retrospective study design, small study populations, and no controls or historic controls. Dosing decisions continue to rely on extrapolating knowledge, including targeting systemic drug exposure typically achieved in adults. Optimal weight-based dosing strategies vary by drug and warrant prospective, controlled studies incorporating PK and modeling and simulation to complement clinical assessment.

Should Off Label Antiepileptic Drugs Be Used for Treatment of Infancy and Childhood Epilepsy? Discussions Based on a Dravet Syndrome Case Report

Epilepsy represents a burdensome neurological disorder with higher incidence before the age of 18 years. The treatment is medical and involves long-term administration of antiepileptic drugs (AED). There are known high-resistant syndromes with onset in infancy and childhood, Dravet syndrome, being one of them. It is a well-known fact that early seizures treatment prevents associated comorbidities, cognitive and motor disabilities, and improve long-term prognosis. There are several AEDs available but not all of them are approved for use in infants. This is due to the need for additional toxicology studies at this age and for development of suitable formulations.

A 14-month-old girl with Dravet syndrome was presented here. Prompt diagnosis was made based on clinical features and confirmed by the genetic tests. She partially responded to valproate and clobazam but continued to have prolonged febrile seizures. We added stiripentol after consulting reports of studies in infants younger than 2 years and after obtaining family consent. She responded well with decrease in episodes of status epilepticus and improvement in psychomotor development and stiripentol was tolerated well. Off label use of certain AEDs can benefit infants when there are no major pharmacokinetic differences in comparison to older children.

Commentary on the EMA Reflection Paper on the use of extrapolation in the development of medicines for paediatrics

Adopted guidelines reflect a harmonised European approach to a specific scientific issue and should reflect the most recent scientific knowledge. However, whilst EU regulations are mandatory for all member states and EU directives must be followed by national laws in line with the directive, EMA guidelines do not have legal force and alternative approaches may be taken, but these obviously require more justification. This new series of the BJCP, developed in collaboration with the EMA, aims to address this issue by providing an annotated version of some relevant EMA guidelines and regulatory documents by experts. Hopefully, this will help in promoting their diffusion and in opening a forum for discussion with our readers.

Paediatric extrapolation: A necessary paradigm shift

Legislative initiatives have been successful in increasing the availability of approved therapies for paediatric patients. However, additional measures to ensure the timely completion of paediatric studies are necessary to further increase the number of medicines available to children. Over the last 3 years, international experts convened to revise the ICH E11 guideline on clinical investigations of medicinal products in paediatric populations to harmonize approaches to paediatric extrapolation, striving to reduce substantial differences between regions in the acceptance of data for global paediatric medicine development programmes. Several areas of therapeutics development in children, such as human immunodeficiency virus and partial-onset seizures, have been streamlined and require fewer children enrolled in clinical trials because of the appropriate application of paediatric extrapolation. Based on this experience, it is clear that for paediatric extrapolation strategies to reach their full potential there is the need to understand the quality and quantity of data, often collected in adult patients, that will inform the appropriateness of the use of paediatric extrapolation, as well as to identify gaps in knowledge with respect to disease pathophysiology, organ maturation or drug target ontogeny. The generation of information that enhances our current understanding of these gaps in knowledge can further decrease the need for larger, paediatric clinical trials and can increase the efficiency of paediatric therapeutics development as well as protect children from participation in unnecessary studies. We hope that this publication will increase awareness, input and support from all the stakeholders involved in paediatric therapeutics development.