A Quantitative Justification of Similarity in Placebo Response Between Adults and Adolescents With Acute Exacerbation of Schizophrenia in Clinical Trials

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.

Pediatric Extrapolation Approach for U.S. Food and Drug Administration Approval of Brexpiprazole in Patients Aged 13 to 17 Years with Schizophrenia

A pharmacokinetic (PK) bridging approach was successfully employed to support the dosing regimen and approval of brexpiprazole in pediatric patients aged 13-17 years with schizophrenia. Brexpiprazole was approved in 2015 for the treatment of schizophrenia and the adjunctive treatment of major depressive disorder in adults based on efficacy and safety data from clinical trials. On January 13, 2020, the US Food and Drug Administration issued a general advice letter to sponsors highlighting the acceptance of efficacy extrapolation of certain atypical antipsychotics from adult patients to pediatric patients considering the similarity in disease and exposure-response relationships. Brexpiprazole is the first atypical antipsychotic approved in pediatrics using this approach. The PK data available from pediatric patients aged 13-17 years have shown high variability due to the limited number of PK evaluable subjects, which limits a robust estimation of differences between adult and pediatric patients. The PK model-based approach was thus utilized to evaluate the appropriateness of the dosing regimen by comparing PK exposures in pediatric patients aged 13-17 years with exposures achieved in adults at the approved doses. In addition to exposure matching, safety data from a long-term open-label clinical study in pediatric patients informed the safety profile in pediatric patients. This report illustrates the potential of leveraging previously collected efficacy, safety, and PK data in adult patients to make a regulatory decision in pediatric patients for the indication of schizophrenia.

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.

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.

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.