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

An overview of the efficacy and safety of brexpiprazole for the treatment of schizophrenia in adolescents

INTRODUCTION

The onset of psychotic symptoms occurs prior to age 19 in 39% of the patients with schizophrenia. There are limited approved treatment options for adolescents with schizophrenia. Brexpiprazole was approved by the United States Food and Drug Administration (FDA) for treatment of schizophrenia in adolescents in 2022.

AREAS COVERED

Extrapolation of adult data to youth and use of pharmacologic modeling coupled with open long-term safety data were used by the FDA to approve brexpiprazole for adolescent schizophrenia. They were all reviewed herein.

EXPERT OPINION

D2 receptor partial agonist antipsychotic agents are preferred in the early phase of treatment of psychotic disorders. Approval of brexpiprazole in adolescent schizophrenia provides an additional option. Brexpiprazole was approved by the FDA on the basis of extrapolation of adult data without controlled trials in adolescents. This reduces placebo exposure in young people. Two previous agents (asenapine and ziprasidone) approved for adult schizophrenia failed to separate from placebo in adolescent schizophrenia studies; this partially undermines the process of extrapolation. For brexpiprazole, the paucity of data in adolescents relegates it to a second-line agent. More research on brexpiprazole is needed to delineate its relative role in the management of adolescent 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 Modeling and Stochastic Simulations to Support Pediatric Dose Selection of Pimavanserin

Pimavanserin is a selective serotonin-modulating agent with inverse agonist/antagonist activity at the 5-hydroxytryptamine2A (5-HT2A ) receptor. The safety and efficacy of pimavanserin 34 mg once daily were studied in adults with hallucinations and delusions associated with Parkinson's disease psychosis and other neuropsychiatric conditions. This analysis used model-based simulations of pimavanserin steady-state exposures to identify a dose that generated pediatric exposures comparable with adult exposures achieved with 34 mg pimavanserin. A population pharmacokinetics model was developed using pooled plasma drug concentration (ie, actual) data from 13 clinical studies, including a phase 1 study of adolescent pediatric patients (aged 13-17 years) with various psychiatric conditions. Stochastic simulations were performed to predict exposures in a virtual (ie, simulated) group of pediatric patients (aged 5-17 years). Steady-state measures of the area under the plasma concentration-time curve (AUC) and maximum drug concentration (Cmax ) were simulated for relevant age and weight stratifications and compared with simulated exposures in adults (aged 18-49 years). The simulated mean AUC ranged from 47.41 to 54.73 ng d/mL and the mean Cmax ranged from 41.13 to 50.07 ng/mL in adults receiving pimavanserin 34 mg. The simulated mean (SD) Cmax of 56.54 (24.58) ng/mL with pimavanserin 34 mg in patients aged 10-17 years was similar to that in adults. Pimavanserin 20 mg yielded a mean (SD) Cmax of 45.30 (21.31) ng/mL in patients aged 5-9 years and 49.18 (22.91) ng/mL in the pediatric patient weight group of 14-25 kg, which are values close to the Cmax in adults treated with 34 mg. Pimavanserin 20 and 34 mg in pediatric patients aged 5-9 and 10-17 years, respectively, yielded exposures similar to daily pimavanserin 34 mg in adults aged 18-49 years.

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.

Review: Role of Model-Informed Drug Development Approaches in the Lifecycle of Drug Development and Regulatory Decision-Making

Model-informed drug development (MIDD) is a powerful approach to support drug development and regulatory review. There is a rich history of MIDD applications at the U.S. Food and Drug Administration (FDA). MIDD applications span across the life cycle of the development of new drugs, generics, and biologic products. In new drug development, MIDD approaches are often applied to inform clinical trial design including dose selection/optimization, aid in the evaluation of critical regulatory review questions such as evidence of effectiveness, and development of policy. In the biopharmaceutics space, we see a trend for increasing role of computational modeling to inform formulation development and help strategize future in vivo studies or lifecycle plans in the post approval setting. As more information and knowledge becomes available pre-approval, quantitative mathematical models are becoming indispensable in supporting generic drug development and approval including complex generic drug products and are expected to help reduce overall time and cost. While the application of MIDD to inform the development of cell and gene therapy products is at an early stage, the potential for future application of MIDD include understanding and quantitative evaluation of information related to biological activity/pharmacodynamics, cell expansion/persistence, transgene expression, immune response, safety, and efficacy. With exciting innovations on the horizon, broader adoption of MIDD is poised to revolutionize drug development for greater patient and societal benefit.