Population Pharmacokinetic-Pharmacodynamic Modeling of Variable Wear Times for a Dextroamphetamine Transdermal System
Authors: Castelli Mariacristina , Komaroff Marina , Meeves Suzanne , Balakrishnan Kanan , Baron Kyle T. , Mondick John T. , Faraone Stephen V. , Mattingly Gregory W. 
Published: April 2023

AbstractIntroductionThe Dextroamphetamine Transdermal System (d-ATS) was developed as an alternative to oral amphetamine (AMP) formulations for ADHD. In a pivotal study, d-ATS met primary and secondary efficacy endpoints for ADHD in children and adolescents. Study subjects wore d-ATS for 9 hours, and an improvement in Swanson, Kotkin, Agler, M-Flynn, and Pelham scale (SKAMP) total score was observed from 2 through 12 hours after application. Patients with ADHD may need varying durations of treatment for symptoms from day to day. This analysis describes the exposure-response (E-R) relationship for d-ATS and explores possible outcomes for wear times ≤9 hours under varying assumptions.MethodsA population pharmacokinetic (PK) model was developed to describe AMP disposition following d-ATS administration. This model was used to construct a population pharmacokinetic/pharmacodynamic (PK/PD) model from SKAMP total score data from two pediatric clinical studies to characterize onset and duration of effect after d-ATS administration. The integrated PK/PD model was used to describe the d-ATS E-R relationship and simulate the potential onset and duration of effect of d-ATS in response to various removal times (when <9 hours) by utilizing SKAMP scores as the efficacy measure. Subject-level AMP PK and SKAMP profiles were simulated for d-ATS removal at 4–9 hours post-application under different assumptions for AMP absorption after early patch removal. Modifications were made to the original population PK model to simulate patch removal.ResultsData from 81 children and 41 adolescents, 6–17 years old, were included. The model provided a reasonable description of the SKAMP score over time, showing an initial decline ~2 hours after patch application. In approximately 50% of children and adolescents, the maximum decline in SKAMP scores was observed within the first 4 hours after patch application. Earlier simulated d-ATS removal times were associated with reduced systemic exposure and earlier return to near-baseline scores across the range of assumptions tested.Under different assumptions, the graphs changed modestly but not dramatically. For example, with moderate/conservative assumptions, following a 9-hour wear time, SKAMP scores returned to within 90% of baseline value in ~49% of subjects by 12 hours and ~80% of subjects by 16 hours. Following a 4-hour wear time, percentages were ~74% by 12 hours and ~95% by 16 hours.ConclusionsSimulation results suggest that the duration of d-ATS efficacy may be related to wear time, which can be adjusted according to treatment needs, consistent with published observations for another transdermal stimulant. The d-ATS patch provides the ability to control medication exposure by shortening wear time, allowing treatment duration to be individualized and optimized in ADHD patients who have varying schedules and needs.FundingNoven Pharmaceuticals, Inc.