Extrapolation of Upadacitinib Efficacy in Juvenile Idiopathic Arthritis Leveraging Pharmacokinetics, Exposure-Response Models, and Real-World Patient Data

Juvenile idiopathic arthritis (JIA) is the most prevalent pediatric rheumatic disease. While disease-modifying antirheumatic drugs (DMARDs), especially biologics, have greatly transformed the management of JIA, there remain some unmet medical needs that require new treatment options. The objective of this work was to describe and apply a modeling and simulation approach to extrapolate upadacitinib efficacy from the adult diseases, rheumatoid arthritis (RA) and psoriatic arthritis (PsA), to their respective pediatric diseases, polyarticular course JIA (pcJIA), and juvenile PsA (JPsA). A population pharmacokinetic model characterized upadacitinib pharmacokinetics in pediatric patients using data from two phase I studies in pediatric patients with pcJIA (N = 51) or atopic dermatitis (N = 33). Efficacy simulations were conducted using previously developed exposure-response models in adults with RA and PsA. Real-world pcJIA and JPsA patient databases were leveraged to construct representative patient profiles for the targeted population. Following administration of the proposed weight-based dosing regimen, the model-predicted median upadacitinib plasma exposures in pediatric patients were within 20% of those in adult RA and PsA patients receiving the approved adult regimen. Simulations demonstrate that upadacitinib efficacy in pcJIA and JPsA is predicted to be non-inferior to that in adults with RA or PsA, respectively. The results of this work enabled recent approvals of upadacitinib for the treatment of polyarticular JIA and JPsA in the United States. Upadacitinib safety in pediatrics is being further evaluated in ongoing clinical trials.