Pharmacokinetics, Efficacy, and Safety of Upadacitinib in Pediatric Patients with Polyarticular-Course Juvenile Idiopathic Arthritis: An Interim Analysis of an Open-label, Phase 1 Trial.

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This work aimed to evaluate the pharmacokinetics, efficacy, and safety of upadacitinib, an oral selective JAK inhibitor, in pediatric patients with polyarticular-course juvenile idiopathic arthritis (pcJIA). In an open-label, phase 1 study (SELECT-YOUTH), enrolled patients, aged 2 to <18 years with pcJIA, received bodyweight-based upadacitinib doses using a twice-daily (BID) oral solution or once-daily (QD) extended-release tablet based on their body weight and ability to swallow tablets. The study included a 7-day pharmacokinetic assessment, followed by a long-term efficacy and safety evaluation for up to 156 weeks, including an additional long-term safety cohort. This interim analysis included available pharmacokinetic and safety data and efficacy data collected through Week 48. A total of 57 patients received upadacitinib. The median time to maximum upadacitinib concentration was approximately 3 hours and 1 hour for the tablet and oral solution regimens, respectively; the harmonic mean functional half-life was approximately 5 hours and 2 hours, respectively. Juvenile idiopathic arthritis (JIA) American College of Rheumatology (ACR)30/50/70/90/100 responses at Week 12 were 91.8/89.8/69.4/49.0/32.7%, respectively. Efficacy was generally maintained through Week 48, and improvement in additional efficacy endpoints was also observed. At a median exposure duration of 412 days, 52 of 57 patients reported adverse events, of these 6 experienced serious adverse events. Adverse events were predominately mild to moderate in severity and consistent with the known safety profile of upadacitinib. This interim analysis demonstrates that the bodyweight-based dosing regimen of upadacitinib was well tolerated and efficacious in pediatric patients with pcJIA.