INTRODUCTION: This study aimed to demonstrate the interchangeability of biosimilar CT-P17 and European Union reference adalimumab (EU-adalimumab) in a repeated-switch scenario. METHODS: In this ongoing, randomized, double-blind, active-controlled, phase 3 study, adults with moderate-to-severe plaque psoriasis received 80 mg EU-adalimumab on day 1, then 40 mg 1 week later and every other week until week 11. At week 13, patients were randomized (1:1, via an interactive web response system) to continue EU-adalimumab ("continuous" group) or undergo repeated switches between CT-P17 and EU-adalimumab ("switching" group). Dosing was via subcutaneous administration. The primary endpoints were area under the concentration-time curve and maximum serum concentration between weeks 25 and 27 (AUC RESULTS: The first patient provided signed informed consent on November 7, 2022. Week 27 visits were completed by August 14, 2023. Of 367 patients enrolled, 346 were randomized (switching group, n = 172
continuous group, n = 174). The ratios of least squares means between groups and associated 90% confidence intervals (CIs) for AUC CONCLUSIONS: Week 27 primary PK results demonstrated bioequivalence, and the overall study results supported the interchangeability of CT-P17 and EU-adalimumab. TRIAL REGISTRATION: ClinicalTrials.gov, NCT05495568.