Real-world switching and switch-back patterns among patients transitioning from adalimumab to biosimilars in the United States (February 2023 to August 2025)

BACKGROUND: Adalimumab is a widely used biologic for autoimmune diseases. Biosimilars to adalimumab became available in 2023 and were expected to improve affordability and access, yet real-world evidence on switching after biosimilar initiation remains limited. OBJECTIVE: To assess adoption of adalimumab biosimilars and characterize the frequency and timing of switch-backs to originator adalimumab. METHODS: This retrospective cohort study used Truveta Data, a deidentified electronic health record dataset. Adult patients were included if they had at least 1 outpatient or telehealth encounter between February 1, 2023, and August 31, 2025, and at least 2 originator adalimumab dispenses in the prior year. Switching was defined as the first biosimilar dispense following originator use, and switch-back was defined as a subsequent originator dispense after biosimilar initiation. Multivariable logistic regression identified characteristics associated with switch-back, and a Cox proportional hazards model evaluated factors associated with earlier switch-back (≤30 days). RESULTS: Among 67,594 patients treated with originator adalimumab, 17.7% (n = 11,947) switched to a biosimilar during the study period. Switching peaked in April 2024, coinciding with formulary changes. Among 9,252 biosimilar initiators, with at least 1 clinical encounter at least 90 days after a biosimilar dispense, 16.0% (n = 1,478) switched back to the originator. Older adults (≥65 years and 50-64 years) had higher odds of switching back (odds ratio [OR] = 2.05 [95% CI = 1.64-2.56] and OR = 1.23 [95% CI = 1.03-1.46], respectively), as did women (OR = 1.19; 95% CI = 1.05-1.34) and patients with ankylosing spondylitis (OR = 1.32; 95% CI = 1.10-1.58). Rural residence was associated with higher odds of early switch-back (OR = 1.80; 95% CI = 1.20-2.70). CONCLUSIONS: Biosimilar uptake increased following formulary changes, yet more than 1 in 7 biosimilar initiators returned to originator adalimumab. Variation in early switch-back and patient characteristics highlights the importance of real-world evidence to understand biosimilar adoption beyond formulary-driven transitions.