(031) Real-World Patterns in Treatment Switching to Biosimilar Adalimumab in the United States

Background: Adalimumab (Humira), a biologic medication used to treat a variety of inflammatory conditions, had market exclusivity in the US for over 20 years. The first biosimilar, adalimumab-atto (Amjevita), was introduced on January 31, 2023. Eight adalimumab biosimilars are now available in the US. Despite the lower cost of biosimilars, patients may be reluctant to switch because biosimilars are not identical to bio-originator adalimumab.

Objectives: To describe patterns in switching from bio-originator to biosimilar adalimumab in the US, including trends over time and patient characteristics

Methods: Using a subset of EHR data from Truveta, we identified a cohort of patients with an outpatient office or telehealth encounter and at least 2 dispenses of adalimumab in the year before biosimilar availability (1/31/22-01/31/23), and at least one outpatient office or telehealth encounter in the year since availability (1/31/23 – 1/31/24). Truveta Data included encounters, prescriptions, conditions, medication dispensing, and social drivers of health (SDOH) for a collective of US healthcare systems. We describe the number and percentage of eligible patients with evidence of bio-originator to biosimilar switching, defined as a new prescription or medication dispense for any biosimilar since 1/31/23. The monthly rate of switching over time was calculated as the number of patients with evidence of switching divided by the number of cohort patients with an encounter who had not yet switched.

Results: Of 30,720 eligible patients on adalimumab who met study criteria, 317 (1%) had evidence of switching to a biosimilar. Patients who switched (cohort overall) had a median age of 52.6 (52.7) years, 63% (65%) were female, 82% (77%) were white, and 6% (4%) had annual incomes <$25,000. Compared to the cohort overall, patients who switched had similar prevalence of rheumatoid arthritis (34% of those who switched vs. 33% overall; p = 0.5), psoriasis (24% vs. 26%; p = 0.5), psoriatic arthritis (16% vs. 15%; p = 0.8), and ankylosing spondylitis (10% vs. 8%; p = 0.11), but higher rates of Crohn’s disease (24% vs. 17%; p < 0.01) and ulcerative colitis (12% vs. 9%; p < 0.05). Rates of switching were similar in February 2023 (3.36 per thousand patients with encounters) and December 2023 (3.31).

Conclusions: In the initial period of biosimilar availability, switching from bio-originator adalimumab to biosimilars remained uncommon. Importantly, the largest pharmacy benefits manager in the US will remove bio-originator adalimumab from some formularies in April 2024, which may accelerate adoption of biosimilars. This work will be updated to reflect the most recent trends available.