Patient tolerability of adalimumab biosimilar therapy in dermatology and rheumatology: real-world experience from a large tertiary centre

Abstract Adalimumab is widely used in the treatment of immune-mediated inflammatory diseases. It is the highest-spend drug in the National Health Service, costing more than £400 million annually. In 2018, adalimumab biosimilars became available, leading to substantial cost savings. However, patient tolerability of biosimilars remains underexplored. We evaluated the tolerability of adalimumab biosimilar therapy (Idacio®) in patients who were switched from Humira® in a large dermatology and rheumatology tertiary centre. We identified all patients issued with a prescription of Humira by dermatology [psoriasis and hidradenitis suppurativa (HS)] or rheumatology (rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis and Behçet disease) and analysed the number who switched to Idacio between January 2021 and March 2022. Patient electronic records were reviewed up to October 2022 to identify patients who switched back to the originator product and the documented reason for the switch. The primary outcome was the numbers of patients who were switched back from the biosimilar to the originator product. Of 769 patients issued with a prescription of Humira, 694 were switched to Idacio during the study period. Of these, 134 (19.3%) switched back to the originator product, 102 of whom (76.1%) remained on this during follow-up. The highest proportion of individuals switching back to the originator product was observed in the HS population (26.7%). The most common reasons for switching back were patient-reported loss of disease control (n = 63; 47.0%), injection pain (n = 51; 38.1%) or both (n = 10; 7.5%). The median time to switch back was 197 days (interquartile range 138–280). Of 694 patients prescribed Idacio, 32 (4.6%) were switched to an alternative biologic agent during the study period. Our experience with previous biosimilar switches within rheumatology and dermatology (etanercept, rituximab and infliximab) has resulted in few patients requiring a switch back to the originator. Our data indicate that around one in five patients in our study population switched back to the originator product. The higher proportion of patients citing injection pain may relate to the citrate excipient content or larger injection volume of the biosimilar Idacio. Loss of efficacy with time is well established with adalimumab, in part due to antidrug antibodies, and cannot be specifically attributed to the biosimilar. Switching may alter a patient’s confidence in the drug, which is particularly important when it may be a first-line therapy or the only approved biologic for a condition. Data on switch-back rates for other adalimumab biosimilars is required to understand how generalizable our findings are and the potential economic implications.