Background: The patent for adalimumab originator expired in 2018 in the United Kingdom. Subsequently, four adalimumab biosimilars were launched. National Health Service England undertook a managed market share tender to ensure plurality of suppliers and price competition over the longer term. Each hospital was subsequently allocated a preferred brand of adalimumab biosimilar. Here we describe our experience of switching patients with inflammatory arthritis from adalimumab originator to the biosimilar, ABP 501 in a single centre.

Objectives: To evaluate the proportion of patients successfully switched from adalimumab originator to ABP 501 focusing on drug retention, reasons for remaining on originator and reasons for switching back from biosimilar to originator.

Methods: A retrospective analysis was completed on the cohort of 287 rheumatology patients who were prescribed adalimumab originator prior to the switch to ABP 501. Case notes were analysed to identify whether patients remained on biosimilar 24 weeks after switching from originator.

Results: 99% patients on adalimumab originator (283/287) were switched to ABP 501 within 32 weeks, starting from February 2019. 1% (4/287) remained on originator due to a confirmed latex allergy, as the needle cover of the ABP 501 pre-filled syringe consists of dry natural rubber. 4% (12/283) of patients who switched to biosimilar reverted to originator (1 patient per 2 weeks over 24 weeks). 3% (9/283) of patients who switched to biosimilar were no longer receiving any adalimumab therapy. Reasons for ceasing therapy included recurrent infections (4/9) and progression to the next line of biologics/small molecule therapy (5/9). 93% (262/283) remained stable on ABP 501 (Table). Applications to revert to originator were reviewed by a Biosimilar Steering Group (BSG). The BSG assessment included a review of disease activity, reported symptoms and adverse reactions before and after the switch to biosimilar. Approval to revert to originator occurred in patients who had a clear increase in disease activity or newly reported adverse reactions. If the patient had active disease prior to switch, a change to non-adalimumab therapy would be recommended instead. Of the 12 patients who reverted to originator, 7 (58%) did so due to reduced effectiveness, 3 (25%) due to adverse reactions, and 2 (17%) due to both. Adverse reactions reported within 24 hours of the first injection included nausea, anxiety, insomnia, tinnitus, dizziness, headaches and injection-site reactions. Patients also reported hair loss, fatigue and mouth ulcers. Reported adverse reactions ceased once biosimilar was stopped and/or switching back to originator. All patients who reverted to originator due to reduced effectiveness reported a reduction in disease activity and improvement in symptoms.

Conclusion: The vast majority of patients in our cohort on adalimumab were successfully switched from originator to ABP 501. The adalimumab biosimilar has been generally well-tolerated. 93% remained on biosimilar 24 weeks after switching, 4% have switched back to originator and 3% have either stopped or changed treatment. Reasons for switching back to originator from biosimilar included adverse reactions, most of which occurred within 24 hours, and also worsening of symptoms.

Disclosure of Interests: None declared