ABSTRACT
AIM: This study, FKB327-003, is a phase 3, open-label extension (OLE) study comparing the long-term immunogenicity of an adalimumab biosimilar, FKB327 (F), with the reference product (RP). METHODS: In the OLE, patients completing 24 weeks of an initial randomized, double-blind (DB) study (Period 1) with clinical response and no safety concerns were rerandomized to F or RP, so that two-thirds of patients remained on the same treatment and one-third switched to the alternate treatment for weeks 24 through 54 (OLE weeks 0-30; Period 2), then all received F through week 100 (OLE week 76; Period 3). Treatment sequences were F-F-F (no switch), RP-F-F and RP-RP-F (single switch), and F-RP-F (double switch). Patients who entered the OLE study were evaluated for immunogenicity across switching sequences. RESULTS: The proportion of patients with positive antidrug antibody (ADA) status at the end of Period 1 was 61.7% and 60.0% for F and RP, respectively. The proportion of patients with positive ADA status did not increase throughout Period 1, and was similar for F and RP at all time points. At the end of Period 3, the proportion of patients with positive ADA status was lower in all treatment sequences, at 51.1%, 54.4%, 48.1%, and 42.5% for F-F-F, F-RP-F, RP-F-F, and RP-RP-F, respectively. CONCLUSION: The RP and F showed comparable immunogenicity characteristics after long-term administration. Development of ADAs with the RP and F was similar, and was not impacted by switching and double switching between F and RP treatment.