Impact of symptom duration on the short- and long-term efficacy of bimekizumab in axial spondyloarthritis: results up to 2 years

Bimekizumab, a monoclonal IgG1 antibody that selectively inhibits IL-17F in addition to IL-17A, showed efficacy to 2 years in patients with axial spondyloarthritis (axSpA). In this post hoc analysis, we compare the impact of shorter versus longer symptom duration on the efficacy of bimekizumab to Week 104. Efficacy outcomes by symptom duration (≤ 2 [ASAS early axSpA definition] versus > 2 years; ≤ 5 versus > 5 years) were assessed across patients from BE MOBILE 1 and 2 (non-radiographic [NCT03928704]/radiographic axSpA [NCT03928743]) and the combined open-label extension (NCT04436640). (Relative) odds ratios and (relative) differences were calculated to compare 16-week bimekizumab versus placebo treatment effect and 104-week outcomes, and infer the significance of differences, between symptom duration subgroups. Analyses were neither powered for these comparisons nor multiplicity adjusted, and should be interpreted accordingly. Improved disease activity, physical function, fatigue, health-related quality of life and objective signs of inflammation were seen with bimekizumab versus placebo at Week 16 regardless of symptom duration. Outcomes were then sustained or improved with bimekizumab to Week 104 across all subgroups. 16-week bimekizumab versus placebo treatment effect was comparable between subgroups (e.g., ≤ 2-year versus > 2-year symptom duration relative odds ratio [95% CI] for ASDAS < 2.1 in BE MOBILE 1: 0.82 [0.22, 3.08]). Significant differences were observed for some 104-week outcomes between symptom duration subgroups across both studies (e.g., ≤ 5-year versus > 5-year symptom duration odds ratio [95% CI] for ASDAS < 2.1 in BE MOBILE 2: 1.94 [1.02, 3.68]), all favouring the shorter symptom duration subgroups. Bimekizumab was efficacious to 2 years regardless of symptom duration, with comparable 16-week treatment effect but generally better 104-week outcomes in the shorter versus longer symptom duration subgroups. Registered on ClinicalTrials.gov; NCT03928704 (BE MOBILE 1; 23rd April 2019), NCT03928743 (BE MOBILE 2; 23rd April 2019), NCT04436640 (BE MOVING; 15th June 2020).