Stipe Ćavar, Frane Grubišić, Hana Skala Kavanagh, Ines Doko Vajdić, Krunoslav Bojanić, Simeon Grazio

Objective: To compare the effectiveness and persistence of TNF-α inhibitors (TNF-αi) and IL-17 inhibitors (IL-17i) in the treatment of patients diagnosed with axial spondyloarthritis (axSpA), who received these medications as first-line biological therapy in everyday clinical practice conditions. Subjects and methods: In this observational longitudinal study, sociodemographic, clinical, and laboratory data, as well as the duration of treatment and reasons for therapy discontinuation, were collected for 112 patients with a confirmed diagnosis of axSpA treated with TNF-αi and IL-17i from January 2017 to January 2023 at the Clinic for Rheumatology, Physical
Medicine, and Rehabilitation of KBC-Sestre milosrdnice. Parameters of interest were recorded immediately before the start of biological therapy (0th visit), and after 3 months (1st visit), 9 months (2nd visit), 15 months (3rd visit), and 21 months from the first visit or at the end of the treatment (4th visit). In addition to descriptive statistics, T-tests or Wilcoxon tests, ANOVA with post hoc multiple comparisons, and Chi-square tests were used to compare the two groups of biological drugs. The significance level was set at α<0.05. Results: Significant differences were found in the key disease activity parameters between individual control visits, as expected and in accordance with the effectiveness of biological drugs. Compared to patients treated with IL-17i, patients treated with TNF-αi had a
shorter duration of morning stiffness at the 3rd (χ²=8.5, p=0.01) and 4th (χ²=9.1, p=0.01) visits, and a lower rate of CRP increase at the 4th visit (χ²=7.1, p=0.01), while no significant differences were observed in other monitored parameters between the two drug groups. The median duration of the treatment was 22 months (IQR 27, range 2–70) for the TNF-α group and 30 months (IQR 35.8, range 1–76) for the IL-17 group, without significant difference (W=1625.5, p=0.08). In the TNF-α inhibitor group, 58 (75.3%) patients remained on the same drug, while in the IL-17 group, this was the case in 26 (74.3%) patients, with no difference in switching to the second line of treatment (χ²=0.01, p=1). Conclusion: Our data suggest comparable effectiveness and persistence of IL-17 inhibitors and TNF-α inhibitors used as first-line biological therapy in patients with axSpA.