The effect of ixekizumab on axial manifestations in patients with psoriatic arthritis from two phase III clinical trials: SPIRIT-P1 and SPIRIT-P2

BACKGROUND: Psoriatic arthritis (PsA) is a chronic inflammatory condition predominantly affecting the peripheral joints. However, some patients with PsA can experience axial involvement which is manifested with back pain and associated with increased burden of illness. OBJECTIVES: The aim of this post hoc analysis was to determine the efficacy of ixekizumab (IXE) up to 52 weeks in reducing axial symptoms in PsA patients, presenting with axial manifestations. DESIGN: This was a post hoc analysis of two pooled phase III clinical trials. METHODS: Patients with axial manifestations, from two placebo-controlled, randomized, double-blind, phase III trials (SPIRIT-P1 and SPIRIT-P2), were defined as Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) Question 2 (Q2; back pain)] total score ⩾4 and average of BASDAI Q5 + Q6 (morning stiffness) ⩾4 at baseline. For this post hoc analysis, the efficacy of IXE was evaluated at weeks 16, 24, and 52 using separate BASDAI questions (including back pain and morning stiffness), total BASDAI and modified BASDAI (mBASDAI; without Q3), Ankylosing Spondylitis Disease Activity Score (ASDAS), and 50% improvement in BASDAI (BASDAI50) response. Treatment comparisons were performed using logistic regression and analysis of covariance model for categorical and continuous end points, respectively. RESULTS: In the post hoc analysis among PsA patients with axial manifestations at baseline (N = 313), improvements in back pain and morning stiffness at weeks 16 and 24 were significantly greater in patients receiving IXE versus placebo (both p < 0.001). Improvements in BASDAI individual scores and total scores, mBASDAI, and ASDAS were significantly greater in patients receiving IXE compared with placebo. Similarly, significantly more IXE-treated patients achieved BASDAI50 at weeks 16 and 24 versus placebo. The effect of IXE was sustained at week 52. Similar effects were observed in sensitivity analyses subgroups. CONCLUSION: IXE is effective in improving axial symptoms in patients with active PsA presenting with axial manifestations.