Ixekizumab Efficacy in Patients with Severe Peripheral Psoriatic Arthritis: A Post Hoc Analysis of a Phase 3, Randomized, Double-Blind, Placebo-Controlled Study (SPIRIT-P1)

Introduction The efficacy and safety of ixekizumab, an anti-interleukin-17A antibody, in patients with severe symptoms of psoriatic arthritis are largely unexplored. We report the efficacy and safety of ixekizumab in a post hoc analysis of the SPIRIT-P1 trial. Methods Patients were treated with placebo, ixekizumab 80 mg every 2 weeks (Q2W) or 4 weeks (Q4W), or adalimumab 40 mg Q2W for 24 weeks. In this subgroup analysis of SPIRIT-P1, the population with severe psoriatic arthritis was defined using the modified composite psoriatic activity index total score > 7 and peripheral arthritis score = 3 (> 4 tender or swollen joint count and ≥ 0.5 Health Assessment Questionnaire-Disability Index). Efficacy was measured by joint and skin endpoints including disease progression. Results In the severe population, significantly more patients ( p ≤ 0.001) treated with ixekizumab than placebo achieved 20% improvement according to the American College of Rheumatology criteria (ACR 20): 63.3% for ixekizumab Q4W, 60.4% for ixekizumab Q2W, and 24.5% for placebo. Statistically greater responses compared with placebo were observed in the severe population for ACR 50, ACR 70, ACR core set, disease activity index for psoriatic arthritis (DAPSA) low disease activity and DAPSA remission, and 28-joint disease activity score using C-reactive protein, as well as Psoriasis Area and Severity Index (PASI) 75, PASI 90, and PASI 100 ( p ≤ 0.001). Efficacy findings and the safety profile of ixekizumab in the severe population were consistent with those of the overall population, with no new safety concerns identified. Conclusions In patients with severe psoriatic arthritis, 24 weeks of treatment with ixekizumab resulted in improvements in both joint and skin symptoms. The safety profile in the severe population was consistent with the established safety profile of ixekizumab. Trial Registration ClinicalTrials.gov identifier, NCT01695239.