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Objective.To evaluate the efficacy and safety of ixekizumab (IXE), an interleukin 17A antagonist, in patients with psoriatic arthritis (PsA) after 52 weeks in a phase III study.Methods.Patients were initially randomly assigned to IXE 80 mg every 2 weeks (IXEQ2W) or every 4 weeks (IXEQ4W) after a 160-mg starting dose, placebo (PBO), or adalimumab (ADA) 40 mg Q2W. At Week 24 (Week 16 for inadequate responders), ADA (8-week washout before starting IXE) and PBO patients were rerandomized to IXEQ2W or IXEQ4W. Six treatment groups were evaluated in the extension period (weeks 24–52): IXEQ2W/IXEQ2W, IXEQ4W/IXEQ4W, ADA/IXEQ2W, ADA/IXEQ4W, PBO/IXEQ2W, and PBO/IXEQ4W. The extension period population (EPP) included patients who received ≥ 1 dose of study medication during the extension period.Results.There were 381/417 (91.4%) patients who entered the extension period. In the IXEQ4W/IXEQ4W and IXEQ2W/IXEQ2W groups (EPP), respectively, American College of Rheumatology (ACR)20 (69.1% and 68.8%), ACR50 (54.6% and 53.1%), and ACR70 (39.2% and 39.6%) response rates were sustained at Week 52. Patients rerandomized to IXE also demonstrated efficacy measured by ACR response rates at Week 52. A similar pattern was observed for Psoriasis Area and Severity Index outcomes. Radiographic progression in all 6 groups was minimal. The most frequently reported treatment-emergent adverse events (≥ 4%) were nasopharyngitis, injection site reaction, injection site erythema, upper respiratory tract infection, and back pain. No deaths were reported, and serious adverse event frequency was 0–4% with IXE.Conclusion.During the extension period, IXEQ4W or IXEQ2W treatment demonstrated sustained efficacy in key PsA domains with a safety profile consistent with other studies investigating IXE. Clinical trial number: NCT01695239; EudraCT 2011-002326-49.