ObjectiveTo evaluate the efficacy and safety of apremilast, an oral phosphodiesterase 4 inhibitor, in patients with active ankylosing spondylitis (AS).MethodsThis phase III, multicenter, double-blind, placebo-controlled study (ClinicalTrials.gov: NCT01583374) randomized patients with active AS (1:1:1) to placebo, apremilast 20 mg twice daily, or apremilast 30 mg twice daily for 24 weeks, followed by a long-term extension phase (up to 5 yrs). The primary endpoint was Assessment of the Spondyloarthritis international Society 20 (ASAS20) response at Week 16. The effect of treatment on radiographic outcomes after 104 weeks was assessed using the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS).ResultsIn total, 490 patients with active AS were randomized in the study (placebo: n = 164; apremilast 20 mg twice daily: n = 163; apremilast 30 mg twice daily: n = 163). The primary endpoint of ASAS20 response at Week 16 was not met (placebo: 37%; apremilast 20 mg twice daily: 35%; apremilast 30 mg twice daily: 33%; P = 0.44 vs placebo). At Week 104, mean (SD) changes from baseline in mSASSS were 0.83 (3.6), 0.98 (2.2), and 0.57 (1.9) in patients initially randomized to placebo, apremilast 20 mg twice daily, and apremilast 30 mg twice daily, respectively. The most frequently reported adverse events through Week 104 were diarrhea, nasopharyngitis, upper respiratory infection, and nausea.ConclusionNo clinical benefit was observed with apremilast treatment in patients with active AS. The safety and tolerability of apremilast were consistent with its known profile.