Safety and Efficacy Study of Apremilast to Treat Psoriatic Arthritis

This is a Phase 3b, multicenter, randomized, double-blind, placebo-controlled, parallel-group study to evaluate the efficacy and safety of apremilast monotherapy in subjects with active psoriatic arthritis. Approximately 214 subjects will be randomized in a 1:1 ratio to either apremilast 30 mg BID (twice a day) or identically-appearing placebo, with approximately 107 subjects per treatment group. This is a 113-week study. The subjects will spend 24 weeks in the double-blind, placebo-controlled treatment phase, followed by 28 weeks of active treatment phase (ie, up to Week 52 visit). The original treatment assignments (apremilast 30 mg BID (twice a day) or placebo) will remain blinded until all subjects have completed their Week 52 visit (or have discontinued). After the Week 52 visit, all subjects in the extension phase will continue to receive treatment with apremilast 30 mg BID (twice a day) until the end of the study (ie, up to Week 104 visit) or until early discontinuation from the trial. The study will consist of 5 phases: 1. Screening Phase - up to 5 weeks 2. Randomized, Placebo-controlled, Double Blind Treatment Phase - Weeks 0 to 24 3. Active Treatment Phase - Week 24 to Week 52 4. Open-label Extension Phase - Week 52 to Week 104 5. Post-treatment Observational Follow-up Phase