Apremilast, an oral phosphodiesterase 4 inhibitor, demonstrated effectiveness 
(versus placebo) for treatment of active psoriatic arthritis in the psoriatic 
arthritis long-term assessment of clinical efficacy (PALACE) phase III clinical 
trial program. Pharmacodynamic effects of apremilast on plasma biomarkers 
associated with inflammation were evaluated in a PALACE 1 substudy. Of 504 
patients randomized in PALACE 1, 150 (placebo: n = 51; apremilast 20 mg BID: n = 
51; apremilast 30 mg BID: n = 48) provided peripheral blood plasma samples for 
analysis in a multiplexed cytometric bead array assay measuring 47 proteins 
associated with systemic inflammatory immune responses. Association between 
biomarker levels and achievement of 20% improvement from baseline in modified 
American College of Rheumatology (ACR20) response criteria was assessed by 
logistic regression. At Week 24, IL-8, TNF-α, IL-6, MIP-1β, MCP-1, and ferritin 
were significantly reduced from baseline with apremilast 20 mg BID or 30 mg BID 
versus placebo. ACR20 response correlated with change in TNF-α level with both 
apremilast doses. At Week 40, IL-17, IL-23, IL-6, and ferritin were 
significantly decreased and IL-10 and IL-1 receptor antagonists significantly 
increased with apremilast 30 mg BID versus placebo. In patients with active 
psoriatic arthritis, apremilast reduced circulating levels of Th1 and Th17 
proinflammatory mediators and increased anti-inflammatory mediators.