Psoriatic arthritis (PsA) is a chronic inflammatory disease of the joints that 
occurs in patients with psoriasis. The spectrum of PsA includes arthritis, 
dactylitis, enthesitis, axial involvement, and skin lesions. Non-biologic 
disease-modifying anti-rheumatic drugs (DMARDs) such as methotrexate and 
leflunomide, and biologic DMARDs such as tumor necrosis factor (TNF) antagonists 
and ustekinumab, have been used to treat PsA. Apremilast is a novel therapy that 
inhibits phosphodiesterase 4, increases intracellular cAMP levels, and modulates 
expression of inflammatory mediators in favor of anti-inflammatory activity. It 
decreases the pro-inflammatory cytokines TNF-α, IFN-γ, IL-17, and IL-23 and 
increases the anti-inflammatory cytokine IL-10 under certain conditions. One 
phase II and four phase III clinical trials as well as long-term extension 
studies showed significant and sustained clinical efficacy and an adequate 
safety profile for apremilast in patients with active psoriatic arthritis.