O-Demethyl apremilast is an active metabolite of the phosphodiesterase 4 (PDE4) inhibitor apremilast .1It inhibits the activity of PDE4 isolated from U937 cells and LPS-induced TNF-α production in isolated human peripheral blood mononuclear cells (PBMCs; IC50s = 8.3 and 5.6 μM, respectively). O-Demethyl apremilast is also an oxidative degradation product of apremilast.2,3