A PDE4 inhibitor (IC50 = 2 nM) and active metabolite of roflumilast; selective for PDE4 over PDE1-3 and PDE5 (IC50s = >10,000 nM for all); It reduces TNF-α-induced ICAM-1 and eotaxin levels when used in combination with PGE2 in GM06114 human fetal lung fibroblasts (IC50s = 0.9 and 0.5 nM, respectively); reverses cigarette smoke extract-induced reductions in ciliary beat frequency in isolated human bronchial epithelial cells at 2 nM; also increases plasma GLP-1 levels in a glucose challenge in diabetic db/db mice at 10 mg/kg, as well as prevents increases in blood glucose in db/db mice at 3 mg/kg per day