PDE4A and chronic obstructive pulmonary disease: Tanimilast was about 10- and 900-fold more potent than roflumilast and cilomilast, respectively, in inhibiting PDE4 enzymatic activity (IC50 = 0.026 ± 0.006 nM), with the latter being a discontinued orally active PDE4 inhibitor developed up to Phase 3 in COPD (Giembycz, 2006).