PDE4A and chronic obstructive pulmonary disease: Tofimilast is a less potent (IC50 = 140 nM) inhaled PDE4 inhibitor [54] and has been found inefficacious in various clinical trials, i.e., in mild asthma [55], persistent asthma [56], GOLD stage II and III COPD patients, and LPS-challenged healthy subjects [57].