The first-in-class PDE4 inhibitor, oral roflumilast (Daliresp®, Daxas®), was approved by the U.S. Food and Drug Administration in 2011 to reduce the risk of COPD exacerbations in patients with severe COPD associated with chronic bronchitis and a history of exacerbations (U.S. Food and Drug Administration, 2013). Here, PDE4A is linked to chronic obstructive pulmonary disease.