PDE4A and asthma: Ensifentrine is included in this review as it is characterized in the literature as dual PDE3 and PDE4 inhibitor, but it is recognized that no reliable evidence is available for its ability to elicit PDE4 inhibitor like anti-inflammatory activity in patients with COPD or asthma (Cazzola et al., 2019) and most of the clinical effects of ensifentrine are likely attributable to PDE3 inhibition alone.