PDE4A and chronic obstructive pulmonary disease: Among the most important trials identified in the current search is a phase 3 multicenter trial comparing roflumilast to the antimicrobial azithromycin as prevention of COPD exacerbations (NCT04069312) and a comparison of roflumilast to the inhaled PDE4 inhibitor tanimilast as maintenance therapy in COPD (NCT04636814; for further discussion of the pre-clinical and early-stage development of tanimilast and ensifentrine, see a prior review [9]).