PDE4A and chronic obstructive pulmonary disease: For example, an approach to COPD pharmacotherapy used by Spanish investigators utilizes an easy table of four major phenotypes (Non exacerbators, ACO, exacerbators with emphysema, exacerbators without emphysema) with five treatments options (bronchodilators, ICS, mucolytics, PDE4 inhibitors, macrolides), linking each of the four phenotypes with the appropriate treatment(s) [46].