(5) Based on the above-mentioned different app-roaches to improve the therapeutic index, this review lays out future goals for research focused on the basis of efficacy and safety of PDE4 inhibitor combinations/FDC (Fixed-Dose Combination) and dual inhibitors of PDE3/4 as drugs for the treatment of patients with asthma or COPD. This evidence concerns the gene PDE4A and chronic obstructive pulmonary disease.