PDE4A and chronic obstructive pulmonary disease: As recently reviewed by Phillips (Phillips, 2020), at least four inhaled PDE4 inhibitors have progressed up to phase II, namely, AWD-12-281 (COPD and asthma), Tofimilast (COPD and asthma), UK-500,001 (COPD), GSK256066 (COPD and Asthma).