PDE4A and COVID-19: Phosphodiesterase-4 (PDE4) inhibitors have been advocated as potential repurposed agents for the treatment of early phase COVID-19 patients or as prophylaxis for the elderly admitted to resident care facilities [91,92,93], given their multiple anti-inflammatory activities (including inhibition of interleukin-17, closely involved in ALI caused by COVID-19 [94]) coupled with a well-known excellent safety profile [92,93].