PDE5A and erectile dysfunction: In contrast to dipyridamole, tadalafil (IC50 PDE5 inhibition: 1.8 nM), sildenafil (IC50 PDE5 inhibition: 5.22 nM), and vardenafil (IC50 PDE5 inhibition: 0.7 nM) have a high specificity in only inhibiting PDE5, and these compounds are used for the treatment of erectile dysfunction [5].