In vitro studies have shown that vardenafil is more potent on PDE5 than on other known phosphodiesterases (> 15-fold relative to PDE6, > 130-fold relative to PDE1, > 300-fold relative to PDE11, and > 1000-fold relative to PDE2, PDE3, PDE4, PDE7, PDE8, PDE9 and PDE10).