 This lower selectivity is thought to be the basis for abnormalities related to color vision observed with higher doses or plasma levels.Vardenafil (marketed as Levitra, Staxyn and Vivanza) was the second oral PDE-5 inhibitor for erectile dysfunction to be FDA approved in August 2003.Tadalafil (marketed as Cialis) is a PDE5 inhibitor commonly that, in addition to its use in erectile dysfunction  is also used to treat pulmonary arterial hypertension.