Vardenafil usually works for 4 to 5 hours. This works in a similar way to Viagra , but its effects last for longer. Generic versions of sildenafil, vardenafil and tadalafil are available. The lower dose, meanwhile, is for those who have not tolerated the higher doses well. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. And Viagra is no exception.The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called . Learn about sildenafil (Viagra) usage and dosing. Read the latest news and reviews about the drug as well as potential side effects and popular alternatives. Viagra for Erectile Dysfunction User Reviews. Viagra has an average rating of out of 10 from a total of reviews for the treatment of Erectile Dysfunction. 82% of reviewers .