Avanafil Stendra. Vardenafil usually works for 4 to 5 hours. Do not use any other medicine to treat impotence unless your doctor tells you to. Vardenafil is taken only when needed, about 60 minutes before sexual activity. Sildenafil Viagra. This medication is taken with or without food an hour before sex.Levitra is not a cure for ED and you still need to be aroused for the medication to work. Levitra and its generic version are available in doses of: . Follow the directions on the prescription label. You may take this medication with or without meals. The dose is usually taken 1 hour before sexual activity. You should not . Viagra, Cialis, Levitra, and Stendra are oral medications used to treat erectile dysfunction (ED). You may also know them by their generic names: sildenafil .