Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. In some cases, ED can cause a strain on relationships and impact self-esteem. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. Read our editorial process. Levitra vardenafil : This medication is taken one hour before sex and can last up to 24 hours.The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 . Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in . According to price-comparison site test1.ru, generic Revatio will cost you as little as $ per pill, depending on where you fill your prescription. That’s compared with .