Brand names Why is this medication prescribed? Seven of these companies are based in India. This site is intended only for U. If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes. What special precautions should I follow?Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes Missing: sample.  · Brand names: Revatio, Viagra Drug classes: Agents for pulmonary hypertension, Impotence agents. Medically reviewed by Kaci Durbin, MD. Last updated . 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 .