Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. Use the oral syringe provided with your medication to measure and take your dose. Sorry something went wrong with your subscription Please, try again in a couple of minutes Retry. Sildenafil usually should not be taken more than once every 24 hours. Different brands may not work the same way. If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food.Generic: Sildenafil. Form: oral tablet; Strengths: 25 mg, 50 mg, mg; Brand: Viagra. Form: oral tablet; Strengths: 25 mg, 50 mg, mg; Adult dosage (ages 18–64 years). mg; Like Viagra, certain forms of sildenafil are approved to treat ED in males* ages 18 years and older. For example, sildenafil mg, mg, and mg tablets are . Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial .