If you become pregnant while taking sildenafil, call your doctor. Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. Do not use more of it and do not use it more often than your doctor ordered. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection.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 . 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 .  · Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken .