Children 1 year of age and older weighing 45 kilograms kg or more—20 mg 3 times a day. Oral medicines for ED usually work well and cause few side effects. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food. You can take it in a small dose daily or in a larger dose as needed.They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction (ED). Oral medicines for ED usually work well and . 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 . VIAGRA contains sildenafil, which is the same medicine found in another drug called REVATIO. REVATIO is used to treat a rare disease called pulmonary arterial .