Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. If we combine this information with your protected health information, we will treat all of that information as protected health information and will only use or disclose that information as set forth in our notice of privacy practices. This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it.Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum . Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in men. It is also used to treat pulmonary arterial hypertension, a serious heart and lung .  · Proper Use Drug information provided by: Merative, Micromedex ® Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it more .