Take sildenafil exactly as directed. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Brand names Why is this medication prescribed? Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. These medicines all work well for ED. The combination can cause a dangerous fall in your blood pressure.Sildenafil is used to treat erectile dysfunction (ED) and to reduce blood pressure in pulmonary arterial hypertension (PAH). It is taken when needed for ED and daily for PAH. A headache, stomach upsets, and flushing are the main side effects, and it should not be taken within 24 hours of a nitrate. 5. Tips.  · Maintenance: 25 to mg orally once a day, as needed, 1 hour prior to sexual activity Comments: This drug may be taken anywhere from 30 minutes to 4 hours before sexual activity. Use: Treatment of erectile dysfunction. Usual Adult Dose for Pulmonary Hypertension. Revatio (R): Oral: Initial dose: 5 or 20 mg orally three times a . Price without insurance: starts at $6 per dose for 10 doses. Doses: 20, 25, 50, and mg. Supply: 30, 90, or days. Sildenafil is the generic form of Viagra and Revatio. It’s chemically.