However, the dose is usually not more than 80 mg 3 times a day. What should I do if I forget a dose? Brand names Why is this medication prescribed? The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. Do not use this medicine if you are also using a nitrate medicine, often used to treat angina or high blood pressure. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it.Product (s) Viagra mg Tablets 4 (Repat Authority Script) – Sildenafil. Private Prescription Price. $ Discounted PBS Price. -. Concession PBS Price. $ Safety Net Price. According to price-comparison site test1.ru, generic Revatio will cost you as little as $ per pill, depending on where you fill your prescription. That’s compared with . 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 adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the .