For treatment of pulmonary arterial hypertension: For oral dosage forms suspension or tablets : Adults—20 milligrams mg 3 times a day. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. The penis is one of the areas where this enzyme works. It continues to work for up to 4 hours, although its action is usually less after 2 hours. There is a problem with information submitted for this request. Do not keep outdated medicine or medicine no longer needed.Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men.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 .  · This product is available in the following dosage forms: Tablet; Powder for Suspension; Suspension.  · Adults—20 milligrams (mg) 3 times a day. Your doctor may adjust your dose as needed and tolerated. However, the dose is usually not more than 80 mg 3 .