The concomitant use of erythromycin or strong CYP3A4 inhibitors e. 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. VIAGRA was administered to more than 3, patients aged 19 to 87 years, with ED of various etiologies organic, psychogenic, mixed with a mean duration of 5 years. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. It continues to work for up to 4 hours, although its action is usually less after 2 hours. It is not known if the medicine is safe for use in these patients. Use the oral syringe provided with your medication to measure and take your dose.Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision. Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in is also used to treat pulmonary arterial hypertension, a serious heart and lung drug is more popular than comparable drugs. It is available in generic and brand versions. Generic sildenafil is covered by most Medicare and insurance plans, but . 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 .