The main measure of effectiveness was based on the ability of the men to get and maintain an erection. Both sildenafil and the metabolite have terminal half lives of about 4 hours. Protein binding is independent of total drug concentrations. Sudden vision loss in one or both eyes can be a sign of a serious eye problem called non-arteritic anterior ischemic optic neuropathy NAION. If you become pregnant while taking sildenafil, call your doctor. Which Works Faster?Assessment history. Authorised. This medicine is authorised for use in the European Union. Overview. This is a summary of the European public assessment report (EPAR) for Viagra. The generic name for Viagra is sildenafil. The drug also has another brand name: Revatio. It works by slowing down the action of PDE5, an enzyme in the blood vessel walls.. This enzyme breaks down. 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 .