Sildenafil should not be used with any other medicine or device that causes erections. Read and follow these instructions carefully before you start using sildenafil and each time you get a refill of your medicine. Use the oral syringe provided with your medication to measure and take your dose. 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. Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss. · Viagra; Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where . Sildenafil oral tablet is available as a brand-name drug and as a generic drug. Brand names: Viagra, Revatio. Sildenafil comes in three forms: an oral tablet, an oral suspension (liquid), and an. 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.