Take sildenafil exactly as directed. Tell your doctor if any of these symptoms are severe or do not go away: headache. Click here for an email preview. Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. Ask your pharmacist for a list of the ingredients. Take sildenafil as needed before sexual activity.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 . By Ginger Skinner Last updated: June 14, If you’re looking for a less costly Viagra, you might want to ask your doctor about sildenafil. It’s the active . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual .