When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects. Its effects might last longer if you have mild to moderate ED. Follow your doctor’s orders or the directions on the label. Some people may also have ringing in their ears tinnitus or dizziness. Common ones include: Flushing of the skin. Vardenafil usually works for 4 to 5 hours. Kidney disease that needs to be treated with dialysis. · Viagra comes as an oral tablet that contains the active drug sildenafil. Sildenafil is also available in generic form. Viagra is classified as a phosphodiesterase type 5 (PDE5) inhibitor. For.  · Sildenafil (Oral Route) 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. Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with ED. With ED, you.