If you have an erection that lasts more than 4 hours, get medical help right away. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly. If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction. Kidney disease that needs to be treated with dialysis. Vardenafil usually works for 4 to 5 hours. 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.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes . 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 . Know what to ask for Why should I ask for brand name VIAGRA? Who invented VIAGRA? Brand name vs. generic: what’s the difference? Know what’s available to you My .