They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. These medicines are called PDE5 inhibitors. Sildenafil Viagra. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED.CHOOSE BRAND-NAME VIAGRA The original little blue pill prescribed by doctors for over 20 years Clinically proven to treat men with erectile dysfunction (ED) Ongoing . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or . · Take sildenafil exactly as it was prescribed for you. Follow all directions on your prescription label and read all medication guides or instruction sheets. Revatio is .