Fear of intimacy and anxiety about sexual performance can affect your ability to get and maintain an erection. According to a study by researchers for the International Society for Sexual Medicine, erectile dysfunction can see rates as high as These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. This medicine works best when you take it on an empty stomach an hour before sex. Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. That means they can increase the amount of Viagra in your body, which can cause unwanted side effects.For treatment of erectile dysfunction: For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual . They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction (ED). Oral medicines for ED usually work well and cause few side . You should not use Viagra if you are allergic to sildenafil, or: if you take other medicines to treat pulmonary arterial hypertension, such as riociguat (Adempas). if you take nitrates. .