The use of prostacyclin analogues, endothelin receptor antagonists, and arginine supplementation were not permitted. Contraindications and cautions Do not prescribe a phosphodiesterase-5 PDE-5 inhibitor to a man with: Unstable angina or angina occurring during sexual intercourse. Children 1 year of age and older weighing 20 kg or less—10 mg 3 times a day. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. Sildenafil may cause side effects. Follow your doctor’s orders or the directions on the label. · Before taking this medicine. You should not use sildenafil if you are allergic to it, or: if you take other medicines to treat pulmonary arterial hypertension, such as . Sildenafil should be used with caution in men taking an alpha-blocker (especially doxazosin). Hypotension is more likely to occur within four hours following treatment with .  · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase .