It continues to work for up to 4 hours, although its action is usually less after 2 hours. Especially tell your healthcare provider if you take any of the following: medicines called nitrates medicines called guanylate cyclase stimulators such as Adempas riociguat medicines called alpha-blockers, such as Hytrin terazosin HCl , Flomax tamsulosin HCl , Cardura doxazosin mesylate , Minipress prazosin HCl , Uroxatral alfuzosin HCl , Jalyn dutasteride and tamsulosin HCl , or Rapaflo silodosin. Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. Place the tip of the syringe into you or your child’s mouth and point it towards the cheek. Ask your healthcare professional how you should dispose of any medicine you do not use.Viagra or generic sildenafil for ED should not be used in women. Dosage for erectile dysfunction (ED) Generic: Sildenafil. Form: oral tablet; Strengths: 25 mg, 50 mg, mg; Brand: Viagra. · Dosing For treatment of erectile dysfunction: For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a Adults up to 65 years of age—50 milligrams (mg) as. · What is sildenafil? Sildenafil relaxes muscles of the blood vessels and increases blood flow to particular areas of the body. Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men.