In the United States alone, it is estimated that more than 30 million Americans assigned male at birth experience ED. Do not keep outdated medicine or medicine no longer needed. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco. Other prescription medications in the PDE-5 inhibitor class besides Viagra include the following: Generic vardenafil is similar to Viagra and may last up to five hours.Taking Viagra one hour before sexual activity is recommended for most people, but you can take it anywhere from 30 minutes to four hours prior. Maximum drug concentration, . Appropriate studies have not been performed on the relationship of age to the effects of sildenafil in children younger than 1 year of age. Safety and efficacy have not been . The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take .