Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Children 1 year of age and older weighing 45 kilograms kg or more—20 mg 3 times a day. There are no adequate and well-controlled studies of sildenafil in pregnant women. You may take this medicine with or without food. In this case, just leave out the missed dose and take your next dose at the usual time. · Viagra® also contains sildenafil. If you take too much sildenafil or take it together with these medicines, the chance for side effects will be higher. Sildenafil should not be used with any other medicine or device that causes erections. It is important to tell your doctor about any heart problems you have now or may have had in the past. This means that 4 hours after you take a dose, your body has cleared half of the dose. In most cases, it takes about 5 half-lives for your body to completely remove a drug from your system. So. 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 .