If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule. Dosing The dose of this medicine will be different for different patients. Medicines that you take by mouth are called oral medicines. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. It continues to work for up to 4 hours, although its action is usually less after 2 hours.In combination with sexual stimulation, sildenafil works by increasing blood flow to the penis to help a man get and keep an test1.ru drug does not protect against . Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in . RESOURCES GETTING STARTED WITH VIAGRA Your doctor has determined that VIAGRA may be right for you. Follow his or her instructions carefully to help you get the .