If you are a Mayo Clinic patient, this could include protected health information. Children 1 year of age and older weighing 20 kg or less—10 mg 3 times a day. What should I do if I forget a dose? 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. For treatment of pulmonary arterial hypertension: For oral dosage forms suspension or tablets : Adults—20 milligrams mg 3 times a day. Use the oral syringe provided with your medication to measure and take your dose. The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St. · Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Your doctor may adjust your dose if needed. Children—Use is not recommended. For treatment of pulmonary arterial hypertension.  · Sildenafil Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Drug classes: Agents for pulmonary hypertension, Impotence agents Medically reviewed by Kaci Durbin, MD. Last updated on Uses Warnings Before taking Dosage Side effects Interactions FAQ What is sildenafil? Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). In combination with sexual stimulation, sildenafil works by increasing blood flow to the penis.