They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Do not take more or less of it or take it more often than prescribed by your doctor. These medicines are called PDE5 inhibitors. Children 1 year of age and older weighing 20 kg or less—10 mg 3 times a day. Do not mix the liquid with other medications or add anything to flavor the medication. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it.Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). Written by Brian Leonard, PharmD, BCACP, BCGP. Sildenafil Citrate Coupons, Prices, and Savings Card. Brand Names: Revatio, Viagra. Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Learn more about sildenafil oral. 1. Sildenafil is used to treat high blood pressure in the lungs (pulmonary hypertension).  · Maintenance: 25 to mg orally once a day, as needed, 1 hour prior to sexual activity Comments: This drug may be taken anywhere from 30 minutes to 4 hours before sexual activity. Use: Treatment of erectile dysfunction. Usual Adult Dose for Pulmonary Hypertension. Revatio (R): Oral: Initial dose: 5 or 20 mg orally three times a .