However, it stays in your body for up to 36 hours and can be taken every 24 hours, so it can work for you constantly. Based upon measurements of sildenafil in semen of healthy volunteers 90 minutes after dosing, less than 0. The information provided is for educational purposes only and is not intended to replace discussions with a healthcare provider. You need a prescription from a doctor to obtain sildenafil. Similar values for pharmacokinetic parameters were seen in normal volunteers and in the patient population, using a population pharmacokinetic approach.Sildenafil Citrate Coupons, Prices, and Savings Card Brand Names: Revatio, Viagra Sildenafil is used to treat male sexual function problems (impotence or erectile . Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work. VIAGRA is supplied as blue, film-coated, rounded-diamond-shaped tablets containing sildenafil citrate equivalent to 25 mg, 50 mg, or mg of sildenafil. Tablets are debossed with PFIZER on one side and VGR25, VGR50 or VGR on the other to indicate the dosage strengths. Close.