Sildenafil is also sometimes used to treat pulmonary hypertension high blood pressure in the blood vessels that supply the lungs. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Population pharmacokinetic data from patients in clinical trials also indicated a reduction in sildenafil clearance when it was co-administered with CYP3A4 inhibitors such as ketoconazole, erythromycin, or cimetidine [see Dosage and Administration 2. Therefore, inhibitors of these isoenzymes may reduce sildenafil clearance and inducers of these isoenzymes may increase sildenafil clearance. At the same time, on-treatment function was better in treated patients who were less impaired at baseline.AdDon’t go to the pharmacy without checking prices at GoodRx® first. No commitment or fees. Find the lowest price in your neighborhood & use our free coupons to save up to 80%Service catalog: Prescription Coupons, Prescription Discounts, Online Doctor Visits. Find patient medical information for Viagra oral on MD including its uses, side effects and safety, interactions, pictures, warnings and user ratings. 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.