Take sildenafil as needed before sexual activity. Sildenafil usually should not be taken more than once every 24 hours. Do not drink grapefruit juice if you’re taking sildenafil Revatio for pulmonary hypertension. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. This medicine can interact with other medicines and supplements, causing potentially serious side effects. These patients had erectile dysfunction at baseline that was characterized by median categorical scores of 2 a few times on principal IIEF questions. Some medications should not be taken with sildenafil.Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be. 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. 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.