Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss. VIAGRA sildenafil citrate is supplied as blue, film-coated, rounded-diamond-shaped tablets containing sildenafil citrate equivalent to the nominally indicated amount of sildenafil and debossed on the obverse and reverse sides as follows: 25 mg. It is eliminated predominantly by hepatic metabolism mainly CYP3A4 and is converted to an active metabolite with properties similar to the parent, sildenafil.from $ for 10 tablets 25 mg sildenafil oral tablet from $ for 30 tablets 50 mg sildenafil oral tablet from $ for 15 tablets mg sildenafil oral tablet from $ for . The average length of time Viagra lasts. On average, Viagra lasts between 2 and 3 hours before its effects start to diminish. Viagra can last up to 5 hours or longer depending on your dosage, your. 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.