Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Sildenafil comes as a tablet and suspension liquid to take by mouth. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. This medicine is available only with your doctor’s prescription. This is a type of high blood pressure that occurs between the heart and the lungs.Sildenafil oral tablet is available as a brand-name drug and as a generic drug. Brand names: Viagra, Revatio. Sildenafil comes in three forms: an oral tablet, an oral suspension (liquid).  · The highest recommended Viagra dose for treating erectile dysfunction (ED) is mg per day, according to the drug’s manufacturer. Doses of mg or mg would be considered off-label use. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men.