Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Take sildenafil at around the same times every day. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. Precautions It is important that you tell all of your doctors that you take sildenafil. Leukemia blood related cancer or Multiple myeloma blood related cancer or Sickle-cell anemia blood disorder —Sildenafil should be used with caution in these patients as problems with prolonged erection of the penis may occur. Do not stop taking sildenafil without talking to your doctor.Sildenafil is a generic drug, which is an exact copy of the active drug in a brand-name medication. The generic is considered to be as safe and effective as the original drug. And generics tend to. Priapism warning: This drug can cause priapism, which is an erection that won’t go away. If you have an erection that lasts more than 4 hours, call or go to the nearest emergency room. If it. Generic Names: Sildenafil Citrate Brand Names: Revatio Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Learn more about .