May make this condition worse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Kidney disease, severe or Liver disease, severe—Use with caution. John’s wort. Remove the syringe from the bottle. If too much is used, the chance of side effects is increased. Do not use this medicine if you are also using a nitrate medicine, often used to treat angina or high blood pressure.Generic Names: Sildenafil Citrate Brand Names: Revatio Sildenafil is used to treat male sexual function problems (impotence or erectile dysfunction-ED). Learn more about . Drug details Here are some details on sildenafil: Drug class: phosphodiesterase type 5 (PDE5) inhibitor Drug forms: oral tablet, liquid suspension, intravenous (IV) bolus injection Brand-name.  · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where this enzyme works.