Using this medicine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If you see air bubbles in the syringe, repeat the steps. John’s wort. The effects may be increased because of slower removal of the medicine from the body. Take sildenafil up to 4 hours before you want to have sex.Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the . Generic drugs usually cost less than the brand-name version. In some cases, they may not be available in every strength or form as the brand-name drug. Viagra (sildenafil citrate) tablets, for. Bookshelf ID: NBK PMID: Sildenafil is a medication used in the management and treatment of erectile dysfunction and pulmonary arterial hypertension. It is in the phosphodiesterase-5 inhibitor (PDE5-I) class of medications. This activity describes the indications, actions, adverse effects, and contraindications of .