Using alcohol or tobacco with certain medicines may also cause interactions to occur. If you experience a sudden loss of vision in one or both eyes, contact your doctor immediately. Take sildenafil up to 4 hours before you want to have sex. Remove the cap by pushing it down and twisting it counter-clockwise. Other contraindications include hypersensitivity to any component of the formulation, pulmonary veno-occlusion, left ventricular outflow obstruction, PAH associated with sickle cell anemia, and multiple system atrophy.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 . The cost for sildenafil oral tablet mg is around $10 for a supply of 2 tablets, depending on the pharmacy you visit. Quoted prices are for cash-paying customers and are not .  · The effects may be increased because of slower removal of the medicine from the body. 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.