Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking sildenafil. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Tell your doctor if any of these symptoms are severe or do not go away: headache. How should this medicine be used? Sildenafil Viagra is used to treat erectile dysfunction impotence; inability to get or keep an erection in men. Use the oral syringe provided with your medication to measure and take your dose. 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 lungs, causing shortness of breath, dizziness, and tiredness.While generic sildenafil and Viagra are equally safe and effective, the medications have one key difference: price. Viagra costs around $60–$70 per tablet. Viagra costs around $60–$70 per tablet. Here are some details on sildenafil: Drug class: phosphodiesterase type 5 (PDE5) inhibitor Drug forms: oral tablet, liquid suspension, intravenous (IV) bolus . This means that 4 hours after you take a dose, your body has cleared half of the dose. In most cases, it takes about 5 half-lives for your body to completely remove a drug from your system. So.