Follow the manufacturer’s directions to use and clean the oral syringe. Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface. Using this medicine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. Do not keep outdated medicine or medicine no longer needed.Learn more about some of the side effects Viagra may cause. Low blood pressure. Available strengths: 25 mg, 50 mg, mg. Viagra comes in these . 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 .  · Revatio Viagra Descriptions Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines .