These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. Do not mix the liquid with other medications or add anything to flavor the medication. What special dietary instructions should I follow? Side effects Side effects of oral ED medicines are often mild. Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse.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 . Sildenafil is a prescription drug. It comes in the form of a tablet and suspension (liquid). Both are taken by mouth. It also comes in an intravenous (IV) form, . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes .