Do not stop taking sildenafil without talking to your doctor. Which Is More Effective? Cialis can be taken daily, providing constant treatment for ED for people who have sex frequently. Different brands may not work the same way. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day.Sildenafil (Viagra) is a phosphodiesterase-5 (PDE-5) inhibitor. PDE-5 is a protein in your body that breaks down the molecules that normally cause an erection. When it blocks PDE-5, sildenafil (Viagra) helps an erection occur by allowing certain muscles in the penis to relax and the penis to fill with blood.  · Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Drug classes: Agents for pulmonary hypertension, Impotence agents Medically reviewed by Kaci Durbin, MD. Last updated on Uses Warnings Before taking Dosage Side effects Interactions FAQ What is sildenafil? The dose of Cialis you need will depend on whether you’re taking it daily or as needed. Daily doses are often between and 5 milligrams (mg). The as-needed dose is usually 10 mg but can range from 5–20 mg. The typicaldose of Viagra is 50 mg. However, the dosage can range from 25– mg.