Children 1 year of age and older weighing 45 kilograms kg or more—20 mg 3 times a day. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. Dosing The dose of this medicine will be different for different patients. Before starting, stopping, or changing any medications while taking sildenafil, please get the advice of your doctor or pharmacist.Take sildenafil as needed before sexual activity. 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 . What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with . CHOOSE BRAND-NAME VIAGRA. The original little blue pill prescribed by doctors for over 20 years. Clinically proven to treat men with erectile dysfunction (ED) Ongoing .