AdNeed Safe and Affordable Medicine? is here to help you!Dosing The dose of this medicine will be different for different patients. Side effects Side effects of oral ED medicines are often mild. Take sildenafil as needed before sexual activity. There is a problem with information submitted for this request. If too much is used, the chance of side effects is increased. · Initial dose: 5 or 20 mg orally three times a day, 4 to 6 hours apart. Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. AdNeed Safe and Affordable Medicine? is here to help you! Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to mg. The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex.Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking sildenafil. Sildenafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. Children younger than 1 year of age—Use and dose must be determined by your doctor. Medicines that block an enzyme called CYP3A4. Sildenafil Viagra.