Pediatric Patients: Increased mortality with increasing sildenafil dose was observed in a clinical trial of pediatric patients with PAH. This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it. Different brands may not work the same way. Never take 2 doses at the same time. Describe the clinically important drug interactions of sildenafil. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. · However, the dose is usually not more than 80 mg 3 times a day. Children 1 year of age and older weighing 45 kilograms (kg) or more—20 mg 3 times a day. Your doctor may adjust your dose as needed and tolerated. However the dose is usually not more than 40 mg 3 times a day. Children 1 year of age and older weighing 20 to 45 kg—20 . mg Like Viagra, certain forms of sildenafil are approved to treat ED in males* ages 18 years and older. For example, sildenafil mg, mg, and mg tablets are approved for this use. AdRead Customer Reviews & Find Best Sellers. Free, Easy Returns On Millions Of Items. Get Deals and Low Prices On sildenafil mg On has been visited by 1M+ users in the past month.