The onset of action can occur within 30 minutes, while the duration of the effect can last up to 18 hours. Children 1 year of age and older weighing 20 to 45 kg—20 mg 3 times a day. However, the dose is usually not more than 80 mg 3 times a day. May make this condition worse. If you already use medicine for high blood pressure hypertension , sildenafil could make your blood pressure go too low. This medicine can cause serious side effects in patients with heart problems. Dosage and strength for pulmonary hypertension Sildenafil tablets for pulmonary hypertension come in 10mg and 20mg strengths. · Maintenance: 25 to mg orally once a day, as needed, 1 hour prior to sexual activity Comments: This drug may be taken anywhere from 30 minutes to 4 hours before sexual activity. Use: Treatment of erectile dysfunction. Usual Adult Dose for Pulmonary Hypertension. Revatio (R): Oral: Initial dose: 5 or 20 mg orally three times a .  · Sildenafil is used to treat erectile dysfunction and pulmonary arterial hypertension. Includes sildenafil side effects, interactions and indications. The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). To access savings, use a GoodRx coupon and pay just a fraction of the retail price. Viagra (brand) .