In patients with vasoactive pulmonary arterial hypertension, vasodilation of the pulmonary artery leads to reduced resistance to blood flow, with subsequent reductions in mean pulmonary arterial pressure. This medicine works best when you take it on an empty stomach an hour before sex. Some people may also have ringing in their ears tinnitus or dizziness. Deaths were first reported after approximately one year of use, and hence sildenafil, particularly chronic use, is not recommended in pediatric patients with PAH. However, the addition of sildenafil to bosentan therapy did not result in any improvement in exercise capacity. It might work longer if you have mild to moderate erectile dysfunction.– starting at $2 per dose of sildenafil, depending on dosage: 20 mg: Optum Store: yes: yes – starting at $80 per dose of Viagra 20– mg: REX MD: yes: yes – $90 per dose of Viagra. Typical dosage: 5 or 20 mg, taken three times per day about 4 to 6 hours apart Maximum dosage: 20 mg, taken three times per day about 4 to 6 hours apart Child dosage (ages 0–17 years). 20 mg sildenafil oral tablet from $ for 10 tablets 25 mg sildenafil oral tablet from $ for 30 tablets 50 mg sildenafil oral tablet from $ for 15 tablets mg .