Oral Erectile dysfunction Adult: 50 mg about 1 hr before sexual intercourse. May adjust dose depending on penile response. Max: 100 mg/dose and not to be taken > once in 24 hr. Elderly: >65 yr: Lower initial dose at 25 mg. Hepatic impairment: Initially, 25 mg. Pulmonary Arterial Hypertension 20 mg 3 times daily, administered 4-6 hours apart