Alprostadil is not used for treatment of:
Erectile dysfunction
Pulmonary hypertension
Patent ductus arteriosus
Critical limb ischemia
To maintain patency of ductus arteriosus in neonates with congenital heart defects, till corrective surgery is undertaken, PGE1 (Alprostadil) is used.
Impotence: Alprostadil (PGE1) injected into the penis causes erection lasting 1-2 hours. However, oral sildenafil / tadalafil is now preferred for erectile dysfunction. 
Peripheral vascular diseases: PGI2 (or PGE1) infused i.v. can relieve rest pain and promote healing of ischaemic ulcers in severe cases of intermittent claudication and in Raynaud's disease.
Pulmonary hypertension: PGI2 lowers pulmonary artery resistance. Accordingly, few cases of primary pulmonary hypertension have been successfully maintained on epoprostenol infused continuously in a large vein.
lndomethacin  has been the most common drug used for medical closure of patent ductus arteriosus.

Reference: Essentials of Medical Pharmacology Eighth Edition KD TRIPATHI page no 207,219