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What is Alprostadil is not used for treatment of: and explain in detail?
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