Alprostadil injection and suppositories are used to treat certain types of erectile dysfunction (impotence; inability to get or keep an erection) in men. Alprostadil injection is also sometimes used in combination with other tests to diagnose erectile dysfunction. Alprostadil is in a class of medications called vasodilators. It works by relaxing the muscles and blood vessels in the penis to keep enough blood in the penis so that an erection can occur.
Summary from MedlinePlus.gov, click for more information.