The drug is almost totally metabolized within the intracavernous tissue. It had been used for peripheral vascular disease long before being applied to penile injection therapy. Alprostadil is the synthetic form of a naturally occurring unsaturated fatty acid that causes smooth muscle relaxation and vasodilation. The benefit, of course, is the reduction of unwanted side effects that may occur more often than with papaverine alone. Whereas, a 10 cc bottle of papaverine can be purchased for less than $20, the addition of Regitine increases the cost fourfold, up to $80 to $90 a bottle. Another major disadvantage to Caverject has been its cost. Up to 80 percent of patients, unfortunately, have pain at the injection site or during erection, while less than 2 percent had problems with prolonged erection and priapism. Several studies indicated that it was slightly more effective than papaverine alone, but about the same level of effectiveness as the combination of papaverine plus Regitine. Caverject was the first drug approved by the FDA for treating erectile dysfunction.

Since its first report of being safe and effective for home injection therapy in 1988, it has gained a wide acceptance. Caverject, a freeze-dried (lyophilized) powder, was specifically developed for intracavernous injection. Several formulations of alprostadil have been produced. This minimizes the incidence of prolonged systemic side effects. In most patients with veno-occlusive dysfunction the alprostadil level may rise to ten times baseline, but up to 90 percent of the drug is metabolized on the first pass through the lungs. No change in peripheral blood levels has been observed.