Over 80 percent of men who use injectable alprostadil to treat erectile dysfunction, or ED, experience an erection firm enough for intercourse within 20 minutes regardless of the reason for their ED, according to WebMD. Intercourse can occur 10 to 30 minutes after the injection, and the erection typically lasts for about an hour. Men should wait at least 24 hours between injections and are advised not to exceed three uses of alprostadil per week.
The prescription medication form of alprostadil is sold as Prostin VR, Caverject and Edex, reports WebMD. Because it causes a man’s blood vessels to expand, blood flow to the penis is increased, resulting in an erection. The most common side effect is pain at the injection site, but rare cases of testicular pain and swelling or painful erections lasting for longer than six hours are possible. Occasionally a man might experience a stinging in, or bleeding from, his urethra that requires immediate medical attention.
Some men treat ED with an injectable medication called Trimix that relaxes the smooth muscles in the penis, notes Memorial Sloan Kettering Cancer Center. This mixture of alprostadil, phentolamine and papaverine cannot be combined with any other ED drugs, including Viagra, Cialis and Levitra. A man usually finds the appropriate dose that allows him to experience erections consistently firm enough for intercourse by his sixth injection.