Three types of medications are used to produce an erection: phentolamine, papaverine, and prostaglandin E1. Both phentolamine and prostaglandin E1 work by interfering with alpha nerves that cause the penis to remain in a limp state. By blocking these nerves, an unrestrained flow of blood reaches the penis and makes it ready for intercourse.

The exact mechanism of papaverine is unknown but it supposedly causes intrapenile smooth muscles to relax, thereby allowing increased blood flow to the penis.

The injections are not as bad as they sound. Patients can learn to administer them from their urologists. A very small needle is used and only a small amount of the medication is necessary. Pain is minimal.

To be effective, the injections must be made at a specific site at the side of the penis. Erection occurs within 10 to 30 minutes and can last for several hours.

The success rate of penile injection therapy varies depending on the medications used. For prostaglandin E1, it can reach as high as 86 percent as one Japanese study reported. However, not one medication is ideal and not everyone is satisfied with this treatment.

"Different doses of drugs have been administered. Doses effective in inducing the first erection are not consistently effective in maintaining satisfactory erections with each successive injection. A need to increase the dose after a while or switch from one medication to another seems to be the standard. Even men who have a fully satisfactory response do not always stay with this form of treatment; about one-third drop out," according to Dr. Richard F. Spark, associate clinical professor of medicine at Harvard Medical School in Male Sexual Health: A Couple's Guide.

But there are some problems associated with penile injection therapy. Men who use phentolamine and/or papaverine, for instance, develop nodules and scarring within the penis. There is also the risk of infection, pain, and bruises.

"It was originally believed that papaverine or papaverine/phentolamine injected directly into the penis would remain there and not enter the bloodstream. This has proved not to be the case. Some of the mixture enters the general circulation and causes damage to the liver. Up to 40 percent of men who continue long term treatment can expect to develop at least one abnormality of liver function: mild inflammation," Spark revealed.

Another problem is priapism or prolonged painful erections that can last for six to 12 hours if higher doses are used. This can be so severe to the point that penile tissue is destroyed and surgery may be the only way out.

"In our study, 486 patients used papaverine. Sometimes the erections would begin normally but it would persist for up to 24 hours. For the first two hours, the wife would have a fantastic time. But more than that, she would complain and it became painful for the man. In 10 percent of patients, there was scarring at the site of injection," said Dr. Edward John Keogh, medical director of the Reproductive Medicine Research Institute at Queen Elizabeth II Medical Center in Nedlands, western Australia.

There seems to be fewer problems with prostaglandin E1 but its long-term effects are unknown. Because of this, the drug of choice for intrapenile injection therapy has yet to be found.

In spite of this, over 60,000 injections have been given to over 30,000 men in the United States, Japan and Europe. Hopefully, more men will avail of this treatment as more information regarding penile injection surfaces in the next few years. For those with severe vascular disease or in diabetics over 60, however, prostaglandin E1 injections won't work.

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