Viagra Works for the Long Haul

Oct. 21, 2003 (Salt Lake City) -- With prostate cancer treatment success often comes at a heavy price: erectile dysfunction. But, a new study shows that Viagra will work in nearly 70% of the men who have radiation-associated erectile dysfunction for years to come.

Michael Zelefsky, MD, of Memorial Sloan-Kettering Cancer Center, N.Y., tells WebMD that the radiation-associated erectile dysfunction usually "begins about six months after [they] have concluded therapy, but it can occur at any time during or after treatment." He says that he has already reported that "about 70% of men initially respond to Viagra. However, [they] didn't know if the response would be durable."

In the new study, which was presented at the 45^th Annual Meeting of the American Society for Therapeutic Radiology and Oncology, Zelefsky and his colleagues studied the "durability" of response by following 360 men with radiation-induced erectile dysfunction who initially responded to the drug. He followed the group for an average of nearly four years after their surgery to see if they were still taking Viagra for erectile dysfunction.

The results, he says, were surprising. "I didn't really expect them to still be taking the drug and I expected that for many men the effect would diminish with time." But after almost four years, 96% of the men who initially responded to Viagra were still taking the drug and all but six of those men said the drug was still effective.

All of the men in the study had prostate cancer that was confined to the prostate gland. They received radiation therapy by either external beam treatment or by brachytherapy, in which radioactive "seeds" implanted in the prostate deliver radiation directly to the tumor.

The external radiation is done while the patient lies in a special box that allows multiple radiation beams to be directed directly to the prostate gland from all sides, while the rest of the body is protected from the radiation.

Prostate cancer is mainly found in older men. After prostate cancer has been diagnosed, tests are done to determine if it has spread outside the gland. Because there are different treatments available, determining how much the cancer has spread this will help in deciding what treatment is best for the cancer.

Surgery to remove the cancer is one option that is used to treat prostate cancer. Radiation is another therapy used in treating this cancer. Erectile dysfunction can occur in men treated with either one of these treatments.

Zelefsky says the men who reported that Viagra stopped working were those who were treated with extremely high-dose external radiation.

Richard Valicenti, MD, associate professor radiation oncology, at Thomas Jefferson University Hospital, in Philadelphia, tells WebMD that the study is "important since it shows that treatment with [Viagra] can deliver a durable response." But Valicenti, who wasn't involved in the study, says that he, too, is a little surprised by the results, especially because of the fairly large range in the length of treatment and because drug tolerance is common.

"We don't really know how often they are taking the drug. We know that with repeated use tolerance develops for many drugs and we expect it for this drug as well," he says.

If tolerance does develop, the new erectile dysfunction drug, Levitra, could be an option says Zelefsky. He says his group is conducting a study with this newly approved drug but notes that it will be sometime before the results are available. Meanwhile, he says that he is trying Levitra in men who don't initially respond to Viagra.