TUESDAY, Jan. 6 (HealthDayNews) -- A novel, non-addictive drug derived from the venom of a marine snail provides significant relief for cancer and AIDS patients who suffer from intractable pain.

Results of a new study indicate that more than half of these patients who don't respond to other painkillers found relief when they were given the drug, called ziconotide.

Ziconotide is made of venom from the cone snail, which uses the toxin to immobilize both predators and prey. Scientists have warned the cone snail is fast becoming a threatened species because of pollution, overfishing, development and the exploitation of its beautiful shells. They fear the species could disappear before biomedical research can take full advantage of the analgesic properties of the venom.

Ziconotide is an entirely new, non-narcotic pain medication that is 1,000 times more potent than morphine without the problems of addiction or withdrawal. It works by blocking the N-type, neuron-specific, voltage-sensitive calcium channels, which are found at presynaptic nerve terminals.

A team led by Dr. Michael G. Byas-Smith, an assistant professor of anesthesiology at Emory University Medical School, treated 111 patients with cancer or AIDS who had failed to find relief with other pain medications. The patients were randomly assigned to receive ziconotide or a placebo. Most of the patients were taking morphine at the start of the study. Ziconotide was given continuously through a pump that delivers a measured dose.

The researchers found 53 percent of the patients receiving ziconotide had moderate to complete pain relief, compared with 17.5 percent of the patients receiving the placebo. In addition, five of the patients in the ziconotide group had complete relief from pain. The findings appear in the Jan. 7 issue of the Journal of the American Medical Association.

The drawbacks to ziconotide are the side effects, which occur when high doses are given, Byas-Smith says. The most common was an altered mental state, but other side effects include low blood pressure and dizziness.

Patients who have severe pain from AIDS or cancer, and who do not get good relief with morphine, can use ziconotide alone or in combination with morphine and achieve better pain management, he adds.

Ziconotide, Byas-Smith notes, seems to be most effective in relieving neuropathic pain, which does not respond well to morphine. "Typically, you have to use an opiate and ziconotide to get the best pain relief," he says.

"We have another weapon to control pain. But it remains an ongoing process to figure out who is going to respond best to this treatment," Byas-Smith says.

Dr. Michel Y. Dubois, a professor of anesthesiology at New York University School of Medicine and director of the NYU Pain Center, says ziconotide "is not the magic bullet."

Dubois notes that in his study with patients who had pain from other nonmalignant problems, the results were similar, with about half responding, and no one knows why. "When it works, the relief does last," he adds.

"Unfortunately, it's not as spectacular as we expected it to be. However, ziconotide does have a place in some patients who have uncontrolled pain from cancer and AIDS," Dubois says. "But it is not going to revolutionize pain management."

Dr. Michael S. Leong, an assistant professor of anesthesia at Stanford University Medical Center, adds that his experience indicates that ziconotide can provide significant benefit for all types of intractable pain, including back pain, neck pain and other neuropathic pain.

In some cases, ziconotide may be more effective then morphine, he adds. However, ziconotide is expensive and difficult to administer and monitor, so its use will probably be limited.

Leong notes that trials using a combination of ziconotide and morphine are almost complete. He believes that when these drugs are used in combination, more patients will respond. Also, lower doses of each drug will be needed, thus reducing side effects.

Physicians are still learning how best to use ziconotide, he says.

More information

To learn more about pain management, visit the National Foundation for the Treatment of Pain or the American Pain Foundation.



SOURCES: Michael G. Byas-Smith, M.D., assistant professor, anesthesiology, Emory University Medical School, Atlanta; Michel Y. Dubois, M.D., professor, anesthesiology, New York University School of Medicine, and director, NYU Pain Center, New York City; Michael S. Leong, M.D., assistant professor, anesthesia, Stanford University Medical Center, Palo Alto, Calif.; Jan. 7, 2004, Journal of the American Medical Association

Last Updated: Jan-06-2004