A synthetic form of a sea-snail venom was approved yesterday by the Food and Drug Administration as a novel approach to treating severe, chronic pain.
The drug, called Prialt, was approved for hard-to-treat pain associated with cancer, AIDS and neuropathies. Based on a compound found in the poison of the South Pacific cone snail, it controls pain in a new way -- by blocking the calcium channels in nerve cells that transmit pain signals -- and may have broad implications for the future of pain management.
Because it is as much as 1,000 times more powerful than morphine, it is considered a last resort for long-suffering patients, rather than a first-line pain medication. But the manufacturer, Elan Corp. of Ireland, hopes that will change.
Researchers believe the snail venom, and products like it, can become an alternative to opioid drugs such as OxyContin and morphine. Ultimately, it may also provide an alternative for severely affected patients dependent on medications such as Celebrex, Aleve and now-withdrawn Vioxx -- which have come under fire because of indications that they may cause heart problems.
"This drug is very exciting because it's a very potent analgesic but isn't a narcotic," said Richard L. Rauck of Wake Forest University medical center and the Carolinas Pain Institute. Rauck, an investigator for one of the Elan-funded clinical trials that led to yesterday's FDA approval, said he found the drug to be "effective in almost all types of chronic pain it's been studied in."
What will limit the use of Prialt, and other potential drugs derived from tree frogs and other creatures with natural venoms, is that it cannot be taken in pill form. It has to be delivered directly into the fluid that surrounds the spinal cord, which carries it to the brain without affecting other organs. Because it is so potent, tiny amounts of the drug could be dangerous to the heart and possibly other organs.
"This drug is for patients in chronic and severe pain who are not getting substantial and meaningful relief with oral opiates, or are having unacceptable side effects with them," said Robert Meyer, director of the FDA's Office of Drug Evaluation II. "At this point we don't see this class of drug expanding to general use."
Nonetheless, Elan's president for global research and development, Lars Ekman, said as many as 100,000 people in the United States might be helped by the drug.
He said about 50,000 patients have implanted or external devices that pump morphine directly into the spinal column, and many of them may want to try Prialt because opioids can gradually lose their effectiveness. In addition, he said, many patients in severe pain who take pain pills may want to try the spinal cord route if the drug involved is not an opioid.
"There are thousands of people out there who have pain like a bad toothache all day and night, week after week," Ekman said. "Many of these people have tried morphine and it either didn't work or made them unable to function."