Health

FDA okays snail-inspired painkiller

WASHINGTON - A synthetic form of a sea-snail venom was approved Tuesday 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 an entirely 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 now 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 like OxyContin and morphine. Ultimately they may also provide an alternative for severely affected patients dependent on medications such as Celebrex, Aleve and now-recalled Vioxx that have come under fire because of indications they may cause heart problems.

"This drug is very exciting because it's a very potent analgesic but isn't a narcotic," said Richard 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 Tuesday'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 must be delivered directly into the fluid surrounding 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 up to 100,000 people in the United States might be helped.

About 50,000 patients already have implanted or external devices that pump morphine directly into the spinal column, he said, and many of them may want to try Prialt because opioids can gradually lose their effectiveness. In addition, many patients in severe pain who take pain pills may try the spinal cord route if the drug involved is not an opioid, he said.

Prialt is a synthetic form of the venom that the Conus magus, which lives in tropical saltwater shallows, uses to stun prey.

Prialt, expected to reach the market next month, will come with a black box warning regarding its risks, which include hallucinations and even psychosis in vulnerable people.

Despite Prialt's limitations, Mary Pat Aardrup, executive director of the National Pain Foundation, a nonprofit education group, called Tuesday a "red-letter day" for pain patients.

"To have another pain drug in an entirely new class is very exciting and very hopeful."

NEW APPROACH: The drug, known chemically as ziconotide, is part of a new class of drugs known as N-type calcium channel blockers. It selectively blocks nerve channels that transmit pain signals. It's dripped into the spine.

LIKE A SNAIL: A snail called the Conus magus that lives in the South Pacific paralyzes its victims with venom after capturing them. Researchers copied the venom's amino acid sequence.

WHO IT BENEFITS: The 50,000 to 100,000 people in the United States with severe pain who only had the option of opioids like morphine that gradually lose effectiveness.

SIDE EFFECTS: Include dizziness, drowsiness and altered mental status, with patients confused at times.

WHEN IT WILL BE AVAILABLE: By the end of January.

-SOURCES: Associated Press, Washington Post

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