Fish toxin stops cancer pain

An experimental drug fashioned from the toxin of the puffer fish can suppress pain in cancer patients, a study shows.

Canadian researchers gave the toxin, called tetrodotoxin, by injection to 25 patients over 4 days. All the patients had failed to get relief from standard drugs. Nearly three-fourths of the patients said their pain was noticeably reduced during the tetrodotoxin test, and two patients reported complete relief at some times, says Neil Hagen of the University of Calgary in Alberta, who presented the findings in May at the North American Pain Conference in Vancouver, British Columbia.

The pain reduction generally kicked in after the second or third day of treatment and lasted several days beyond the last injection, Hagen notes. Two patients reported beneficial effects lasting more than 15 days.

Tetrodotoxin closes the pores that regulate the flow of sodium into nerve cells. However, exactly how the toxin stops pain remains a mystery.

Some of the patients reported mild, temporary side effects, including numbness, nausea, and a flushed feeling.

The toxin of the puffer fish, also called the blowfish, is potent. A single fish provides enough tetrodotoxin for roughly 600 doses of the pain medication, Hagen says.

A larger trial comparing the toxin-based medication to a placebo is getting under way. If proved effective, tetrodotoxin could offer an alternative to opiate-based drugs for pain, Hagen says.