Researchers Develop Lasting Anesthetic

Researchers at the Harvard-affiliated Children’s Hospital Boston have developed a long–lasting nerve block that could aid in the treatment of pain for patients undergoing surgery or experiencing chronic pain.

The anesthetic can be injected locally without causing nerve and muscle toxicity, according to Hila Epstein-Barash, the lead author of the paper and a research fellow.

“One of the main limitations to developments of these technologies previously was getting bad tissue reactions—nerve and muscle injuries,” said Daniel S. Kohane, one of the senior authors and an associate professor of anesthesia at Harvard Medical School. “The compounds we use tend to have little or no direct neurotoxic or muscle-toxic effects.”

The researchers packaged various combinations of compounds into liposomes—fat-and-lipid based particles found in cells—and injected the slow release anesthetic drug-delivery systems into rats to examine their effects.

Kohane said the “key” ingredient was saxitoxin, a known antibiotic, that produced nerve blocks lasting up to two days.

When saxitoxin was combined with the steroid dexamethasone, the nerve block extended for seven days, said Epstein-Barash.

Unlike conventional anesthetics, which often cause toxicity to surrounding tissues, impeding the development of slow-release anesthetic systems, the sustained release formulation containing saxitoxin resulted in very high local concentration—“the rat’s leg fell asleep”, said Kohane—but surrounding tissue did not sustain damage.

“The real importance is not just in getting very long nerve blocks, but getting long nerve blocks with no local toxicity and no systemic toxicity,” Kohane added.

While there is still a long way to go from testing in rats to clinical trials in humans, “it looks very promising”, said Epstein-Barash.

“Hopefully there will be a lot of applications for this when patients have pain from either operations or a chronic condition,” said Robert S. Langer, one of the authors and a professor of chemical engineering at MIT. “This could possibly lead to the first long acting nerve block, which is very exciting.”

—Staff writer Alissa M. D’Gama can be reached at adgama@fas.harvard.edu.

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