Injectable slow acting anaesthetic can banish prolonged pain

April 16th, 2009 - 3:42 pm ICT by IANS  

New York, April 16 (IANS) Paediatric researchers have developed a slow-acting anaesthetic that could banish prolonged pain during and after surgery.
Researchers used specially designed fat-based particles called liposomes to package saxitoxin, a potent anaesthetic. They then produced a long-lasting local anaesthesia in rats minus apparent toxicity to nerve or muscle cells.

“The idea was to have a single injection that could produce a nerve block lasting days, weeks, maybe even months,” explained Daniel Kohane, of critical care medicine in the Department of Anaesthesiology at Boston Children’s Hospital, and study co-author.

“It would be useful for conditions like chronic pain where, rather than use narcotics, which are systemic and pose a risk of addiction, you could just put that piece of the body to sleep, so to speak.”

Previous attempts to develop slow-release anaesthetics have been unsuccessful due to the tendency for conventional anaesthetics to cause toxicity to the surrounding tissue.

Indeed, drug packaging materials have themselves been shown to cause tissue damage. Now, Kohane and colleagues reported that if saxitoxin is packaged within liposomes, it is able to block nerve transmission of pain without causing significant nerve or muscle damage.

In lab experiments, the researchers evaluated various formulations - different types of liposomes containing saxitoxin with or without dexamethasone, a potent steroid known to augment the action of encapsulated anaesthetics.

The best liposomes produced nerve blocks lasting two days if they contained saxitoxin alone and seven days if combined with dexamethasone. Cell culture experiments and tissue analysis confirmed that the formulations were not toxic to muscle or nerve cells, said a Boston release.

“If these long-acting, low-toxicity formulations of local anesthetics are shown to be effective in humans, they could have a major impact on the treatment of acute and chronic pain,” said Alison Cole of the National Institute of General Medical Sciences.

The study was published online by the Proceedings of the National Academy of Sciences.

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