Long-acting non-toxic local anaesthetic
Researchers have developed a single injection that is capable of producing long-term local anaesthesia in rats. By packaging the anaesthetic in fat-based particles called liposomes, it was released gradually, rather than all at once.
Local anaesthetics are often used during and after surgery to manage pain. They work by blocking the nerve signals to the area where pain is being experienced, stopping the pain signals from reaching the brain.
Previous attempts at developing long-lasting local anaesthetic formulations have stumbled; they haven't lasted long enough, or have been toxic to the body and the surrounding tissues. The concept of packaging the anaesthetic has been investigated, but past packaging materials have caused tissue damage too. Liposomes show promise as they are able to encase the anaesthetics without causing damage or toxicity.
The team tested liposomes containing the anaesthetic saxitoxin in rats. After a single injection, the anaesthetics blocked the nerve signals for two days. They also tested saxitoxin in combination with a steroid called dexamethasone, which is known to enhance the action of anaesthetics. The rats which received this combination showed nerve blocks that lasted a week. Tissue analysis after administration did not show toxicity in either muscle or nerve cells.
This could be significant not only for pain following surgery, but could also be used to treat chronic pain, without the problem of addiction associated with narcotics. The slow-release ability of liposomes could also have implications for a variety of other medicines.
The team is currently working to optimise the formula to make it last longer without becoming toxic, with a view to starting clinical trials.