Scientists develop numbing drug, raising hopes for pain-free recovery

Scientists at Boston Children’s Hospital have developed an experimental drug delivery system that extended the effects of local anaesthesia to two to three weeks in rats, potentially opening a new avenue for longer-lasting pain relief after surgery.

The findings, published in Nature Biomedical Engineering, show that redesigned microscopic carriers called liposomes can release a powerful numbing agent much more slowly than conventional formulations.

The researchers said the approach could eventually help manage postoperative pain for longer periods and potentially reduce reliance on opioid painkillers. However, the treatment has not yet been established as safe or effective in humans.

The team loaded the liposomes with tetrodotoxin, a potent neurotoxin found in pufferfish and blue-ringed octopuses. The substance blocks sodium channels in nerve cells, preventing them from transmitting electrical signals and producing a numbing effect.

In experiments involving rats, the formulation sustained a nerve block for two to three weeks, compared with approximately four to eight hours for the commercial formulation used for comparison.

The researchers reported no detectable toxicity at the injection site or elsewhere in the animals under the conditions tested.

Liposomes are microscopic structures made from lipid molecules that can carry medication and release it gradually. Scientists have traditionally expected more fluid lipid membranes to release drugs faster because their molecules are less tightly packed.

However, research engineer Yuan Wang, working in the laboratory of Daniel Kohane at Boston Children’s Hospital, found that water-soluble drugs behaved differently.

The team discovered that these drugs escaped unusually slowly from more fluid liposomes. Further experiments revealed that the carriers contained multiple internal compartments, creating layers resembling an onion.

The researchers believe these additional barriers slow the drug’s release, allowing the body to clear it gradually while maintaining concentrations sufficient to block nerve signals.

Daniel Kohane, who leads the Laboratory for Biomaterials and Drug Delivery at Boston Children’s Hospital, said the approach could have applications in pain management around the time of surgery and potentially in chronic pain treatment.

The researchers also suggested that the liposomes could provide the slow release of a wider range of water-soluble molecules, potentially expanding the technology beyond local anaesthesia.

However, tetrodotoxin is highly poisonous, and its use presents significant safety challenges. The absence of detectable toxicity in rats does not establish that the formulation would be safe in people.

Further studies are needed to determine the appropriate dose, assess potential side effects and establish whether the prolonged anaesthetic effect can be reproduced in humans.

Although nerve blocks can last longer in people than in rats, the duration and safety of this particular formulation in patients remain unknown.

The findings offer a potential new direction for long-lasting pain relief, but the treatment remains experimental and is not yet available for routine clinical use.