Long-lasting infiltration anaesthesia by lidocaine-loaded biodegradable nanoparticles in hydrogel in rats.

Background: Infiltration of a long-lasting anaesthetic is helpful during the post-operative period. The recently developed local drug delivery system, biodegradable nanoparticles in a thermo-sensitive hydrogel (nanogel system), may possibly provide an extended duration of drugs. Therefore, we evaluated whether prolonged infiltration anaesthesia could be achieved by loading lidocaine into this delivery system.
Methods: Thirty male rats were randomized into five groups of six rats each: saline; 2% hydrochloride lidocaine solution; lidocaine-loaded nanogel system and its compositing formulations, namely lido-nano gel; lido-nano; and lidogel. Durations of local anaesthesia with subcutaneously injected agents were measured by tail flick latency tests in a randomized, blind fashion.
Results: Lido-nano gel produced effective anaesthesia for 360+/-113 min, compared with 150+/-33 min by lidogel, 180+/-37 min by lido-nano, and 110+/-45 min by lidocaine solution (P<0.001, means+/-SD), and elicited complete sensory blockade for 300+/-114 min, compared with 75+/-37 min by lidogel, 105+/-53 min by lido-nano, and 60+/-33 min by lidocaine solution (P<0.001, means+/-SD) without severe skin/systemic toxicity.
Conclusion: Lidocaine-loaded biodegradable nanoparticles in hydrogel produced prolonged infiltration anaesthesia in rats without severe toxicity, indicating a possible way to develop long-lasting local anaesthetics.