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.