Transdermal anaesthesia with lidocaine nano-formulation pretreated with low-frequency ultrasound in rats model.

Rapid local transdermal anaesthetic is desirable in clinic. In this paper, lidocaine loaded poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL) nanoparticles were prepared, and a novel transdermal lidocaine formulation: lidocaine loaded PCL-PEG-PCL nanoparticles in F127 hydrogel (Nano-Lido Gel), was demonstrated. These lidocaine loaded PCL-PEG-PCL nanoparticles with mean particle size of ca. 200 nm had drug loading of about 40%. The efficiency of transdermal anaesthesia of four treatments: EMLA cream (E), Nano-Lido Gel (N), EMLA cream with brief focal ultrasound pretreatment (EU), and Nano-Lidocaine Gel with brief focal ultrasound pretreatment (NU), was evaluated by tail-flick latency test assay in rats. Results indicated that the topical anaesthesia onset time in NU was 5 times and 2.5 times shorter than that in E and EU. The efficiency of anaesthesia in NU, expressed as maximum possible effects (MPE) value, was significantly higher than that in other treatments. It provided a novel path to develop rapid transdermal anaesthesia by combination of ultrasound pretreatment and lidocaine nano-formulation based on polymeric nanoparticles.