OBJECTIVETo prepare lidocaine nanoemulsion and investigate its transdermal delivery ability in vitro.

METHODSThe optimal Km (surfactant/cosurfactant) value and the component proportion were determined by pseudoternary phase diagrams combined with Origin software analysis. The diameter and distribution range were detected by Zeta particle size analysis instrument, and the morphology of the nanoemulsion was observed by electron microscope. The permeation flux of lidocaine was determined in vitro using the modified Franz diffusion cell combined with HPLC, and the cumulative transdermal absorption amount and the apparent skin transdermal velocity were compared among nanoemulsion, gel and tincture containing 5% lidocaine. The permeation mode of lidocaine nanoemulsion was analyzed.

RESULTSThe average drop size of lidocaine nanoemulsion was 29.8-/+14.4 nm, and 98% of the drop sizes ranged from 15.1 to 45.5 nm and 2% from 77.9 to 261.3 nm. The nanoemulsion drop showed a spherical morphology in a polydisperse system. The Kp value of the nanoemulsion (3.07-/+0.74 cm/h) was significantly higher than that of gel (1.27-/+0.35 cm/h) and tincture (0.97-/+0.18 cm/h), and the permeation rate of the nanoemulsion was 69.82-/+7.48 microg x cm(-2) x h(-1), which fitted the the Zero-order release dynamic procedure.

CONCLUSIONSThe component proportion of lidocaine nanoemulsion can be conveniently obtained through pseudoternary phase diagrams and Origin software analysis, and the drop size, distribution, morphology and system type can be determined by Malvern Zetasizer combined with electron microscopy. The results also indicate that the nanoemulsion system with high permeation rate may provide a new promising means for local anesthesia.