Water/oil type microemulsion systems containing lidocaine hydrochloride: in vitro and in vivo evaluation

Abstract

The purpose of this study was to develop a water/oil microemulsion containing lidocaine hydrochloride (4%) and to compare its local anaesthetic efficacy with commercial products. A pseudoternary diagram (K_m:1/1 or 1/2) was constructed using lecithin/ethanol/oil/water. The droplet size, viscosity and release of the microemulsions were evaluated. Tail flick tests were conducted for in vivo effectiveness; the initiation time of effect, maximum effect, time to reach maximum effect, and relative efficacy were evaluated. The drug caused a significant increase in droplet size. The use of olive oil resulted in a decrease in the solubilisation parameter, as well as a reduction in the release. The droplet size and viscosity of the microemulsion composed of Miglyol/lecithin/ethanol/water/drug (K_m:1/2) was lower than other microemulsions (8.38 nm, 6.9 mPa), and its release rate (1.61 mg/h) was higher. This system had a faster and more efficient anaesthetic effect than the other microemulsions and commercial products. Results indicate that a water/oil type microemulsion (Miglyol/lecithin/ethanol/water) has promising potential to increase the local anaesthetic effect.

• Local anaesthetic activity
• miglyol 818
• olive oil
• tail flick test

Acknowledgements

The authors would like to thank Abdi Ibrahim, Istanbul, Turkey for kindly providing the sample of lidocaine hydrochloride. This study, which is the master thesis of A. Dogrul, was presented as two posters at the 7^th World Meeting on Pharmaceutics, Biopharmaceutics and Pharmaceutical Technology, 2010, Malta and 14th World Congress on Pain (IASP), August 27–31, 2012, Milan, Italy.