Menthol facilitates the skin analgesic effect of tetracaine gel

The aim of this study is to observe the effect of menthol on the percutaneous penetration and skin analgesic action of tetracaine gel (T-gel). Anesthetic gels containing 4% tetracaine in carbomer vehicle with and without menthol were prepared. The menthol penetration-enhanced gel conferred significantly higher diffusion of tetracaine across full-thickness mouse skin than non-penetration-enhanced gel, in a dose-dependent manner. The inter-cellular spaces of the stratum corneum in skin treated with menthol penetration-enhanced gel became extended as compared with those in non-penetration-enhanced gel. This may suggest that menthol's action was related to the changes of the epidermis ultra structures. An enlarged inter-cellular space, per se, would allow a better passage to tetracaine. To determine the efficacy of menthol penetration-enhanced tetracaine gel in the management of pain, a double-blind, placebo-controlled, randomized controlled trial (RCT) design was used. The mean verbal pain scores (VPS) were significantly lower in volunteers treated with penetration-enhanced tetracaine gel than those in volunteers receiving non-penetration-enhanced tetracaine gel or placebo. Menthol improved the analgesic efficacy of the tetracaine 4% gel in part through enhanced percutaneous permeation.