Percutaneous penetration characteristics of amethocaine through porcine and human skin

Abstract

Percutaneous amethocaine gels produce clinically effective local anaesthesia of intact skin. The present study establishes the percutaneous penetration characteristics of amethocaine from such gels through human stratum corneum, epidermis and whole skin barriers. Results are compared with neonate porcine stratum corneum, porcine whole skin and Silastic® as alternative model barrier membranes. Silastic® was shown to overestimate considerably the flux of amethocaine but neonate porcine skin proved to be a good model for the penetration of the drug through human skin. Differences in barrier membrane resistance to amethocaine penetration, and the effect on drug flux of varying the amethocaine concentration in the gel, were analysed separately by a one-way analysis of variance and the Newman-Keuls multiple range test. The main barrier to percutaneous penetration of amethocaine was the stratum corneum. The efficiency of the gel formulation in promoting the percutaneous penetration of amethocaine was reflected in the relatively high fluxes of the drug through both types of stratum corneum. The percutaneous penetration characteristics of amethocaine observed in this study, together with the pharmacological properties of the drug itself, explain the rapid onset and long duration of anaesthesia obtained clinically with the use of amethocaine percutaneous anaesthetic gel.