Effect of nonionic surfactants on penetration of dissolved benzocaine through hairless mouse skin

The penetration of benzocaine from solutions containing polyoxyethylene onylphenols through hairless mouse skin was studied using an in vitro apparatus. Diffusion through STRATUM CORNEUM was the rate limiting step in benzocaine transport. Penetration flux in solutions containing a fixed benzocaine concentration was inversely related to surfactant concentration and polyoxyethylene chain length. In the case of solutions aturated with benzocaine, none of the surfactants had a significant effect on benzocaine flux. All experimental results could be reconciled by consideration of the concentration of free (not solubilized) benzocaine in solution. Bezocaine penetration was proportional to the free benzocaine concentration. Surface active agents are often included in topical formulations for a variety of purposes. However, possible ffects on percutaneous absorption should be considered. Of the various surfactant classes, the nonionic have the least tendency to interact with the skin barrier and alter membrane permeability (1-4). In studies designed to probe the influence of nonionic surfactants on percutaneous penetration of chemical agents, penetration sometimes increased. Other studies showed a reduction in penetration while in some cases, no change in penetration was evident. Vinson and Choman (5