The aim of this work was to prepare an erythromycin (EM) microemulsion (EM- microemulsion) for transdermal EM delivery using isotropic mixtures of oil and aqueous phases. The prepared EM-microemulsion is a white dispersion, with a suitable viscosity for transdermal delivery. In stability experiments, the EM-microemulsion showed no marked change in appearance for up to 3 weeks at 25 degrees C. In accelerated stability experiments at 37 and 60 degrees C, however, precipitated crystalline EM particles were observed in the EM-microemulsion. Diffusion of EM into the skin exhibited a first order release profile. Fluorescein (FL)-microemulsion penetrated to the dermis layer of skin. In conclusion, we confirmed that EM-microemulsion could serve as an excellent transdermal carrier of EM. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013