Microemulsion: a novel transdermal delivery system to facilitate skin penetration of indomethacin

In this study, we aimed to develop thermodynamically stable microemulsion formulations of indomethacin with lower surfactant and cosurfactant contents, to improve drug permeability. Formulations were based on the oil/water microemulsion region of pseudo-ternary phase diagrams. The characteristic parameters (viscosity, diameter, and polydispersity) of the microemulsion formulations were then determined. In vitro permeation studies were performed using Franz diffusion cells. Permeation through mouse skin and skin retention of indomethacin microemulsions and ointment were tested. The cumulative amount of permeated indomethacin and its skin retention were significantly higher in microemulsion formulations compared with ointment. Drug flux and skin retention improved with decreasing droplet diameter of the microemulsions. On the basis of these results, we suggest some possible mechanisms for the enhanced transdermal permeation of drugs in microemulsions, including high drug-loading capacity, permeation enhancement by surfactants and cosurfactants, and smaller droplet diameter. In conclusion, microemulsions represent a novel transdermal delivery vehicle for increasing the solubility and permeability of indomethacin.