Prapaporn Boonme. Influences of microemulsion microstructure and surfactant type on the efficiency of skin permeation of hydrophobic and hydrophilic drugs . Doctoral Degree(Pharmaceutics). Mahidol University. : Mahidol University, 2006.
Influences of microemulsion microstructure and surfactant type on the efficiency of skin permeation of hydrophobic and hydrophilic drugs
Abstract:
Microemulsions of isopropyl palmitate (IPP)/water/Brij 97:1-butanol (2:1) and IPP/water/Aerosol OT (AOT):1-butanol (2:1) systems were characterized by several experimental techniques. The influences of microemulsion type and surfactant systems on the skin permeation of drugs with different hydrophilicity were evaluated. Three local anesthetic drugs, i.e. lidocaine, tetracaine and dibucaine and their hydrochloride salts were used as model hydrophobic and hydrophilic drugs, respectively. The results from observation of appearance, conductivity, viscosity, DSC, cryo-FESEM and NMR show that both IPP/water/Brij 97:1-butanol (2:1) and IPP/water/AOT:1-butanol (2:1) systems provided identical microemulsion regions in the pseudoternary phase diagrams and had similar transition points from water-in-oil (w/o) to oil-in-water (o/w) types at 30%-35% w/w water for the systems of 45% w/w surfactant mixtures. In addition, the characterization results indicate that FRET would be an alternative technique for characterization of the AOT-based microemulsions. Incorporation of 1% w/w model drug to the w/o and o/w microemulsions of 45% w/w surfactant mixtures and 15%/39% w/w internal/external pseudophase ratio did not alter the microemulsion type. From the skin permeation study through heat-separated human epidermis using modified Franz diffusion cells, the results exhibit that the nature of microemulsions was the crucial parameter for transdermal drug delivery. For all microemulsion systems, the o/w microemulsions of hydrophobic drugs provided the highest skin permeation enhancement. The skin permeation flux of the low molecular weight drug was greater than that of the high molecular weight drug. The AOT-based microemulsions provided higher skin permeation of the lidocaine group than the Brij 97-based microemulsions whereas permeation of the tetracaine group from the Brij 97-based microemulsions was higher. For the dibucaine group, skin permeation efficiency from the two microemulsion systems was comparable. The difference in the permeation efficiency of drugs from these two surfactant systems might be due to different enhancement effects of surfactants as well as interaction between drugs and surfactants