Fully dilutable microemulsions embedded with phospholipids and stabilized by short-chain organic acids and polyols

Evidence on the role of phosphatidylcholine (PC) as a membrane permeability enhancer was the driving force in forming new liquid nanosized (modified microemulsions) oral delivery system containing PC molecules. In this study we have demonstrated the feasibility of constructing phase diagrams with a large isotropic regions capable of being fully diluted with water. The microemulsions were stabilized with mixtures composed of PC and nonionic surfactant (polyoxyethylene-40 hydrogenated castor oil, HECO40) and short-chain organic acid as cosurfactant/cosolvent. When propionic acid served as the cosurfactant/cosolvent, the isotropic region was at its maximum (ca. 72% of the total phase diagram area). The presence of a blend of PC and HECO40 seems to have synergistic effects, forming an isotropic region comprising 72% of the area of the phase diagram, in comparison to 20 and 50% in systems stabilized by PC and HECO40, alone, respectively. The role of the PC molecules in the formation of those microemulsions is demonstrated by comparing three soy lecithins. Lecithin with a high PC content forms larger isotropic regions with more "free dilution" lines. Several nonionic surfactants have been investigated, yet only HECO40 seems to have a packing parameter suitable for the formation of large isotropic U-type systems. (c) 2006 Elsevier Inc. All rights reserved.