Gastrointestinal lipophilic drug absorption systems

Microemulsions are transparent systems of two immiscible fluids, stabilized by an interfacial film of surfactant or a mixture of surfactants, frequently in combination with a cosurfactant. These systems could be classified as water-in-oil, bicontinuous, or oil-in-water type depending on their microstructure, which is influenced by their physicochemical properties and the extent of their ingredients. - SMEDDSs form transparent microemulsions with a droplet size of less than 50 nm. Oil is the most important excipient in SMEDDSs because it can facilitate self-emulsification and increase the fraction of lipophilic drug transported through the intestinal lymphatic system, thereby increasing absorption from the gastrointestinal tract. Long-chain and medium-chain... 

In absorption studies, the appUcation of colloidal systems, which show specific and unspecific interactions with mainly lipophilic substances is of main interest. An obvious application is the study of lipophilic and poorly absorbable drugs that are administered orally or transdermally. Such interactions with surface-active agents may either cause a diminution of the bioavailability by trapping the drug in the micelle or, on the other hand, lead to an improved solubility (prevention of the precipitation of the drug) and facilitated transfer of the solute across lipid membranes (e.g., the intestinal wall in the gastrointestinal tract) and therefore to an improved bioavailability. 

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