The phospholipids have received much attention as a useful material in designing pharmaceutical preparations partly because of its biocompatibility. Lipid vehicle consisting of phospholipids is one of the promising carrier systems for various drugs. So far, some drug delivery systems of lipid vehicles have been developed and commercially available. This paper will report that the surface modification of lipid vehicles with suitable polymers leads to producing the more functional drug carriers. The studies reviewed in this paper may contribute to development of the oral delivery systems of peptide drugs, long circulating drug carriers and so on.

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Liposomes represent various properties of electric charge, thermo-sensitivity, pH-sensitivity and fusion by regulation of lipid composition and size. Properties of membrane control biological behavior, drug-trapping efficiency and drug-releasing property as DDS carrier. Liposomal biodistribution depends on opsonization of plasma protein which can be controlled by membrane fluidity and PEG-coating. Drug-trapping efficiency and drug-releasing property also depend on fluidity of membrane. This character is useful for thermo-sensitive liposomes. Liposomes are also used as vector of anti-sensene DNA and plasmid DNA, because these properties of liposomal membrane can introduce genes into cells. Cationic liposomes enhance the ability of DNA-packing and attachment to cells, this property increase the transfection. Functional pH-sensitive liposomes and fusogenic liposomes can improve the transfection of pDNA. Optimal liposomes with progress of biological membrane will be developed.

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Lipid emulsions employed in drug delivery systems are stabilized by the natural emulsifying agent lecithin, phospholipids obtained from egg or soybean. These are o/w emulsions formulated by soybean oils or medium chain triglycerides as oil phases and similar to commercially available fat emulsions employed in parenteral nutrition. Lipid emulsions are useful microparticle drug carriers in various therapeutic applications owing to their ability to incorporate lipid-soluble drugs or prodrugs modified from water-soluble drugs in oil phase of dispersing systems. Recent topics containing gene delivery in the study of lipid emulsions are reviewed.

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