Lipid Emulsions as a Drug Carrier

Abstract

Conventional lipid emulsions (LM), with a mean diameter of 0.2-0.3μm and consisting of soybean oil and lecithin, are used for parenteral carriers for site-specific drug delivery as well as for parenteral nutrition. Plasma lipoproteins are well known as endogenous colloidal lipid particles which have physiological roles to deliver many lipids to specific sites in the body and as a potential carrier of drugs. If a lipophilic drug joins with plasma lipoproteins, the amount of the drug entering tissues may vary widely because each lipoprotein has different metabolic fate. One might also expect that lipid emulsions with different size and/or compositions may show different characteristics of drug carriers. For example, a small lipid emulsion of particles, Lipid Nano-Sphere (LNS^®), with a mean diameter of 25-50nm, are characterized by lower uptake by the liver, prolonged plasma half-lives of drugs, and good distribution into sites of inflammation, tumor, etc. as compared with LM. The difference between them is explained by the affinities to apolipoprotein C-II and E. LM has high affinity to these apolipoproteins and rapidly enters into the liver like chylomicrons. In the both emulsions, they are in dynamic pathways of lipoprotein metabolism in the circulation. Several types of lipid emulsion with different properties as drug carrier are under investigations.