Introduction to Colloidal Drug Carriers

CDC are defined only by their size (most scientists agree on sizes below 1 pm others set 0.5 pm as the upper limit). CDC are very heterogeneous in all other aspects (e.g., thermodynamic stability, chemical composition, and the physical state, including solid, liquid, or liquid-crystalline dispersions) [ 1 ]. The most prominent examples are nanoparticles, nanoemulsions, nanocapsules, liposomes, nanosuspensions, (mixed) micelles, microemulsions, and cubosomes. Some CDC have reached the commercial market. Probably the best known example is the microemulsion preconcentrate of cyclosporine (Sandimmun-Neoral), which minimized the high variability of pharmacokinetics of the Sandimmun formulation. In addition, intravenous injectable CDC have been on the commercial market for many years. Examples include nanoemulsions of etomidate (Etomidat-Lipuro) and diazepam (Diazepam-Lipuro) [2-4], mixed micelles (Valium-MM, Konakion), and liposomes (AmBisome) [5]. 

The pioneer in this field was Speiser, who developed nanopellets for peroral administration [7], These nanopellets were produced by dispersing melted lipids with high-speed mixers or with ultrasound. A relatively large amount of microparticles was present in these formulations, which might not be a serious problem for peroral administration, but they exclude an intravenous injection. Lipospheres, produced by high-shear mixing or ultrasound, were developed by Domb and represent similar systems [8-10], They also contain large amounts of microparticles. 

It was soon found that HPH is more effective for the production of submicronsized dispersions of solid lipids than is high-shear mixing or ultrasound [11-13], Dispersions obtained in this way are called SLN. Most SLN dispersions produced by HPH are characterized by an average particle size of around 100 to 200 nm and a low microparticle content. Alternative production procedures were also investigated, including the combination of organic solvents and HPH (HPH/solvent evaporation) [14], the dilution of microemulsions [15,16], and solvent injection [17], 

It has been claimed that SLN combine the advantages of other colloidal carriers and avoid their disadvantages [18], Proposed advantages include  

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