Parenteral emulsions droplet size distributions

Emulsifying agents are used both to promote emulsification at the time of manufacture and to control stability during a shelf life that can very from days for extemporaneously prepared emulsions to months or years for commercial preparations. In practice, combinations of emulsifiers rather than single agents are used. The emulsifier also influences the in vivo fate of lipid parenteral emulsions by its influence on the surface properties of the droplets and on the droplet size distributions. For convenience, most pharmacy texts classify emulsifiers into three groups i) surface active agents ii) natural (macromolecular) polymers and hi) finely divided solids. 

For parenteral emulsions, the formulation scientist must be particularly aware of changes in particle size distribution of the oil phase. Droplet coalescence results in increased droplet size. As a general rule, average droplet size should be less than 1 pm. Droplet sizes of more than 6 pm can cause blockage of capillaries (capillary emboli). 

Phospholipid-stabilized intravenous emulsions have been widely used for parenteral nutrition and have also been introduced as drug carrier systems, especially for lipophilic compounds. The aim of the authors in the next papers we review here (50,51) was to consider in detail various methods, e.g.. PCS. nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and small-angle x-ray diffraction studies (SAXS), to determine parameters related to the internal structure of the particles in a model intravenous emulsion stabilired by phospholipids. An emulsion with an extremely high fat load and a da.ssical emulsifier was chosen, PCS measurements were used to derive a particle size distribution and this was then used to calculate the total ot droplet surface area. The result indicated that there should be an excess of surfactants of 1.50%, Such an excess was not confirmed by either NMR or SAXS measurements and the dis-... 

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