Investigation of the particle size distribution of a model intravenous emulsion.

The size distribution of a model intravenous (iv) emulsion was investigated with special regard to the lower size classes. The special interest in the lower size classes is related to their possible responsibility for a number of side effects as well as their possible influence on pharmacokinetics of incorporated drugs. The particle size distribution of the unfractionated emulsion observed by photon correlation spectroscopy (PCS) showed no particles with diameters < 140 nm. In contrast, a three-dimensional analysis of transmission electron micrographs (TEM) resulted in a mean particle diameter of approximately 68 nm. 31P NMR experiments revealed that approximately 48 mol% of the emulsifier forms particles smaller than approximately 100 nm in diameter. The results from TEM observations and NMR spectroscopy suggest that the majority of particles by number have diameters < 100 nm. PCS measurements of fractionated samples of the emulsion, in combination with their chemical analysis, confirmed the predominance of particles with diameters < 100 nm. The relevance of PCS data analysis for the characterization of unfractionated iv emulsions, consisting of particles differing in structure and showing a broad size distribution by number, seems limited.