A method for the early evaluation of the effects of storage and additives on the stability of parenteral fat emulsions

Compositional heterogeneity in parenteral lipid emulsions after sedimentation field flow fractionation

This study examines the size and compositional heterogeneity of particles in a commercial lipid emulsion (Intralipid) before and after equilibration with penclomedine, a highly lipophilic cytotoxic agent. Emulsions were fractionated by sedimentation field-flow fractionation (sedFFF), and particle sizes of the monodisperse fractions were determined by photon correlation spectroscopy. The triglyceride (TG), phosphatidylcholine (PC), and penclomedine (in drug loaded emulsions) contents in each fraction were determined by HPLC. The aqueous-entrapped volume within Intralipid was determined to be approximately 10% by size-exclusion chromatography using [3H]mannitol. Thirteen sedFFF fractions collected from the drug free emulsions yielded particles ranging in size from 154 to 423 nm. Total channel recoveries were 89% and 95% for TG and PC, respectively. Apparent particle densities varied significantly with size, suggesting heterogeneity in composition as confirmed by PC/TG mass ratios which varied dramatically. Computer fits of the distribution profiles suggested populations of phospholipid vesicles and oil droplets containing excess phospholipid in addition to classical emulsion droplets. Drug loading induced a significant shift of the predominant triglyceride containing population to a larger particle size. The penclomedine distribution profile closely mimicked that of the TG rather than the PC fraction. These studies suggest the need to consider not only size distribution but also compositional distribution in characterizing parenteral emulsions.

Isolation and measurement of colloids in human plasma by membrane-selective flow field-flow fractionation: lipoproteins and pharmaceutical colloids

Using a modified flow field-flow fractionation (flow FFF) technique termed membrane-selective flow FFF, a capability is developed to isolate various colloidal constituents that are naturally present in or may be introduced into blood plasma. Once isolated, the colloids may be subject to quantitative measurement to provide relative amounts of the different constituents and the size distribution curve of each. The potential of the technique has been demonstrated by isolating and measuring (a) the lipoprotein fractions found in human blood plasma, (b) liposyn II pharmaceutical emulsion added at 2 mg/mL of plasma, and (c) amphotericin B colloidal dispersion (a drug delivery agent) added to plasma at 0.5 mg/mL.

The effect of lysine, a water-structure breaker, on the stability of phospholipid-stabilized emulsions

Phospholipid-stabilized emulsion properties were studied in the presence of lysine, a water-structure breaker, using two unrelated procedures, photon correlation spectroscopy and a light obscuration instrument. Commercial Intralipid was used as a control. Lysine 0.125, 0.25 and 0.5 M induced changes in the size distribution of a non-heated model emulsion system, irrespective of any changes produced by environmental pH. Some of the laboratory-prepared emulsions containing lysine were more stable than the corresponding commercial heat-sterilized product Intralipid, once heated. The results suggest that lysine is producing an effect on the nascent oil-water interface that controls the physical stability of the system. Once the heat-induced interfacial rearrangement of the individual phospholipid molecules occurs, the influence of lysine becomes diminished.

Simulation of fractograms of fat emulsions in power-programmed sedimentation field-flow fractionation (SdFFF)

A quasi-empirical approach to the simulation of fractograms was examined to verify that the elution behavior of emulsions in power-based field programmed sedimentation field-flow fractionation (SdFFF) is consistent and predictable. The approach was applied to Intralipid, a commercial soybean emulsion and to an investigational medium chain triglyceride emulsion. The simulations predicted the fractograms that were obtained under various conditions of field strength, field decay and velocity of the suspending fluid, using distribution parameters obtained from one preliminary measurement of size distribution profile. Predicted fractograms were compared to experimental ones, under various fractionating powers. Good agreement was observed in most cases, in which interference of the secondary relaxation effects was not effective. The agreement confirmed the applicability of the approach to emulsions and that the simulations can be used instead of actual experiments for the optimization of their characterization by power-programmed SdFFF.

Selective elution and purification of living Trichomonas vaginalis using gravitational field-flow fractionation

Gravitational field-flow fractionation is one of the simplest separation methods for biological materials. Its potential in parasitology is demonstrated for Trichomonas vaginalis, a parasite responsible for one of the most widespread sexually transmitted diseases. It was observed that this unicellular parasite can be purified in a culture medium with a recovery of 85% for the living trophozoites. The parasite retention characteristics were different when motile living and non-motile dead cells were eluted, motile cells being less retained than the non-motile cells.

Structural studies of commercial fat emulsions used in parenteral nutrition

In this paper, we demonstrate that by employing a combination of sedimentation field-flow fractionation (sedFFF) and other characterization techniques, such as photon correlation spectroscopy (PCS) and freeze-fracture electron microscopy (EM), it is possible to show that commercial fat emulsions of similar overall chemical compositions not only may exhibit different size distributions but may have different densities as well. A closer look at the density difference between droplet and suspension medium, on the one hand, and the droplet size, on the other, demonstrates that fat emulsions may have structures other than the traditional oil droplet surrounded by a monolayer of surfactant. From our determined and simulated density differences, we propose that these emulsion droplets may have a multilayered surfactant arrangement as well as an inclusion of water vesicles in the oil phase of the emulsion. Freeze-fracture EM observations provide evidence to confirm the existence of such complex structures. These findings are supported by recent EM work from other laboratories, as well as through chemical verification of elevated water contents in the oil droplets of these emulsions.

Use of the Walden Product to evaluate the effect of amino acids on water structure

The Walden Product, the product of viscosity (eta 0) and conductivity at infinite dilution of a solution (lambda 0), provides a measurement of the water-structuring activity of the solute. Measuring the effect of concentration on viscosity of solutions of amino acids, together with the conductivity of solutions of sodium chloride containing increasing concentrations of the amino acids, enabled Walden Products to be determined. The classical form of the Walden Product (lambda 0 eta 0) was used, together with a modified form, lambda 0 eta c, in which eta c was the slope of the concentration/viscosity curve. Most amino acids demonstrated modest water-structure-breaking activity but L-lysine, L-glutamic acid and L-aspartic acid, and their respective salts, all showed relatively higher activity. Dextrose behaved as a classical water-structure maker and, when added progressively, reversed the breaking activity of L-lysine. It is speculated that effects seen in bulk water may also occur at emulsion droplet surfaces, thereby inducing structural changes associated with the occasional rapid instability experienced when making admixtures of phospholipid-stabilized emulsions and additives such as amino acids and dextrose.

Characterization of submicron MCT o/w emulsions using sedimentation field-flow fractionation (FFF) with power field programming

Sedimentation field-flow fractionation (SdFFF) operated with power-based field programming, was shown to be effective in the characterization of submicron investigational pharmaceutical emulsions. Field programming, in which the decrease of field strength with time gradually decreases the retention of sample components, extends the capabilities of sedimentation field flow fractionation in handling polydisperse and multicomponent samples. The emulsions were made of medium chain triglycerides (MCT) oil in water emulsified by phospholipids. They were analysed by different rates of field decay and different flow rates. Identical size distribution profiles were obtained under all circumstances, using the appropriate stop-flow times. Fractions were collected from the SdFFF eluting bands, and diameters were analysed by photon correlation spectroscopy, showing good agreement with values given by the FFF instrument at high flow rates and low rates of field decay. Accurate and highly reproducible size distribution profiles were obtained under various conditions. The detector response was shown to consist mostly of light scattering and was linear with concentration.