This thesis reports on the formulation, characterisation and in-vitro release characteristics of oil-in-water microemulsions containing egg or soya lecithin, ethanol, isopropyl myristate and water. The use of lecithin as a surfactant in the formulation of pharmaceutical microemulsions has been discussed. The various techniques used for particle size determination and the application of microemulsions in drug delivery have been reviewed. Oil-in-water microemulsion regions were detected for systems containing egg or soya lecithin/isopropyl myristate/ethanol/water with continuous phases of 80%, 70% or 60% w/w aqueous ethanol. No microemulsion region could be detected for systems containing 50% w/w ethanol solution. The effect of ethanol content on the size of the microemulsion region has been discussed. Static and dynamic light scattering measurements have been carried out on microemulsions prepared with egg or soya lecithin. The droplet radius has been determined by analysis of the static light scattering data using the Percus- Yevick hard sphere model. There was a decrease in droplet radius with an increase in lecithin content within the microemulsion region. An increase in droplet radius with an increase in oil content and also with a decrease in ethanol content of the aqueous phase has been noted. No significant difference in results obtained for microemulsions prepared with egg or soya lecithin has been detected. A correction for hard sphere interactions was applied to the dynamic light scattering data. The variation of droplet size with changes in the formulation determined by analysis of the results from dynamic light scattering was similar to that from static light scattering. However, there was poor correlation between droplet radii obtained from these two techniques for identical formulations with the radii obtained from dynamic light scattering being generally lower. The effect of various formulation parameters, such as droplet size, oil, lecithin or ethanol content on the release of two model drugs (methylene 'violet (Bernthsen) and methylene blue) from microemulsions prepared with soya lecithin has been examined. In-vitro release has been studied by examining diffusion of the model drugs across a hydrophilic cellulose membrane separating the microemulsions from a receptor solution of aqueous ethanol. The results have been related to the partition coefficients of the dyes between isopropyl myristate and aqueous ethanol and the release of the dyes from aqueous ethanol solutions. An increase in the rate of release of both dyes from the microemulsions of soya lecithin/ isopropyl myristate/ethanol/water with a decrease in lecithin content has been noted. An increase in oil content and hence droplet size has been found to cause an increase in the rate of release of methylene violet (Bernthsen). The release rate of methylene blue increased with increase of oil content up to 20% oil but decreased with further increase of oil content due to the instability of these microemulsions under the experimental conditions. The release rate of both dyes was found to decrease as the lecithin content of the micro emulsions increased. Release of methylene violet (Bernthsen) decreased as the ethanol content increased, however the trend was reversed for the release of methylene blue. Viscosity studies showed Newtonian flow behaviour for all the micro emulsion formulations used for drug release studies. An increase in viscosity with an increase in oil or lecithin content or a decrease in ethanol content was noted.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:588606 |
| Date | January 1994 |
| Creators | Saint Ruth, Helen Margaret |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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