Formulation and evaluation of release and swelling mechanism of a water-in-oil emulsion using factorial design

Water-in-oil emulsions have a potential as a parenteral prolonged release s ystem for hydrophilic drugs. A consistent challenge when developing an emul sion drug delivery system is to obtain a proper release characteristic of t he entrapped drug. The aim of the present study was to study the release me chanism from water-in-oil emulsions. Secondly, to study the effects of drop let size, phase ratio and osmotic pressure on the release rate of glucose f rom water-in-oil emulsions in a factorial experimental design. The release mechanism of glucose was deduced from the release kinetics of two coentrapp ed marker molecules, glucose and inulin, with a molecule weight of 180 and 5000 g/mol, respectively. The results indicate that release of glucose was dominated by diffusion through the oily barrier as opposed to membrane rupt ure. Using statistical methodology, the release rate of glucose could be va ried 8 fold in a controled manner with osmotic pressure as the most importa nt parameter. The osmotic behaviour of the emulsions was further studied in a dynamic swelling study. These results show that the release of entrapped hydrophilic drug can be controlled within certain limits using pharmaceuti cal formulation principles. (C) 1999 Elsevier Science B.V. All rights reser ved.