Microemulsions as Antidiabetic Drug Delivery Systems

Glibenclamide is practically insoluble in water and its gastrointestinal absorption is limited by its dissolution rate. Therefore, to enhance the drug dissolution and its hypoglycemic effects, the drug was formulated in different microemulsion systems and in vitro/in vivo evaluated. Microemulsion systems were prepared by Water titration method in which surfactants and cosurfactants (S/CoS) were mixed at different weight ratios of 1:1, 2:1 and 3:1. They were subjected to transmission electron microscopical examination, pH determination and viscosity tests. The solubility of Glibenclamide in different microemulsion systems was determined. Forms 8, 9, 10, 11, 14 and 18 were found to have high Glibenclamide solubility using different oils. Form 11 and 9 showed the highest Glibenclamide release rates of 59.72% and 52.35%, respectively after 6 hours. In-vivo studies were tested using diabetic rats by application of form 11 with n-butanol as cosurfactant transdermally and form 8 with propylene glycol cosurfactant orally and transdermally. The results were compared to the drug suspension as a positive control. It was shown that microemulsion systems gave an effective tool of increasing drug dissolution probably due to enhanced wettability and reduced drug particle size, which in turn led to enhance its hypoglycemic effects. INTRODUCTION: Microemulsions, as drug delivery systems are becoming more and more important due to controlled release of drugs, improved bioavailability and stimulated rate and extent of absorption of lipophilic drugs . They are optically transparent, low viscous, thermodynamically stable dispersions of oil and water stabilized by surfactant, usually in combination with a cosurfactant. Microemulsions can be classified into three main types according to the ratios of the dispersed phase in relation to the dispersion medium to oil-in-water, water-in-oil and bicontinuous microemulsions . Transdermal drug delivery systems (TDDS) provide a means to sustain drug release as well as reduce the intensity of action and thus reduce the side effects associated with its oral therapy . It also ensures that the drug is not completely metabolized and delivered according to the desired pharmacokinetics and pharmacodynamics parameters . In-vitro dissolution rate is the rate limiting step in drug absorption and so as to increase concentration of the drug at the absorption sites, increasing the solubility of the drug is necessary. This was performed through microemulsion delivery system which is found to be preferable than conventional vehicles such as hydrogels, and emulsions or nonconventional systems such as liposomes 8, . Moreover, the oral bioavailability of poor water soluble drugs can be enhanced through microemulsion technology.