Formulation and Evaluation of Stable Ascorbic Acid Multiple Emulsion

Objective: The Primary objective of the present investigation was to stabilize ascorbic acid by blocking its irreversible conversion to biologically inactive form. Further aim of the project was to disperse stabilized ascorbic acid in internal aqueous phase of multiple emulsions and deliver it in a suitable base for topical application and enhanced transdermal permeation. Materials and Methods: The o/w/o emulsions were formulated by a two-step emulsification procedure, with different types and ratios of surfactant and oil using sodium oxalate as a stabilizer. Physical and chemical stability of the optimized formulation was evaluated at 8°C, 25oC, 40oC and 40°C /75% relative humidity. Physical stability of the formulation was determined by organoleptic characteristics, globule size, viscosity, pH and conductivity. Ascorbic acid release profile was measured with Franz diffusion cell using sigma membrane Results: There was no change in color or liquefaction was observed in primary or multiple emulsion stored at 8°C, 25oC, 40°C and 40°C/75% relative humidity for a period of 6 months. Physical stability studies revealed change in globule size, phase separation and increase in pH for all primary and multiple emulsions kept at 40°C and 40°C/75% relative humidity. But there was only marginal change in pH and conductivity, globule size, and rheological parameters for multiple emulsions stored at 25C. In vitro release study showed that multiple emulsions followed a zero order release rate with an average flux value of 0.125 μg/cm2 /min. Conclusion: Based on the data, it was proved that multiple emulsion using sodium oxalate as a stabilizer remarkably improved the stability of ascorbic acid in aqueous solutions. The data given in this research led us to conclude that stabilized multiple w/o/w emulsion could be employed as a potential prolonged release vehicle for topical application of ascorbic acid.