Abstract

Microemulsions are widely used as potential drug delivery systems, especially through the dermal route as a means to avoid systemic side effects. Also, it is well known that the formation and characteristics of MEs depend on their composition. This study aimed to investigate the influence of various types and ratios of components which could dissolve diclofenac sodium on ME formation in term of size of ME regions through the construction of sixteen pseudoternary phase diagrams using the titration method. The data obtained were used to prepare oil-in-water and water-in-oil diclofenac sodium MEs. Two o/w and two w/o blank microemulsions were selected from the system providing the largest ME region and these were subsequently incorporated with 1 % w/w diclofenac sodium. Afterward, their physicochemical and drug release properties were assessed. The largest ME region was found in the system consisting of 2:1 Cremophor RH40:Span 80, ethylhexyl palmitate and 2:1 water:isopropanol. Characteristics of diclofenac sodium MEs were similar to those of their blank counterparts, with the exception of the drug-contained MEs having higher conductivity. Our findings indicated that compatibility of oil and surfactant structures was the crucial parameter for ME formation. Furthermore, the present research not only expanded the phase behavior studies of MEs using different blends of Cremophor RH 40 and Span 80 as surfactant and cosurfactant mixtures, but also reported the application of ethylhexyl palmitate in ME formulations. Incorporation of diclofenac sodium into four studied MEs did not affect ME type. Location of the drug, drug mobility and interfacial film rigidity in MEs were found to influence the release characteristics of the loaded drug.