Diclofenac Solubilization in Microemulsions Based on Mixed Nonionic Surfactants and R (+)-limonene

Diclofenac is a nonsteroidal anti-inflammatory drug that reduces inflammation and pain hormones in the body. Dispersing the drug in water is impossible and its solubility in oils is very limited. In this study, we solubilized sodium diclofenac in nanostructures of the constructed U-type water/sucrose laurate/ethoxylated mono-di-glyceride/oleic phase microemulsions. The mixing ratio (w/w) of sucrose laurate/ethoxylated mono-di-glyceride equals unity. The oleic phase was the pure R (+)-limonene or R (+)-limonene mixed with ethanol at a weight ratio equals unity. The solubilization capacity of the drug in these systems is many times higher than in either oil or water systems. The sodium diclofenac solubilized microemulsions are fully diluted with water without phase separation. The solubilization capacity decreases as the water content increases. The system free of alcohol solubilizes less amounts of drug over all the range of water contents compared to the system containing alcohol. Small angle x-ray scattering was used to evaluate the effect of solubilized sodium diclofenac on the microstructure and diffusion properties of the loaded microemulsions. From the periodicity and correlation length measured by small angle x-ray scattering, we learned that the drug affects the structure of loaded microemulsion droplets probably less spherical than the empty systems. The transition from water-in-oil to a bicontinuous phase occurs at the different water contents compared to the empty (i.e., without drug) microemulsions. The drug remains solubilized at the interface upon further dilution with water and is oriented with its hydrophilic part facing the water, and strongly affects the inversion to oil-in-water droplets.