In this research work, a new biocompatible microemulsion containing castor oil has been formulated to increase the solubility of celecoxib, as a well-known anti-inflammatory drug. In this formulation castor oil has also anti-inflammatory properties. The proposed oil-in-water microemulsion composed of tween 80 as surfactant, isobutanol as co-surfactant, and castor oil as the oil phase. In the first step, the phase diagrams of the microemulsion systems with surfactant to co-surfactant mass ratios of 4:1 and 2:1 were prepared at ambient temperature. Then, using the obtained phase diagrams, the appropriate formulations were selected by combining different percentages of water, oil, surfactant and co-surfactant in the microemulsion region. Some of physic-chemical properties, such as electrical conductivity, density, refractive index, surface tension and particle size of the selected microemulsion formulations have been determined at 298 K. After that, the solubility of celecoxib in the selected formulations was determined and compared with other reported microemulsion formulations. Interesting results from this section indicated that the solubility of celecoxib significantly increased compared to pure water and the previous proposed microemulsion formulations. The results of this study can be used to provide suitable formulations based on the biocompatible microemulsions for celecoxib in pharmaceutical industry.
