The Influence of Microstructure on Celecoxib Release from a Pharmaceutically Applicable System: Mygliol 812®/Labrasol®/Plurol Oleique®/Water Mixtures

Structural transformations were investigated in unloaded and celecoxib-loaded microemulsions on a dilution line containing, initially, 12 wt. % of Mygliol 812R and 88 wt. % of the surfactant (LabrasolR)/co-surfactant (Plurol OleiqueR), 4:1 wt. % mixture. Electrical conductivity, viscosity, surface tension and density measurements revealed that two structural transitions take place along the dilution line studied. At ∼27 wt. % of water the oil-continuous (w/o) system converted to a bicontinuous microemulsion and a transition to a water-continuous (o/w) microemulsion followed at ∼45 wt. % of water. After incorporation of celecoxib at 1 wt. % concentration the microemulsion remained stable and no change in its microstructure was observed. Celecoxib release was then measured for each type of microemulsion. It was shown to be influenced by the microstructure and solubilization capacity of the system, and can, to a certain extent, be predicted. Stability testing of celecoxib-loaded microemulsions revealed that they are stable over 90 days storage at 40 °C.