Development of a microemulsion-based formulation to improve the availability of poorly water-soluble drug.

The objective of our investigation was to design a thermo-dynamically stable microemulsion formulation of the model drug piroxicam with minimum surfactant concentration in order to improve its solubility. The solubility of piroxicam in different oils was examined. Effects of the co-surfactant:surfactant ratio and water content on microemulsion formulation were evaluated. Phase studies were performed for systems composed of oleic acid as the oil phase, Tween-80 as surfactant, and propylene glycol as co-surfactant at a constant percentage of water to elucidate the effect of microemulsion components on the area of microemulsion formulation. The viscosity and conductivity of certain microemulsion formulations were examined as a function of water dilution. The results showed that oleic acid, Tween-80, and propylene glycol resulted in the highest solubilization of piroxicam. The amount of water that was successfully incorporated into a microemulsion system was directly proportional to the co-surfactant:surfactant ratio and inversely proportional to the percentage amount of the oil phase present in the system. Microemulsion systems displayed changes in their viscosity and conductivity upon water dilution. The pre-microemulsion systems could be used as solvents to provide enhanced solubilizing capacity and stabilization for the solubilized drug. These systems could be loaded with the drug and stored in their original form in order to produce a microemulsion containing the drug in situ upon aqueous dilution. The incorporation of piroxicam in microemulsion formulations led to enhancement of the piroxicam release profile by allowing constant and regular in vitro release as well as reducing piroxicam's particle size to that suited to a microemulsion. Thus, the usage of a microemulsion technique led to improvement in piroxicam availability, suggesting the potential for technique's use as a topical vehicle for piroxicam delivery.