The effect of internal structure of selected water-Tween 40-Imwitor 308-IPM microemulsions on ketoprofene release.

Microemulsions are a promising vehicle for administrating drugs. In order to lay the basis for predicting drug release under in vivo conditions, where the microemulsion composition is continuously varying, we have studied the release of ketoprofene as a model drug, from microemulsions on a dilution line containing, initially, 20 wt.% of isopropyl miristate (IPM) and 80 wt.% of the surfactant (Tween 40/co-surfactant (Imwitor 308, 1:1 wt.% mixture. Mixture compositions corresponding to the different types and structure of microemulsion were identified by measuring density, surface tension, electric conductivity, pH and differential scanning calorimetry. Ketoprofene release was then measured for each type and structure. The main factor influencing ketoprofene release was shown to be the strength of the interactions between microemulsion components. Strong interactions prevented rapid ketoprofene release in the water-in oil region, although the release was not dependent on the degree of percolation. Release kinetics in all cases follow zero order kinetics, indicating that the release rate is dependent on the diffusion of ketoprofene inside the microemulsion carrier. Combining different methods to obtain the physical and structural properties of microemulsions can be thus used to predict the release of ketoprofen from a microemulsion.