Formation of drug/surfactant catanionic vesicles and their application in sustained drug release.

The aggregation behavior of the cationic drug/anionic surfactant vesicles formed by tetracaine hydrochloride (TH) and double-chain surfactant, sodium bis(2-ethylhexyl)sulfosuccinate (AOT), was investigated. By controlling the molar ratio of TH to AOT, a transition from catanionic vesicles to micelles was observed. The catanionic aggregates exhibited different charge properties, structures, interaction enthalpies and drug release behaviors depending on the composition. To characterize the cationic drug/anionic surfactant system, transmission electron microscopy (TEM), dynamic light scattering (DLS), isothermal titration calorimetry (ITC), conductivity, turbidity and zeta potential (ζ) measurements were performed. The drug release results indicate that the present drug-containing catanionic vesicles have promising applications in drug delivery systems. Furthermore, the percentage of drug distributed in the catanionic vesicles or micelles can be obtained by comparing the cumulative release of the corresponding aggregates with the pure drug solution.