Characterisation of Drug Release from Cubosomes Using the Pressure Ultrafiltration Method

Cubosomes have been proposed as a controlled release, intravenous drug delivery system. The objective of this study was to characterise cubosomes as either a therapeutically useful, controlled release delivery system, or as a burst release carrier such as submicron emulsions. The pressure ultrafiltration method and equilibrium dialysis were used to elucidate the in vitro drug release mechanisms. On dilution of cubosomes, lipophilic compounds were released rapidly when studied by the pressure ultrafiltration method. This agrees with the behaviour predicted from simple diffusion from the bulk non-dispersed cubic phase. In contrast, equilibrium dialysis incorrectly indicated sustained drug release from cubosomes. This study illustrates that cubosomes should be classified as a burst release delivery system where drug is released by diffusion from the cubic phase matrix, and that pressure ultrafiltration may have benefits over dialysis methods for measurement of drug release from colloidal particle-based drug delivery systems.