AN INVESTIGATION INTO THE PHYSICOCHEMICAL PROPERTIES OF SELF-EMULSIFYING SYSTEMS USING LOW-FREQUENCY DIELECTRIC-SPECTROSCOPY, SURFACE-TENSION MEASUREMENTS AND PARTICLE-SIZE ANALYSIS

The structure and behaviour of self-emulsifying drug delivery systems (SEDDS) containing Labrafil M2125 CS and Tween 80 have been examined a nd the effects of changing the formulation via the addition of a non-p olar model drug (L-365,260) investigated. Low frequency dielectric spe ctroscopy (LFDS) was used to examine the individual components in orde r to investigate the effects of drug inclusion. The presence of the dr ug resulted in a decrease in the dielectric response of the Labrafil M 2125 CS, Tween 80 and the oil-surfactant vehicles. The surface tension of the emulsions decreased on addition of the drug, while particle si ze analysis showed that the emulsions containing no drug and 2% w/v dr ug had a bimodal distribution and the emulsions containing 6% w/v drug were unimodal. It was found that the bimodal distribution changed ove r a period of 14 h, with a decrease in modal value of the larger distr ibution peak and, for samples containing no drug, an increase in the p roportion of droplets in the lower size distribution. The results ther efore indicate that the drug interacts with one or more components of the self-emulsifying system, leading to a change in droplet size distr ibution which varies as a function of drug concentration.