Investigation of pharmaceutical oil/water microemulsions by small-angle scattering

Purpose. Stable oil/water (o/w) microemulsions are very effective vehicle systems for dermal administration of drugs having no or low skin penetration. These systems, consisting of oils, a blend of a high and a low HLB surfactant, and a hydrophilic phase (propylene glycol/water), were developed using pharmaceutically acceptable components. Methods. In this paper, the droplet size of these microemulsions was characterized by means of dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Furthermore, different size parameters obtained by DLS and SANS experiments were compared and discussed. Results. Extremely small droplet radii of approximately 10 nm could be observed. A good agreement between the data of DLS and SANS experiments was found. The kind of oil only marginally influences the droplet size. Conclusions. Particle size determination via scattering techniques is a useful tool to characterize droplets in microemulsions for dermal drug delivery.