Drug diffusion from disperse systems with a hydrophobically modified polysaccharide: Enhancer® vs Franz cells

This study assesses the capacity of a new hydrophobically modified polysaccharide –hydroxypropyl cellulose–methyl methacrylate – to control drug release in semisolid formulations. The dispersed systems contain the new polymer, Igepal® CO520 as surfactant and theophylline as model drug at three concentrations (0.5, 1 and 1.5%, w/w). Drug release study shows that the systems containing 0.5% (w/w) of drug have faster release and higher diffusion coefficient than the other two concentrations. These results can be explained by two different structures (“relaxed” and “structured”) found from a rheological point of view. Also, this paper compares two different devices for testing drug release and diffusion. It has been obtained more reliable and reproducible results with Enhancer Cell® respect to Franz diffusion cell. In both cases, Fickian diffusion was the mechanism predominant for all systems. Finally, the utility of this polymer has been demonstrated to make three-dimensional gel structure and control theophylline release from systems in topical application.