Drug release from hydrogel-based matrix systems partially coated: experiments and modeling

Hydrogel-based matrix systems are largely used as controlled drug delivery systems, since it is possible to get the desired drug release profile properly designing the system in term of composition, drug loading and shape. Meanwhile, the mathematical modeling of the phenomena involved in the drug release process is a useful tool to understand and to predict the complex behavior of these systems, in term of water up-take, matrix swelling and erosion, drug diffusion and release. Furthermore, the coating of the matrix is used to provide certain characteristics such as enteric resistance, meanwhile making more complex the mathematical description of the process. In this work cylindrical tablets made of hydroxyl-propyl-methyl-cellulose (HPMC) loaded with theophylline (TP), as obtained or coated by an impermeable painting on the lateral surface were dissolved in a USP II apparatus, and the release of TP, as well as of HPMC and the shape changes were monitored in time, for several rotational speeds of the impeller. The experimental data gathered were used to tune a previously proposed mathematical model. The model was found able to correctly describe all the observed phenomena, confirming its usefulness as a tool in design and production of pharmaceutics.