Theoretical and experimental study on theophylline release from stearic acid cylindrical delivery systems

The purpose of this study is to evaluate the possibility of developing a cylindrical sustained-release dosage form for theophylline directly by means of a ram extrusion process. In particular, the formulations contained: stearic acid as a low melting binder, monohydrate lactose and polyethylene glycol 6000 as hydrophilic fillers. The influence of type and percentage of the components was studied considering different parameters such as the time required for 50% of the drug release (t50%)and the drug diffusion coefficient in the delivery system. The choice of the different formulations to be tested is carried out employing an axial design with constraint domains. The limits of each component were fixed on the basis of preliminary trials. The analysis of the t50% values revealed that the release kinetics is mainly affected by stearic acid and theophylline content, whilst lactose effect is almost negligible. A substantial correspondence between the experimental results and the analysis of the drug release kinetics performed by means of an ad hoc developed mathematical model was found. The proposed mathematical model allows to conclude that wherever the release mechanism is initially ruled by dissolution, then diffusion plays the most important role.