Theretical and experimental characterisation of stearic acid based sustained release devices obtained by hot melt co-extrusion

This study was conducted to develop and characterize a hot melt co-extruded cylindrical system for controlled drug delivery. Different lengths and configurations (homogeneous, hollow and heterogeneous) co-extrudates were considered. Stearic acid and polyethylene glycol were used as hydrophobic and hydrophilic components, respectively. Acetaminophen and theophylline were used as model drug. Release kinetics were studied on the basis of in vitro tests and experimental data were analyzed by a new mathematical model accounting for drug dissolution and diffusion inside the cylindrical matrix. Surface tension measurements were carried on the two model drugs and the hydrophobic matrix. Experimental results showed that co-extruded length and configuration sensibly affect release kinetics of both drugs. Additionally, the proposed mathematical model proved to be reliable and yielded an explanation for the lower acetaminophen release rate with respect to that of theophylline. This behavior could be explained by the formation of a low permeable layer surrounding the acetaminophen-loaded systems. In addition, surface property analysis evidenced the higher hydrophobic nature of acetaminophen-loaded systems with respect to theophylline systems.