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.
