Utilization of retrograded waxy maize starch gels as tablet matrix for controlled release of theophylline

Theophylline tablets were prepared using waxy maize starch gels and the effect of retrogradation on the release of theophylline was investigated. Slurries of starch and theophylline were autoclaved in a polypropylene tablet mold and then stored at 4 °C or cycled at 4/30 °C for 8 days. By increasing the period of retrogradation at 4 °C the size of air cells in freeze-dried gels was decreased and the cell walls became thinner. Retrogradation reduced the pore size of the gels and hindered gel swelling in an amylase-containing dissolution medium. These effects became more significant with temperature cycles. The resistance to enzymatic erosion and decreased swelling by the retrogradation under 4/30 °C cycles resulted in a retarded release of theophylline. Thus, temperature-cycled retrogradation of a waxy maize starch gel provided a compact matrix structure that effectively retarded the drug release.