Utilization of enzyme-resistant starch to control theophylline release from tablets

The effect of enzyme-resistant starch (RS) on theophylline release from compacted tablets made of pregelatinized waxy maize starch (PS) was investigated. The PS and RS mixtures containing theophylline (30%) were compacted to tablets by compression (60 kN), and were subsequently treated in dissolution media containing a pancreatic aamylase. The swelling ratio, resistance to erosion, and drug release properties of the tablets were measured. Rheological properties of the tablet hydrogel produced by swelling were also examined. The hydrogels exhibited a higher storage modulus (G') than loss modulus (G'), and the viscosity of the hydrogels increased by adding RS. Resistant starch helped the formation of a strong gel network which was resistant to erosion. The porosity of the tablet and hydrogel decreased with the elevation of RS content, supporting the rheological data. However, the swelling ratio of the tablets containing RS was higher than that of the tablet containing only PS. During the initial stage of dissolution up to 1 h, RS appeared suppressing the erosion possibly due to the increased resistance to enzymatic hydrolysis by RS. After 1 h, however, the erosion proceeded at higher rates than that of pure PS, possibly due to the poor compactibility of RS. Comparing the different mixtures of RS and PS, the theophylline release was most effectively retarded when RS was added to the tablet at an equivalent amount of PS.