Hydroxypropylated starches of varying amylose contents as sustained release matrices in tablets

Waxy corn, Hylon VII, and common corn starches were hydroxypropylated to low and high levels, and their sustained release properties and matrix characteristics were studied. Hydroxypropylation had a stronger impact on Hylon VII and common corn starch matrices than on waxy corn ones, suggesting that the behavior of starch tablet was dominated by its amylose content. The introduction of hydroxypropyl groups increased the water holding capacity of all starches and resulted in more fluid-like and softer matrices with increased chain mobility for amylose-containing starches. There was a decrease in the tablet porosity and in the storage modulus of swollen tablets of Hylon VII and common corn starches after hydroxypropylation. Microscopic analyses revealed smoother and less porous tablet structure upon hydroxypropylation of all starches. Hydroxypropylation improved the sustained release ability of amylose-containing starch matrices, and conferred additional resistance to the hydrolytic action of pancreatin under simulated gastrointestinal conditions. However, hydroxypropylation had a detrimental impact on drug release from waxy corn starch matrices.