A new generation of starch products as excipient in pharmaceutical tablets . II. High surface area retrograded pregelatinized potato starch products in sustained-release tablets

A new linear short-chain starch product was prepared by gelatinization of potato starch followed by enzymatic degradation, precipitation (retrogradation) and filtration. A high specific surface area was subsequently created by washing with ethanol or acetone or freeze-drying. Tablets compressed from a mixture containing the starch product and 30% theophylline at a force of at least 15 kN showed no disintegration and an almost constant (zero-order) sustained drug release. The delivery from these non-porous tablets proved to be a swelling-controlled solvent-activated mechanism, as was confirmed by the slow penetration of a solvent front into the tablet. Drug release proved to be not affected by the incorporation of magnesium stearate into the tablet or the presence of alpha-amylase in the dissolution medium, both features in contrast to similar tablets compressed from conventional pregelatinized starches, which were prepared by gelatinization followed directly by thermic dehydration. A specific surface area of 1.5 m(2)/g proved to be a prerequisite for the starch product to control drug release. A high surface area (linear long-chain) amylose product showed a sustained but less linear release profile. Branched short and long-chain products with a high surface area produced disintegrating tablets and are therefore not able to control drug release.