Crosslinked Starch as Sustained Release Agent

Different types of crosslinked starches and pregelatinized-crosslinked starches were evaluated for their use as hydrophilic matrices. Some fundamental properties of these chemically modified starches, e.g. granule swelling power and viscosity of the dispersion in function of pH and ionic strength, were studied. Dissolution tests and the rate and amount of water uptake were evaluated on tablets containing theophylline and modified starch (40/60 w/w), compressed on an instrumented tablet press at three different pressures (50,200 and 300 MPa.). Theophylline releasing profiles were determined using the paddle system at a rotational speed of 50 rpm Water, simulated gastric fluid, and simulated intestinal fluid were used as dissolution media. Crosslinked starches showed a poor swelling power and dispersion viscosity in comparison to pregelatinized starch and pregelatinized-crosslinked starches. The pregelatinized-crosslinked starches developed less swelling power than the pregelatinized starch, but they showed higher dispersion viscosity than the pregelatinized starch. The viscosity of all starch dispersions was not affected by ionic strength. An alkaline pH dramatically increased the dispersion viscosity of pregelatinized starch and pregelatinized-crosslinked starches. Drug dissolution rate was lower for tablets containing pregelatinized starch than for tablets containing pregelatinized-crosslinked starches. This phenomenon can be related to the rate and amount of water uptake. The dissolution rate seemed not to be influenced by the compression force nor by the composition of the dissolution media. The results indicate that crosslinked starches, either pregelatinized or not, are not suitable as sustained release agents.