Preparation and evaluation of sodium carboxymethyl starch as suspending agent

Abstract

Four domestically available starches, including tapioca starch, rice starch, glutinous rice starch, and corn starch, were chemically modified and evaluated for their properties as suspending agent. Sodium carboxymethyl starches with three different degrees of subsitution (DS) were prepared from the reaction between native starches and monochloroacetic acid in NaOH. The prepared modified starches were subjected to the preliminary selection for the best modified starch from each type. The selection was made based on the viscosity of dispersion of modified starch and on the sedimentation volume (SV) and the redispersibility of calcium carbonate suspension containing modified starches. Modified starches being selected were modified glutinous rice starch (MGS), modified rice starch (MRS), and modified tapioca starch (MTS) with DS of 0.16, 0.26, and 0.38, respectively. Modified corn starch (MCS) was excluded from the study after preliminary evaluations due to its poor viscosity, sedimentation volume, and redispersibility. Selected modified starches were then evaluated for their suspending property in ibuprofen suspension, in comparison with six commonly used suspending agents-Xanthan Gum (XG), Avicel RC-591 (AV), Sodium Alginate (SA), Acacia (AC), Tragacanth (TG), and Sodium Carboxymethylcellulose (SCMC). The evaluation parameters included SV, rheology, redispersibility, and uniformity of drug dispersion during storage. The results suggested that MRS and MTS were promising suspending agent. Suspensions containing as low as 1% MRS and MTS possessed high viscosity and sedimentation volume, good redispersibility and uniformity of drug dispersion during storage. The results are comparable to those of XG and SCMC and are much better than those of AV, AC, SA, and TG. The use of MGS as suspending agent was limited by its incompatibility with a component in the formulation, tween 80, which resulted in rapid sedimentation of suspension. Considering the amounts of rice starch and tapioca starch produced in Thailand annually, MRS and MTS are good candidates for the development as new, low-cost suspending agents.