Influence of drying procedure and of low degree of substitution on the structural and drug release properties of carboxymethyl starch.

The aim of this study was to investigate the influence of drying methods and low range of degrees of substitution (DS) on the structural, physicochemical, and drug-release properties of carboxymethyl high-amylose starch (CMS). CMS with three DS of 0.03, 0.14, and 0.25 was synthesized and dried by either solvent precipitation (SP), spray drying (SD), or lyophilization (Ly). DS had an influence on the crystalline structure of CMS. It was found that a DS of 0.14 or higher induced a modification of polymorphism. The drying method and the DS had both an impact on the physical properties of the CMS powder which can further influence the formulation characteristics and drug-release properties from monolithic tablets. The CMS with DS of 0.14 and 0.25 dried by SP or SD presented good excipient properties in terms of compressibility. With acetaminophen (20%) as tracer, the monolithic CMS tablets showed controlled drug release over 17 h for DS of 0.14 and 10 h for DS of 0.25, almost independent of pH, suggesting interesting properties for sustained release applications.