Excipients play a great role in ensuring that pharmaceutical dosage form meets the required specifications of quality approved by the relevant authorities. Starches are the most widely used excipients in dosage form development, but their use is enhanced by several modification methods (such as chemical degradation, physical alteration, enzymatic modifications or crystalline-genetic transformation), all aimed at restructuring the starch granules, thus ensuring that the reactive polymers are accessible to reactants. Chemical modification of starch usually follows the pathway of substitution, degradation or cross-linking. The most common approaches to chemical modification of starches for pharmaceutical use include oxidation, esterification and etherification, which are employed to optimize the structural and nutritional properties for targeted applications. The oxidant type, botanical origin of starch, and process conditions are all determinants of how effective the oxidation is. Esterification improves the hydrophobicity of starch usually via acetylation and phosphorylation, while etherification is a derivatization technique that involves the use of various alkylation agents such as dimethyl sulphate, diethyl sulphate, alkylene oxides (epoxides) and alkyl halides. Chemically modified starch enhances thermoplasticity, solubility and flow properties. In conclusion, chemically modified starches have shown excellent potentials and are, thus, incorporated as core excipients in several pharmaceutical drug formulations.
Part of the book: Chemical Properties of Starch