Characterization of a crosslinked high amylose starch excipient

a controlled release excipient based on sodium trimetaphosphate (STMP) cros slinked high amylose starch has been examined by C-13 CP/MAS NMR. The dry e xcipient powder is pressed to a hard tablet whose volume increase in H2O ru ns parallel to the STMP concentration used. The known polymorph resonances of single helix 'V' starch (hydrated) and double helix 'B' starch (hydrated ) both contribute to the spectrum corresponding to the swollen tablet. The wet tablet when loaded with a pharmaceutical agent provides a near zero-ord er release profile for up to 20 h. The swelling and drug release behaviour is explained in terms of self-assembly of the STMP treated starch nanomolec ular particles. These particles are drawn together by "self-assembly" due t o formation of amylose double helices as water penetrates the tablet. An op timum level of chemical crosslinking ensures the integrity of the swollen t ablet whose sponge-like structure enclosed by a membranous surface is respo nsible for sustained release. (C) 1999 Elsevier Science B.V. All rights res erved.