Controlled‐release formulations for hydroxy urea and rifampicin using polyphosphate‐anion‐crosslinked chitosan microspheres

Abstract

AbstractPhysically crosslinked microspheres for the controlled delivery of rifampicin and hydroxy urea have been prepared with sodium tripolyphosphate (STPP) and sodium hexametaphosphate (SHMP) anion crosslinkers. Chitosan with a constant degree of deacetylation (75 wt %) and a constant molecular weight (1134 kg/mol) has been found to be useful for the controlled release of selected drugs. The microspheres prepared with the SHMP anion crosslinker are more hydrophobic and compact in their shape and size than the microspheres prepared with the STPP anion crosslinker. The SHMP‐anion‐crosslinked microspheres show optimum loading at pH 3, whereas the STPP‐anion‐crosslinked microspheres show optimum loading at pH 4. The STPP‐anion‐crosslinked microspheres are suitable for the controlled release of rifampicin, but the SHMP‐anion‐crosslinked microspheres are suitable for the controlled release of hydroxy urea. The drug‐release characteristics of the physically crosslinked chitosan microspheres are explained with respect to their size and the ionic interactions of the encapsulated drugs with the polymer matrices and anion crosslinkers. The initial burst release of the loaded drugs is Fickian in nature and follows first‐order kinetics, but the controlled step of the drug release shows a non‐Fickian nature and follows zero‐order kinetics. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1942–1956, 2007