Modification Of Aspirin By Dextran And In Vitro Release Study

In this paper, dextran was used to control the crystallization process of aspirin (ASA) and prepare ASA microcrystal with uniform diameter and regular surface. FTIR, XRD and DSC analysis showed that a new kind of crystal structure of ASA microcrystal was formed in this system. Melting temperatures (Tm) of this kind of microcrystal is 139.67℃, which is 2 42℃ higher than that of ASA crystal. The average diameter of microcrystalline ASA prepared in 0.81% dextran aqueous solution was 11 06μm. The particle size increased with the decline of solution concentration. The in vitro release showed a clear enhancement in dissolution rate of ASA microcrystal. Therefore, the microcrystals are suitable for enhancing drug dissolution of hydrophobic drugs.In addition, different preparation methods for dextran microspheres (DM) have been studied. DM prepared in W/O microemulsion had uniform morphology and narrow diameter distribution, nearly 92% of them having a diameter of 56.6μm. It was found that DM had good adsorbability of ASA, the entrapping efficiency of DM in entrapping method can amount to 96.97% and that in adsorption method was 87.53%. In vitro evaluation of drug-loaded DM shows they had good property of sustained release.Finally, dextran-ASA conjugate has been prepared by a coupling reaction between acetoxybenzoyl chloride and dextran. This structure was characterized with FTIR, ~1H-NMR and ~13C-NMR. The drug-loading ratio was about 9.30% and converting efficency was about 3.07%. In vitro release study showed that this conjugate had a linear release of ASA vs time with no abrupt release and the release rate was nearly zero order. The release rate enhanced with the increase of drug-loading ratio. The release rate in artificial gastric juice was lower than that in artificial intestinal juice. It shows that dextran-ASA conjugate is stable in the acid environment of stomach, which may lead to less side-effect and reliefing stimulation of ASA on gastrointestinal (Gl) tract. What's more, the dextran-ASA conjugate has a sustained release of ASA.