chitosan and plga microspheres as drug delivery ... - UniCA Eprints

5. RFP Loaded Chitosan Microspheres Prepared by Spray-Drying Method10080% RFP6040200A B C D E F G HNEED%Figure 5.5: Nebulization Efficiency of the Encapsulated Drug (NEED%) of Spray-DryedMicrospheres5.2.6. Release/Stability StudiesRelease studies were carried out by using two different mediums, phosphate buffer at pH 7.4and SGF at pH 1.2, in order to evaluate the effect of pH on RFP release from chitosanmicrospheres. In Figure 5.6 and 5.7, RFP release profiles from RFP-loaded chitosanmicrospheres in both release mediums are shown. Reported values are the arithmetical meanof at list three measurements. Only dissolution profiles from formulations A and E (the moststable and with) the slowest amount of chitosan) are shown in the figure in order to betterevaluate the influence of the cross-linking agent, withoth any other variable.Rifampicin release from the chitosan microspheres is pH dependent: it is faster at pH 1.2 thanat pH 7.4. This is the consequence of the higher solubility of chitosan at lower pH, where theD-glucosamine residues are ionized resulting in an extensive polymer swelling and faster drugrelease. Moreover, rifampicin solubility is pH dependent: it increases as the pH increases. Infact, as proposed earlier, chitosan microspheres can also provide pH-responsive release profileby swelling in acidic environment of the gastric fluid. When comparing the drug releaseprofiles from cross-linked and un-cross-linked chitosan microspheres, a substantial decreaseof the release rate is obtained from the cross-linked microparticles at pH 7.4.As can be seen from the graphs, in both cases there is a significant burst effect, which is moreimportant for formulation E that in only 0.5 hours released 24 (pH 7.4) and 43% (pH 1.2) ofthe encapsulated drug while formulation A in the same period released 16 and 25% at pH 7.4and pH 1.2 respectively.Obtained results show that cross-linkage with GA can delay drug release as a consequence ofthe higher stability of the hydrogel network. In fact, in both media the cross-linked81