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

4. RFP Loaded Chitosan Microspheres Prepared by Precipitation Method5040% RFP3020100Form.0Form.1Form.2Form.3Form.0GForm.4Form.5Form.6NEED%NEED% After FDFigure 4.6: Nebulization Efficiency of The Encapsulated Drug (NEED%) Before andAfter Freeze-Drying4.2.6. Release/Stability StudiesRelease studies were carried out by using three different release media. Phosphate buffer atpH 7.4 and acetic acid buffer at pH 4.4 were used in order to evaluate the influence of the pHinside phagosome and lysosome on RFP release from chitosan microspheres. In Figure 4.7and 4.8, RFP release profiles from RFP-loaded chitosan microspheres at pH 4.4 and 7.4 buffersolutions respectively, are shown.As can be seen from the figures, an initial burst effect was observed from all chitosanmicroparticles (between 19 and 30% of loaded RFP). After this initial burst, all studiedmicrospheres released RFP at a lower rate. RFP release from the was pH dependent (fasterrelease at pH 4.4 than at pH 7,4). This is attributed to the higher solubility of the polymer atlower pH. In fact, as proposed earlier (258), chitosan microspheres can also provide pHresponsiverelease profile by swelling in acidic environment of the gastric fluid. Whencomparing the release profiles from cross-linked (with GA) and uncross-linked chitosanmicrospheres, we see that at pH 7.40 the release of RIF is substantially decreased in the crosslinkedparticles. It has been proposed before that GA addition in chitosan particles can beused as a method to modulate release kinetics of drugs, as demonstrated for theophylline(259). However, the difference between the release kinetics of RFP from the two types ofchitosan particles is more or less diminished (or is a lot smaller) at pH 4.40, possibly due tothe rapid swelling and increased solubility of this polymer at low pH, which results in a veryfast release of particle- loaded RFP from all chitosan microspheres during the first 8 hours ofincubation.65