Experimental Study Of Preparation And Release Characteristics Of Rifampin Microspheres

Objective:By preparing polylactic acid/glycolic acid (PLGA)-Rifampin(RFP)Microspheres(Ms), we researched the diameter, encapsulation efficiency, drug loadingrate and release characteristics in vitro of the microspheres,meanwhile,after implantingPLGA-RFP microspheres into the paraspine of rabbits, we observed local the tissueconcentrations of RFP and burst release and sustained release characteristics ofPLGA-RFP microspheres, at the same time,we would research the release characteristicsof PLGA-RFP microspheres in vivo, so we could absolutely understand the role and thepotential application of RFP microspheres in the treatment of spinal tuberculosis, in orderto make an experimental basis for the other upcoming experiments and clinicalapplications.Methods and Results:Methods:(1) using emulsion solvent evaporation method (W/O/W) to prepare PLGA-RFP Microspheres;(2) considering encapsulation efficiency, drug loading rate andrelease evaluation index in vitro as indicators, we researched the influence of singlefactor,such as PLGA average molecular weight (Mw), colostrum preparation methods,stirring rate, the volume of the aqueous phase and so on, on the diameter, encapsulationefficiency, drug loading rate and release characteristics in vitro of the Ms, in order tooptimize the best method for preparing the Ms;(3) using UV spectrophotometer tomeasure the rifampicin drug loading rate and encapsulation efficiency of PLGA-RFP Ms;(4) using a scanning electron microscope to observe the morphological observation ofPLGA-RFP Ms,the measurement of particle size and its distribution;(5) using PBS asthe release medium,we observe the stable condition of PLGA-RFP Ms at differenttemperatures, and study its release characteristics in vitro;(6) Applicating highperformance liquid chromatography (HPLC) to establish a standard curve of RFP,so wecould measure the concentrations of RFP in the plasma and other tissues;(7) firstly wegrooved the bone of rabbit paraspine, secondly we implantd the PLGA-RFP Ms into theparaspine of the rabbit,and then we could research release characteristics of PLGA-RFPMs in vivo. Results:(1) PLGA-RFP Ms have a round shape, smooth surface, and the orange-redcolour;(2) optimized prescription:1:1PLGA503H (Mw65000) and PLA200mg, wasdissolved in2ml of dichloromethane, and then added a saturated solution of1%PVA in20ml,400rpm stirring for20min, then transferred to100ml0.2%PVA saturated solution,600rpm stirring volatile solvent4h;(3) the RFP drug loading rate of PLGA-RFP Ms was42.95%, the encapsulation efficiency was87.83%;(4) the particle size distribution of theMs was approximately normally distributed, and an average particle size of PLGA-RFPMs were124um;(5) the release characteristics in vitro of the PLGA-RFP Ms: the releasecharacteristics in vitro of MS was zero order mode, the burst rate after24h was less than25%, the release rate of two weeks was up to81%;(6) the release characteristics in vivoof the PLGA-RFP Ms: After RFP Ms and RFP was implanted into the bone of the rabbitlumbar vertebrae,the concentrations of RFP in the6thlumbar vertebrae and the muscle canmaintain at the level of concentration of the minimum inhibitory concentration (MIC)above until after28d of the opearation, but the rifampicin concentrations of the RFP Msgroup in the6thlumbar vertebrae and the muscle decreased smoother than the RFP group,and could contiue longer，while the liver and other tissues had no significant accumulation.Conclusion:(1) PLGA-RFP Ms which used the method of emulsion solvent evaporationmethod (W/O/W) had an average particle size of124um, and the appearance evaluation,drug loading, encapsulation efficiency, and other indicators of PLGA-RFP Ms were fine;(2) an appropriate proportion of dosing ratio, the aqueous phase volume, stirring speed,carrier material, had great impact on the encapsulation efficiency, drug loading rate andrelease behavior of PLGA-RFP Ms;(3) the release characteristics in vitro of MS wassmooth, the burst rate after24h was low, the release cycle was long;(4) After RFP Mswas implanted into the bone of the rabbit lumbar vertebrae,the concentrations of RFP inthe6thlumbar vertebrae and the muscle can maintain at the level of concentration of theminimum inhibitory concentration (MIC) above until after28d of the opearation, and thelocal RFP concentration could decrease smoothly and contiue longer, while the liver,lungs and other tissues had no significant accumulation.