Studies On PLGA Microspheres Containing Methotrexate For Intra-articular Injection

In this article, we prepared methotrexate (MTX) loaded poly (DL-lactide-co-glycolide) (PLGA) microspheres for intra-articular administration. The drug releaseprofile in vitro and in vivo, pharrnacokinetic, pharmacodynamics and biocompatibilityof the microspheres were studied.Microspheres were prepared by Oil-in-Water emulsion solvent evaporationmethod. The drug concentration was assayed by high performance liquidchromatography(HPLC). The optimal formulation was verified by orthogonal design.The surface morphology, size distribution, drug loading content and the encapsulationefficiency of different molecular weight microspheres were investigated andevaluated.Considering the difficulty of analysing the concentration of MTX in animal'sjoint cavity, a rat air-pouch model which can simulate inflammatory synovial fluidwas utilized to determine the drug release properties in vivo. The drug release rateconstant of microspheres in vivo was 0.12μg/(mL·d). Pharmacodynamical tests in ratair-pouch synovitis model showed MTX-PLGA microspheres could reduce thevolume of exudation, neutrophil count and protein contents.in exudation. Comparedwith MTX solution, MTX-PLGA microspheres have anti-inflammatory effect.A HPLC analysis method was developed to investigate the distribution of MTXinto plasma. The methodology of HPLC analysis in rabbits plasma was studied. Thepharmacokinetic of MTX following intra-articular injection of MTX-PLGAmicrospheres or MTX solution in rabbits was studied. The results showed that theclearance of free MTX from knee joint of the rabbits was rapid, the plasma MTXconcentrations reached a maximum 15min after the injection(C_max=22.25μg/mL) andwas below the limit of quantitation of the assay(0.03μg/mL) 8h after the injection. Onthe contrary, the plasma MTX concentrations of those rabbits injected withMTX-PLGA microspheres plateaued between 15min～24h. The difference of meanresidence time between two treatment groups shows that the MTX-PLGA microspheres have a sustained-release property.In the biocompatibility study, micrographs of pathological section of synovialtissues following intra-articular injection with MTX-PLGA microspheres indicatedthat microspheres were biocompatibleo The microspheres was steady in heat andhumidity but unsteady in light, and the microspheres should be conserved away fromlight.