Incorporation of water-soluble drugs in PLGA microspheres

Poly(lactide-co-glycolide) (PLGA) microspheres containing blue dextran, as a model of water-soluble drugs, were prepared from w1/o/w2 emulsions by using a microhomogenizer and a solvent evaporation method. Effects of preparation conditions, such as, concentration of poly(vinyl alcohol) (PVA) in w2 phase, viscosity of inner soluble water phase, volume ratio of oil phase to w1 phase in primary emulsion, PLGA concentration in oil phase, and molecular weight or composition of PLGA, upon the properties of PLGA microspheres containing water-soluble drugs were examined. Concentration of poly(vinyl alcohol) (PVA), the dispersant dissolved in w2 phase of secondary emulsion did not show any effects on the final particle size. On the other hand, volume ratio of oil phase to water one in primary emulsion affected the final particle size, which seemed to be related to the local PLGA concentration in w1/o emulsions. That is, the particle size increased as the volume ratio of w1 phase against oil phase, w1/o (v/v), increased. The loading efficiency, however, was not affected by the volume ratio of w1/o (v/v), but affected by blue dextran concentration in w1 phase. Higher loading efficiency was observed in PLGA microspheres prepared from w1 phase containing lower concentration of blue dextran. Blue dextran solution (inner water phase) with the lower viscosity may result in the lower leakage ratio of blue dextran during the preparation procedure. Increases in concentration and molecular weight of PLGA made particle size larger.