Development and evaluation of ropivacaine loaded poly(lactic-co-glycolic acid) microspheres with low burst release.

The purpose of this paper was to prepare microspheres loaded with ropivacine with low initial burst release. Three different methods including double emulsion (W/O/W), solid in oil in water (S/O/W) and modified oil in water (O/W) emulsion solvent evaporation technique were used to obtain microspheres (that is microspheres A, B and C) and the O/W method was finally used to acquire microspheres with suitable particle size (11.19±1.24 µm), high drug loading (28.37±1.15 %), entrapment efficiency (98.15 %) and low initial burst release. To evaluate the in vivo pharmacokinetics, microspheres C and D were injected into rats by intravenous, intramuscular and intraperitoneal route, respectively. It was indicated that both low initial drug burst release and sustained release effect were exhibited for microsphseres C and D in spite of injection route. A linear in vitro-in vivo relationship was established after normalization of the time required to reach plateau for the in vitro and in vivo data and the in vitro release data were predictive of the in vivo release. There were good linear correlation between the in vitro and in vivo release behavior(R2= 0.9629-0.9791). The result of above proved that ropivacaine loaded microspheres may have great potential for clinical use. In conclusion, the ropivacine microspheres prepared in this paper have great potential for clinical use.