Sustained release of bupivacaine for post-surgical pain relief using core-shell microspheres.

Core-shell polymer microspheres with poly(d,l-lactic-co-glycolic acid) (PLGA) core and poly(l-lactic acid) (PLLA) shell were developed for sustained release of bupivacaine for postoperative pain relief after knee surgery. The PLLA-rich shell acted as a diffusion barrier, allowing linear release of bupivacaine in a goat model over an extended period of 2 weeks post-surgery. In vivo bupivacaine concentrations in the goat synovial fluid remained within therapeutic levels for the 2 weeks, whereas bupivacaine concentrations in the blood plasma remained safely below toxic levels.