In Vitro Characterization of Polyorthoester Microparticles Containing Bupivacaine

Abstract

Laboratory-scale spray-congealing equipment was utilized to fabricate injectable microparticles consisting of polyorthoester and bupivacaine. Operating conditions for the spray-congealing process were optimized to produce microparticles with the desired shape and particle size to yield acceptable syringeability and injectability. Characterizations were performed to determine the chemico-physical properties of polyorthoester before and after microparticle fabrication. Microparticles with different drug loadings and comparable particle sizes were produced, and their in vitro drug-release profiles were determined. The in vitro drug release of microparticles with a high drug loading was markedly faster than those with a low drug loading. This is partially attributed to a more significant initial burst–drug release of the microparticles with a high drug loading. The microparticles have demonstrated the potential to be used for long-acting postsurgery pain management by local injection.

Keywords:

• Spray congealing
• Injectable microparticles
• Polyorthoester
• Bupivacaine
• Particle size
• Syringeability
• Injectability
• In vitro drug release
• Initial burst–drug release
• Long acting