Thermal characterization of poly(lactide-co-glycolide) microspheres containing bupivacaine base polymorphs

Solid-state chemistry of bupivacaine base, obtained by precipitation from bupivacaine hydrochloride solutions with ammonia, was investigated. Two bupivacaine base polymorphs (Form I: T-m= 105.6+/-0.0degreesC; Form II: Tm=97.6+/-0.2+/-degreesC) were isolated depending on the precipitation conditions and characterised by thermal analysis and FTIR spectroscopy. No weight loss was evidenced by TG confirming that no solvate formation had occurred. Biodegradable poly(lactide-co-glycolides) microspheres containing bupivacaine base were prepared by spray-drying. In the microspheres bupivacaine base was present as the metastable low melting crystal form independently of the bupivacaine base poly(lactide-co-glycolides) ratio.