Implications of particle size on the respective solid-state properties of naltrexone in PLGA microparticles

A thorough understanding of the complexities in formulating and manufacturing polymeric microspheres is required for new and generic drug applications. Specifically, for an ANDA application for polymeric microsphere-based products, the applicant must meet Q1 (qualitative) and Q2 (quantitative) sameness, and in some cases, Q3 (e.g., microstructural) sameness. Herein, we report the naltrexone crystallinity in a PLGA microparticle system prepared from a dichloromethane-benzyl alcohol solvent system results in a crystallinity dependence as a function of microparticle size from the same batch - illustrating intrabatch microstructural variability. As the particle size increases, the crystallinity increases, with additional polymorphic forms more readily noted at the large particle sizes. Furthermore, during dissolution, a polymorphic transition and/or crystallization occurs at larger size fractions. This study highlights the importance of controlling the manufacturing parameters during microparticle formation, specifically solvent extraction and particle size control. Furthermore, with the approval of generic microparticles formulations on the horizon, this study highlights the importance of Q3, the same components in the same concentration with the same arrangement of matter, whereby microparticles can have varying microstructural properties across particle sizes from the same batch.