The impact of product quality attributes on in vivo performance of bupivacaine multivesicular liposomes.

A bupivacaine multivesicular liposomal injectable formulation, Exparel™, is a nonopioid long-acting local analgesic indicated for pain management across and/or post surgeries. For such products, preclinical data is lacking to support bioequivalence determination for potential generic products. Therefore, in the present work, in vivo studies were set up in male Sprague-Dawley rats to understand the in vivo performance of bupivacaine multivesicular liposomes (MVLs), aiming to provide information on bioequivalence establishment between comparator products. Bupivacaine MVLs show a multiphasic release profile, and their pharmacokinetics (PK) may differ with different experimental conditions including doses, administration routes, and sample dilution factors. In this work, compromised bupivacaine MVLs were either generated in lab by freeze-thawing, mechanical agitation, and high-temperature incubation, or chosen from years-old expired batches of Exparel™, for a preliminary investigation on the in vitro and in vivo association. The formulation attributes of different bupivacaine MVLs were characterized, including morphology, particle size distribution, formulation pH, free drug contents, in vitro release, and in vivo PK. In the rat study, even with an observation of inter- and intra-variability in PK, an association between product attributes and in vivo behaviors was demonstrated with bupivacaine MVLs. Overall, investigating the bupivacaine MVLs in vivo is beneficial not only to fill in gaps in preclinical data in the field of bupivacaine MVLs, but also to help pave the path for developing other MVL-related products.