Controlling polymorphism of carbamazepine nanoparticles in a continuous supercritical-CO2-assisted spray drying process

Controlling polymorphism in the transition from batch to continuous crystallization represents a major obstacle for the pharmaceutical industry. This work demonstrates a novel methodology to control the polymorphism of carbamazepine (CBZ) nanoparticles, a highly polymorphic BCS class II drug, using a continuous supercritical CO2 antisolvent-assisted nano spray drying (SASD) process. We show herein that when supersaturation conditions are achieved in the high-pressure SASD nozzle in the presence of anionic additives (e.g. sodium stearate, sodium dodecyl sulfate), nanoparticles of the metastable CBZ form II (using sodium stearate) or the stable CBZ form III (using sodium dodecyl sulfate) are obtained from methanol solutions, respectively. This novel methodology provides control over the final polymorphic form of CBZ obtained by (1) templating the desired polymorphic form when supercritical CO2 supersaturates the CBZ-additive methanol solution in the nozzle and (2) avoiding/minimizing the occurrence of any possible polymorphic transformation by immediately spray drying the supercritical antisolvent induced suspension into a dried fine powder. These results contrast with those obtained when using non-supersaturating conditions in the SASD nozzle (amorphous CBZ is obtained, regardless of the additive used) and when using conventional spray drying (SD) where there is no antisolvent effect in the nozzle (CBZ form IV is obtained, regardless of the additive used). The impact that the mass ratio of methanol and supercritical CO2 has on the supersaturation and consequently on the polymorphic outcome of carbamazepine obtained from batch and continuous supercritical CO2 antisolvent crystallization processes is also discussed.