Emerging role of primary heterogeneous nucleation in pharmaceutical crystallization

Crystallization is an important and difficult to control unit operation in the pharmaceutical industry. Crystallization can control molecular (i.e., polymorphism) and particulate (i.e., particle size and crystal habit) properties of active pharmaceutical ingredient (API). Moreover, these molecular and particulate properties govern the manufacturability, stability, and biopharmaceutical performance of the API and drug product. Nucleation is a key step and primary heterogeneous nucleation is a common mode of nucleation during crystallization. Hence, it is important to understand the parameters affecting primary heterogeneous nucleation, to achieve desirable properties in crystalline APIs. Primary heterogeneous crystallization has usually been linked to the surface characteristics like topography and functionality of the heteronucleant. The review outlines recent findings in the primary heterogeneous crystallization with specific emphasis on its pharmaceutical applications including regulatory considerations. Molecular-level mechanisms governing heteronucleation and subsequent outcome in terms of molecular as well as particulate-level properties of API have also been discussed. Moreover, general guidance for the selection of heteronucleant has also been included. Heterogeneous crystallization is a promising tool for efficient crystallization of API having properties for optimal pharmaceutical performance.

Microfluidic Particle Engineering of Hydrophobic Drug with Eudragit E100─Bridging the Amorphous and Crystalline Gap

Co-processing active pharmaceutical ingredients (APIs) with excipients is a promising particle engineering technique to improve the API physical properties, which can lead to more robust downstream drug product manufacturing and improved drug product attributes. Excipients provide control over critical API attributes like particle size and solid-state outcomes. Eudragit E100 is a widely used polymeric excipient to modulate drug release. Being cationic, it is primarily employed as a precipitation inhibitor to stabilize amorphous solid dispersions. In this work, we demonstrate how co-processing of E100 with naproxen (NPX) (a model hydrophobic API) into monodisperse emulsions via droplet microfluidics followed by solidification via solvent evaporation allows the facile fabrication of compact, monodisperse, and spherical particles with an expanded range of solid-state outcomes spanning from amorphous to crystalline forms. Low E100 concentrations (≤26% w/w) yield crystalline microparticles with a stable NPX polymorph distributed uniformly across the matrix at a high drug loading (∼89% w/w). Structurally, E100 incorporation reduces the size of primary particles comprising the co-processed microparticles in comparison to neat API microparticles made using the same technique and the as-received API powder. This reduction in primary particle size translates into an increased internal porosity of the co-processed microparticles, with specific surface area and pore volume ∼9 times higher than the neat API microparticles. These E100-enabled structural modifications result in faster drug release in acidic media compared to neat API microparticles. Additionally, E100-NPX microparticles have a significantly improved flowability compared to neat API microparticles and as-received API powder. Overall, this study demonstrates a facile microfluidics-based co-processing method that broadly expands the range of solid-state outcomes obtainable with E100 as an excipient, with multiscale control over the key attributes and performance of hydrophobic API-laden microparticles.

Control of Drug-Excipient Particle Attributes with Droplet Microfluidic-based Extractive Solidification Enables Improved Powder Rheology

PURPOSE

Industrial implementation of continuous oral solid dosage form manufacturing has been impeded by the poor powder flow properties of many active pharmaceutical ingredients (APIs). Microfluidic droplet-based particle synthesis is an emerging particle engineering technique that enables the production of neat or composite microparticles with precise control over key attributes that affect powder flowability, such as particle size distribution, particle morphology, composition, and the API's polymorphic form. However, the powder properties of these microparticles have not been well-studied due to the limited mass throughputs of available platforms. In this work, we produce spherical API and API-composite microparticles at high mass throughputs, enabling characterization and comparison of the bulk powder flow properties of these materials and greater understanding of how particle-scale attributes correlate with powder rheology.

METHODS

A multi-channel emulsification device and an extractive droplet-based method are harnessed to synthesize spherical API and API-excipient particles of artemether. As-received API and API crystallized in the absence of droplet confinement are used as control cases. Particle attributes are characterized for each material and correlated with a comprehensive series of powder rheology tests.

RESULTS

The droplet-based processed artemether particles are observed to be more flowable, less cohesive, and less compressible than conventionally synthesized artemether powder. Co-processing the API with polycaprolactone to produce composite microparticles reduces the friction of the powder on stainless steel, a common equipment material.

CONCLUSIONS

Droplet-based extractive solidification is an attractive particle engineering technique for improving powder processing and may aid in the implementation of continuous solid dosage form manufacturing.

Kinetic Retraction at the Onset of Concomitant Crystallization and Implication on Polymorphic Formation

The four-quadrant regimes of attainable polymorph crystallization (FQR-APC) plot was recently developed through numerical simulations of crystallization kinetics of a dipolymorphic system. Retraction in the polymorphic composition of the most stable form in crystallized samples was unveiled a characteristic indication of concomitant polymorphism. Comparisons were made with a recently developed concept, the Ostwald ratio (OR), in light of characterization of polymorphic formation. It was shown that both schemes display a good agreement in describing polymorphic outcomes, despite their distinct theoretical origins.