Processing impact on the performance of amorphous solid dispersions
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The level of understanding of amorphous solid dispersions has grown significantly in the last two decades. A number of commercial amorphous solid dispersions have been approved and they have become the industry norm for overcoming poor water-solubility when an enabling technology is necessary. Despite their success, there are still challenges in developing high performing amorphous solid dispersions. The impact of processing technique on the quality of the resultant amorphous solid dispersion is an area that is not well understood. Spray drying and melt extrusion are the two dominant manufacturing techniques for preparing amorphous solid dispersions. The mechanism for the formation of an amorphous solid dispersion from each process is very different. Therefore, the resulting material can have different properties which contribute to the overall performance of the amorphous solid dispersions. A better understanding of processing impact is necessary. Another challenge in the development of amorphous solid dispersions is the limitation to process high melting point drug substances that also have limited organic solvent solubility. For these substances, spray drying cannot be used, and at the high temperatures required to dissolve the drug in the polymer carrier, there is significant degradation during melt extrusion. Strategies such as plasticizer, supercritical fluids, and polymer selection for melting point suppression have been used in the past but have limitations. This research focuses on the impact of the processing technique on the physical and chemical stability of the resultant amorphous solid dispersions as well as the resultant dissolution performance. This work showed that based on its mechanism of formation, melt extrusion can have an advantage when preparing a high potency amorphous solid dispersion with a fast crystallizing drug. Due to the high level of mixing in the extruder and higher temperature, a more homogeneous and thermodynamically stable amorphous solid dispersion can be prepared. Spray drying, in contrast, can produce a higher drug loading amorphous solid dispersion, however, the material is less homogeneous and physically unstable. Additionally, through process and formulation understanding, a previously deemed “un-extrudable” drug substance was successfully processed by melt extrusion. This process was also successfully scaled from lab to pilot scale equipment.