Understanding excipient-induced crystallization of spray-dried amorphous solid dispersion

This study investigates the compatibility of excipients with the model system SDI-X and their role in the induced crystallization of the amorphous compound-X in tablet formulations. We aimed to establish a straightforward and practical screening approach for evaluating excipient-induced crystallization of SDI in tablet matrices. Three methodologies-binary powder mixture, binary compact, and bilayer tablets-were employed to qualitatively and quantitatively evaluate the recrystallization of SDI-X with various excipients under accelerated storage conditions. The results demonstrated that binary compacts, providing direct physical contact between SDI-X and excipients, are superior in reflecting realistic drug-excipient contact within pharmaceutical tablets, enabling a more accurate assessment of excipient-induced crystallization for SDI-X. In contrast, the broadly used conventional binary blends can significantly underestimate this risk due to insufficient proximity. In addition, the bilayer tablets further confirmed that crystallization initiates at the contact surface between SDI-X and the excipients. The study highlighted that not only hygroscopicity but also the type of excipient and its physical contact with SDI-X significantly influence the recrystallization extent and rate of SDI-X. Interestingly, less hygroscopic diluents such as mannitol and lactose induced much higher levels of crystallization of SDIs, contrary to expectations based on moisture content alone. This suggests that the excipient type and contact surface are more critical in inducing recrystallization than just the level of moisture. The findings emphasize the need for careful excipient selection, study design, and sample preparation to enable appropriate assessments of SDI-excipient compatibility.