The step-wise dissolution method: An efficient DSC-based protocol for verification of predicted API-polymer compatibility

The development of an amorphous solid dispersion (ASD) is a promising strategy for improving the low bioavailability of many poorly water-soluble active pharmaceutical ingredients (APIs). The construction of a temperature-composition (T-C) phase diagram for an API-polymer combination is imperative as it can provide critical information that is essential for formulating stable ASDs. However, the currently followed differential scanning calorimetry (DSC)-based strategies for API solubility determination in a polymer at elevated temperatures are inefficient and, on occasions, unreliable, which may lead to an inaccurate prediction at lower temperatures of interest (i.e., T = 25 degrees C). Recently, we proposed a novel DSC-based protocol called the step-wise dissolution (S-WD) method, which is both cost-and time-effective. The objective of this study was to test the applicability of the S-WD method regarding expeditious verification of the purely-predicted API-polymer compatibility via the perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state (EOS). Fifteen API-polymer T-C phase diagrams were reliably constructed, with three distinct API-polymer case types being identified regarding the approach used for the S-WD method. Overall, the PC-SAFT EOS provided satisfactory qualitative descriptions of the API-polymer compatibility, but not necessarily accurate quantitative predictions of the API solubility in the polymer at T = 25 degrees C. The S-WD method was subsequently modified and an optimal protocol was proposed, which can significantly reduce the required experimental effort.

Automated summary

The development of amorphous solid dispersion (ASD) is a promising strategy for improving the bioavailability of poorly water-soluble active pharmaceutical ingredients (APIs). However, the current differential scanning calorimetry (DSC)-based strategies for API solubility determination at elevated temperatures are inefficient and unreliable. In this study, a cost-effective and time-effective DSC-based protocol called the step-wise dissolution (S-WD) method was proposed and tested for its applicability in verifying API-polymer compatibility. The results showed that the S-WD method, when combined with the perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state (EOS), could reliably construct API-polymer temperature-composition (T-C) phase diagrams. However, the PC-SAFT EOS did not provide accurate quantitative predictions of API solubility in the polymer at lower temperatures of interest. The S-WD method was subsequently modified to reduce the required experimental effort.