Predicting Solubility/Miscibility in Amorphous Dispersions: It Is Time to Move Beyond Regular Solution Theories.

Area of Science:

• Pharmaceutical Science
• Materials Science
• Physical Chemistry

Background:

• Poorly soluble drugs present formulation challenges, necessitating advanced solubilization techniques.
• Amorphous solid dispersion (ASD) technology enhances oral bioavailability through drug supersaturation.
• Physical stability of ASDs is critical, driving the need for predictive crystallization methodologies.

Purpose of the Study:

• To evaluate the applicability of regular solution theory (e.g., Flory-Huggins) for predicting miscibility in hydrogen-bonded drug-excipient systems.
• To highlight the limitations of existing models in accurately assessing the physical stability of amorphous solid dispersions.
• To advocate for the adoption of more sophisticated models that account for specific interactions.

Main Methods:

• Analysis of hydrogen-bonded alcohol-alkane solutions using regular solution theory.
• Exploration of the Flory-Huggins chi (χ) interaction parameter trends and interpretation pitfalls.
• Review of existing literature on drug-polymer miscibility models.

Main Results:

• Regular solution theory, while widely used, may not be suitable for hydrogen-bonded systems common in pharmaceuticals.
• The interpretation of the Flory-Huggins χ parameter can be misleading for systems with specific interactions like hydrogen bonding.
• Current models may overestimate or underestimate miscibility, impacting stability predictions.

Conclusions:

• Existing models based on regular solution theory have significant limitations for predicting miscibility in hydrogen-bonded amorphous solid dispersions.
• Accurate prediction of physical stability requires models that explicitly incorporate specific intermolecular interactions.
• Further research into advanced modeling approaches is crucial for developing stable and effective amorphous solid dispersions.