Trends in solubility of polymorphs.

Area of Science:

• Pharmaceutical Science
• Physical Chemistry
• Materials Science

Background:

• Polymorphism, the ability of a solid material to exist in multiple crystalline forms, is a critical factor in pharmaceutical development.
• Understanding the impact of different polymorphic forms on drug solubility and dissolution is essential for predicting bioavailability and therapeutic efficacy.

Purpose of the Study:

• To quantify the impact of drug polymorphism on solubility by analyzing existing literature data.
• To investigate trends in solubility ratios between different polymorphs and between anhydrate and hydrate forms.
• To explore the correlation between thermal data and solubility ratios for polymorphic systems.

Main Methods:

• Comprehensive literature review of studies reporting solubility or dissolution data for drug polymorphs.
• Statistical analysis of collected data to determine trends in solubility ratios.
• Estimation of solubility ratios using thermal data (e.g., melting points, enthalpies) as a predictive method.

Main Results:

• The general trend indicates that the solubility ratio between different polymorphs is typically less than 2.
• Solubility ratios for anhydrate/hydrate forms were observed to be more varied and generally higher than those for nonsolvated polymorphs.
• Estimated solubility ratios derived from thermal data showed good agreement with experimentally determined solubility values.

Conclusions:

• Drug polymorphism generally has a moderate impact on solubility, with ratios usually below 2.
• Anhydrate/hydrate systems exhibit greater variability in solubility ratios compared to nonsolvated polymorphs.
• Thermal analysis can serve as a useful predictive tool for estimating solubility differences between drug polymorphs.