Relationship Between Phase Solubility Diagrams and Crystalline Structures During Dissolution of...

Area of Science:

• Pharmaceutical Sciences
• Materials Science
• Crystallography

Background:

• Cyclodextrins (CDs) are widely used to improve drug physicochemical properties through complex formation.
• Limited studies have explored the direct correlation between the crystal structures of drug/CD complexes and their dissolution behavior.

Purpose of the Study:

• To develop cimetidine (CIM)/CD complex crystals for sustained drug release.
• To investigate the relationship between the crystal structures of CIM/CD complexes and their dissolution characteristics.

Main Methods:

• Formation of CIM/CD complex crystals using solvent mixing with three types of CDs (α-, β-, and γ-CD).
• Analysis of phase solubility diagrams to determine interaction profiles.
• Characterization of crystal structures (cage-type and channel-type).
• Measurement of dissolution rates and calculation of dissolution rate constants (k).

Main Results:

• CIM/CD complexes exhibited significantly reduced dissolution rates compared to physical mixtures.
• β-CD enhanced CIM solubility, while γ-CD decreased it, forming low-solubility complexes.
• CIM/α-CD formed cage-type crystals; CIM/β-CD and CIM/γ-CD formed channel-type crystals.
• Dissolution rate constants (k) for CIM/α-CD and CIM/β-CD were 0.045 h⁻¹ and 0.04 h⁻¹, respectively.
• Channel-type crystals of CIM/γ-CD were stabilized by water molecules.

Conclusions:

• The crystal structure of CIM/CD complexes critically influences dissolution behavior, enabling control over drug release rates.
• Different CD types (α-, β-, γ-) lead to distinct crystal architectures (cage vs. channel) and solubility profiles.
• Understanding these structure-dissolution relationships is key for designing advanced drug delivery systems.