[Formulation Design and Evaluation Based on the Rheological Analysis]

The introduction of rheology-based indices into pharmaceutical formulation design and evaluation is expected to enable the establishment of a theoretical framework based on physical principles, offering an alternative to conventional optimization strategies that have relied on empirical techniques and rules. Properties such as structural attributes, disintegration behavior, and process responsiveness involve complex mechanical responses-including time-dependent deformation and structural relaxation-that cannot be sufficiently characterized by viscosity measurements under steady shear conditions. Evaluating not only viscosity but also dynamic viscoelasticity enables quantitative assessment of the functional roles of drugs and excipients within the formulation. This review outlines studies that have evaluated the physicochemical properties and functional performance of pharmaceutical formulations based on rheological measurements. It first summarizes research investigating how the viscoelastic properties of pharmaceutical excipients affect formulation characteristics, and then describes approaches for developing rheology-based indices that reflect the functional behavior of thixotropic spray formulations and disintegrants. Through the establishment of a framework based on physicochemical principles, the rheological approach has the potential to support the development of a new paradigm in formulation design-one that enables mechanism-based optimization and enhances reproducibility across various pharmaceutical dosage forms.