Self-organizing Map Analysis for Understanding Comprehensive Relationships between Formulation Variables, State of Water, and the Physical Stability of Pharmaceutical Emulsions.

The physical stability of pharmaceutical emulsions is an important quality attribute to be considered. To obtain a better understanding of this issue, this study investigated the contribution of the state of water to the physical stability of pharmaceutical emulsions. The key technology to evaluate the state of water was magnetic resonance imaging (MRI). For sample preparation, model emulsions with different formulation variables (surfactant content, water content, and hydrophilic-lipophilic balance) were prepared. The T1 relaxation time, diffusion coefficient, and viscosity were measured as physical properties. The physical stability of the samples was evaluated using apparent diffusion coefficient maps acquired by MRI. Data analysis of the observed data was performed using the nonlinear response surface method and Kohonen's self-organizing map (SOM). It was determined that, depending on the formulation variables, the state of water was substantially changed and it played a significant role in the physical stability. SOM analysis successfully classified the conditions of formulation variables into four distinct clusters in terms of the similarity of the physical properties of the resultant emulsions, and then clarified the characteristics of the stable emulsions. This study provided us with a comprehensive understanding of the formulation variables, physical properties, and stability concerning the preparation of the model emulsion.