Modelling of cetylpyridinium chloride availability in complex mixtures for the prediction of anti-microbial activity using diffusion ordered spectroscopy, saturation transfer difference and 1D NMR

Background/Objectives: A range of NMR techniques, including diffusion ordered spectroscopy (DOSY) were used to characterise complex micelles formed by the anti-microbial cationic surfactant cetylpyridium chloride and to quantify the degree of interaction between cetylpyridium chloride and hydroxyethyl cellulose in a variety of commercially relevant formulations as a model for the disk retention assay. Methods: This NMR-derived binding information was then compared with the results of formulation analysis by traditional disk retention assay (DRA) and anti-microbial activity assays to assess the suitability of these NMR techniques for the rapid identification of formulation components that could augment or retard antimicrobial activity DRA. Results: NMR showed a strong ability to predict anti-microbial activity for a diverse range of formulations containing cetylpyridinium chloride (CPC). Conclusions: This demonstrates the value of this NMR-based approach as a rapid, relatively non-destructive method for screening commercial experimental anti-microbial formulations for efficacy and further helps to understand the interplay of excipients and active ingredients.