Towards a better understanding of solid dispersions in aqueous environment by a fluorescence quenching approach

Solid dispersions (SDs) represent an important formulation technique to achieve supersaturation in gastro-intestinal fluids and to enhance absorption of poorly water-soluble drugs. Extensive research was leading to a rather good understanding of SDs in the dry state, whereas the complex interactions in aqueous medium are still challenging to analyze. This paper introduces a fluorescence quenching approach together with size-exclusion chromatography to study drug and polymer interactions that emerge from SDs release testing in aqueous colloidal phase. Celecoxib was used as a model drug as it is poorly water-soluble and also exhibits native fluorescence so that quenching experiments were enabled. Different pharmaceutical polymers were evaluated by the (modified) Stern-Volmer model, which was complemented by further bulk analytics. Drug accessibility by the quencher and its affinity to celecoxib were studied in physical mixtures as well as with in SDs. The obtained differences enabled important molecular insights into the different formulations. Knowledge of relevant drug-polymer interactions and the amount of drug embedded into polymer aggregates in the aqueous phase is of high relevance for understanding of SD performance. The novel fluorescence quenching approach is highly promising for future research and it can provide guidance in early formulation development of native fluorescent compounds.