Aggregation behaviour of amphiphilic drug and bile salt mixtures at different compositions and temperatures

•Aggregation behavior of promethazine hydrochloride-bile salt mixtures has been investigated.•The negative β values indicate attractive interactions between the components.•For PMT/PMT-bile salt systems, ΔHm∘ values change from negative to positive with temperature.•The ΔSm∘ values are positive, their magnitude being more at T = 298.15 K and above.•The results have applicability in drug delivery.

The micellization and adsorption behaviour of the amphiphilic drug promethazine hydrochloride (PMT – a phenothiazine) and bile salts mixtures were analyzed at different compositions in pure and mixed states in aqueous solutions. By using regular solution theory (RST) and Rosen’s model different physicochemical properties such as critical micellar concentration (cmc), micellar composition, surface excess concentration (Γmax), minimum area per molecule (Amin), interaction parameters (βm, βσ), energetic parameters of micellization as well as other micellar and surface properties have been determined. The values of interaction parameters (β) and activity coefficients f1 and f2 (for both, in mixed monolayer as well as in mixed micelles) indicate the synergistic behaviour. The thermodynamic parameters propose release of water from the hydrophobic portion of the drug at higher temperatures.