Exploration of solubilisation effects facilitated by the combination of Soluplus® with ionic surfactants

Preclinical testing of new drug candidates frequently necessitates high-dose solution formulations to support robust testing in rodent models. This study aimed to expand the range of high solubilisation capacity formulations by exploring the solubilisation effects of the polymeric surfactant Soluplus® in combination with ionic surfactants. The interactions between Soluplus® and three ionic surfactants, sodium dodecyl sulphate, dioctyl sodium succinate, and sodium oleate, with a primary focus on solubility enhancement were investigated over a range of ionic surfactant concentrations. The solubilisation profiles for seven model drugs were obtained, and the vehicles were characterised by their visual characteristics, dynamic light scattering, and viscosity measurements. The solubilisation profiles were non-linear, indicating the formation of different colloidal species with individual solubilisation strengths depending on surfactant type and concentration, demonstrating substantial solubility enhancement. For certain drugs more than additive solubilisation, facilitated by synergistic interactions between Soluplus® and the ionic surfactants, was obtained. Overall, the solubility increase provided by the excipient combinations resulted in non-linear and drug specific solubilisation profiles. The non-linearities observed were reflected in visual observations of the vehicles appearance, DLS and viscosity measurements, which collectively indicated a change in polymer aggregation with increasing concentration of anionic surfactant. This investigation highlights that already low quantities of ionic surfactants introduced to Soluplus® may substantially enhance solubility, which offers a promising approach for further exploration in preclinical drug development where more conventional solubilising formulation strategies may fall short.