Polymer-mediated drug supersaturation - A spotlight on the interplay between phase-separated amorphous drug colloids and dissolved molecules.

Colloidal aggregation phenomena have been found responsible for the supersaturation of poorly water-soluble drugs, potentially leading to bioavailability enhancements. Unlike coarse precipitates, phase separation in the form of colloids, is expected to enhance drug supersaturation performance. Therefore, a high proportion of these colloids should correlate with the extent and the kinetics of supersaturation. The prime objective of the current study is to provide a mechanistic understanding on supersaturation for the model drug albendazole (ALB) in combination with twelve polymers. Species separated after a pH-shift were characterized by dynamic light scattering (DLS), freeze-fracture electron microscopy (FF-EM) and transmission X-ray diffraction (XRD). Laser diffraction (LD) in a liquid cell was introduced for a relative quantification of the colloidally separated species, described as colloid fraction. The pH-dependent supersaturation was assessed online using a miniaturized dissolution assay. Here, a measure of the extent of amorphous colloidal phase separation was established, and its impact on supersaturation was evaluated. As a result, a correlation was found between the extent of supersaturation and the colloid fraction. This confirmed the dependence of polymer-mediated enabling and preservation of supersaturation on the ability of polymers to stabilize colloid fractions. Furthermore, a fixed ratio was suggested between the dissolved drug and colloidally separated drug as the kinetic profiles of both species showed similar trajectories. In conclusion, colloid fractions were identified to be responsible for dissolved and potentially bioavailable drug molecules.

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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.