Amorphous solid dispersions (ASDs) of crystallizable drugs and polymer excipients are attractive for enhancing the solubility and bioavailability of hydrophobic drug molecules. In this study, the solution behavior of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (PND) and poly(vinylpyrrolidone-co-vinylacetate) (PVPVA), as polymer excipients, and nilutamide (NLT), phenytoin (PHY), and itraconazole (ITN) as model drugs, were monitored by an in vitro dissolution assay, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and polarized optical microscopy (POM). High degrees of drug supersaturation were coincident with the formation of amorphous nanoparticles in each system. The difference in particle size and kinetic stability between PND and PVPVA systems suggest a difference in how the polymers interact with the drug-rich phase. A series of scenarios are proposed based on whether the polymer interacts more strongly with the drug-rich nanoparticles or with water. Understanding the contribution of drug-rich nanoparticles to achievable supersaturation and the effect of polymer excipients on these particles will inform the design of future solid dispersion systems through a better understanding of the polymer/drug solution relationship.
Keywords: amorphous solid dispersions; drug delivery; drug-rich nanoparticles; polymer-drug interactions; solution-state.