How changes in molecular weight and PDI of a polymer in amorphous solid dispersions impact dissolution performance

Polymers functionally contribute to supersaturation and precipitation inhibition of the active pharmaceutical ingredient (API) in amorphous solid dispersions (ASD). Therefore, it is necessary to monitor physicochemical changes of the polymeric carrier caused by the manufacturing process. This is especially important when the material is exposed to heat and shear stress as in case of hot-melt extrusion (HME). This study evaluated the impact of HME process conditions on physical characteristics of poly(vinylpyrrolidone-co-vinyl-acetate) 60:40 (PVP-VA64) which is a widely used polymer for HME. Focus was set on molecular weight (M_w) and polydispersity index (PDI), by means of absolute molar mass detection via multi-angle light scattering. The generation of a high M_w fraction together with a decrease of the average M_w was detected. In a next step, the influence of these changes on the dissolution behavior of ASD was evaluated. Different stress conditions were applied onto PVP-VA64 in placebo extrusions. The obtained stressed polymer samples were subsequently used to prepare verum ASD with ketoconazole by spray drying (SD). SD dispersions (SDD) of thermally stressed PVP-VA64 were compared to SDD prepared with bulk powder. Although there were only slight changes in M_w and PDI, they significantly impacted supersaturation and precipitation of the formulation.