The impact of applying an additional polymer coating on high drug-loaded amorphous solid dispersions layered onto pellets.

Inhibiting surface crystallization is an interesting strategy to enhance the physical stability of amorphous solid dispersions (ASDs), still preserving high drug loads. The aim of this study was to investigate the potential surface crystallization inhibitory effect of an additional polymer coating onto ASDs, comprising high drug loads of a fast crystallizing drug, layered onto pellets. For this purpose, bilayer coated pellets were generated with fluid-bed coating, of which the first layer constitutes a solid dispersion of naproxen (NAP) in poly(vinylpyrrolidone-co-vinyl acetate) (PVP-VA) in a 40:60 or 35:65 (w/w) ratio, and ethyl cellulose (EC) composes the second layer. The physical stability of these double-layered pellets, in comparison to pellets with an ASD layer only, was assessed under accelerated conditions by monitoring with X-ray powder diffraction (XRPD) at regular time intervals. Bilayer coated pellets were however found to be physically less stable than pellets with an ASD layer only. Applying the supplementary EC coating layer induced crystallization and heterogeneity in the 40:60 and 35:65 (w/w) NAP-PVP-VA ASDs, respectively, attributed to the initial contact with the solvent. Caution is thus required when applying an additional coating layer on top of an ASD layer with fluid-bed coating, for instance for controlled release purposes, especially if the ASD consists of high loads of a fast crystallizing drug.