Hydrogen Bonding as a Failure Mechanism for Release of Ibuprofen-Copovidone Amorphous Solid Dispersions

Amorphous solid dispersions (ASDs) are often used to increase the bioavailability of poorly water-soluble drugs. However, there are substantial formulation challenges associated with optimizing their performance. The high polymer content needed to ensure rapid and extensive release creates a pill burden for patients, leading to lower compliance. To combat this problem, formulations with higher drug loading are desirable, but often have poor release. Previous research suggests that specific interactions between the drug and polymer can have a negative effect on ASD release, but the failure mechanisms are not fully understood. In this study, a model system of the low glass transition temperature drug, ibuprofen, and polyvinylpyrrolidone vinyl acetate (PVPVA) was used to investigate the mechanisms underlying poor release from an ASD with drug-polymer hydrogen bonding at high drug loading. Infrared spectroscopy was used to demonstrate the presence of hydrogen bonds between the carboxylic acid of ibuprofen and the pyrrolidone carbonyl group of PVPVA. ASD phase morphology following exposure to water, either via the vapor phase or following immersion in aqueous media, was studied using confocal fluorescence microscopy. Surface area normalized release studies of ASDs were performed at different drug loadings. Phase separation was readily induced following exposure to water vapor and was also observed following immersion in aqueous media. Furthermore, the resultant phase morphology varied with drug loading, changing from discrete drug-rich regions at low drug loading to continuous drug-rich regions at higher drug loading, explaining why release rate decreased dramatically with increasing drug load. Approximately 40% of PVPVA was present in the insoluble drug-rich phase, indicating a high affinity of the polymer for the drug in an aqueous environment, likely due to drug-polymer hydrogen bonding interactions. The presence of the polymer resulted in an increase in the volume of the insoluble drug-rich phase, underpinning the observed change in phase separation morphology at a relatively low drug loading. This study thus provides mechanistic understanding of the role played by drug-polymer hydrogen bonding in lowering the limit of congruency of PVPVA-based ASDs.