Influence of relative humidity on the interaction between different aryl propionic acid derivatives and poly(vinylpyrrolydone) K30: evaluation of the effect on drug bioavailability.

The present work assessed the physical interactions between several aryl propionic acid derivatives and polyvinyl(pyrrolidone) K30 (PVP), stored together at 298+/-0.5K at different relative humidities (RH 55, 75 and 86%). Results were compared to those obtained at low RH (22%), published in a previous paper. The water uptake percentage of binary mixtures were intermediate between that of pure PVP and pure drugs. By X-ray powder diffraction, for all the drugs, it was possible to note a marked decrease in crystallinity degree, in particular at highest RH%. The loss in crystallinity degree may be considered an evidence of the physicochemical interaction between the polymer and the drug, supporting the formation of a solid dispersion. By high-resolution (1)H solid-state NMR spectrometry, it was possible to observe an increase of drug-polymer interaction with aging, with the only exception of ibuprofen. Molecular docking proved the establishment of Van der Waals and electrostatic interactions for all the mixtures, and for mixtures with fenbufen and naproxen, also hydrogen bonds. The application of Gordon-Taylor rule to the thermal analysis revealed that the requirement of volume additivity of this rule was not fulfilled for any mixture, and a negative deviation from theoretical behaviour was always observed. The hydration of drug-PVP mixtures had important repercussion on drug solubility and intrinsic dissolution rate (IDR). In general, an increase in water solubility and consequently an increase in IDR were observed, with few exceptions, at highest RH%.