Effect of hydrogen bonding interactions on the release mechanism of felodipine from nanodispersions with polyvinylpyrrolidone.

Solid dispersion systems are widely investigated for the dissolution enhancement of poorly water soluble drugs. Nevertheless, very limited commercial use has been achieved due to the poor predictability of such systems caused by the lack of a basic understanding of the dissolution optimization mechanism. In the present study an investigation of the release mechanism is performed for solid dispersion systems composed by polyvinylpyrrolidone (PVP) and felodipine (FEL), based on a correlation of their hydrophilicity with the intensity of interactions. The existing interactions were evaluated by using NMR and UV spectroscopy while molecular simulation techniques were also enabled. It was found that the interactions that take place correspond to the creation of hydrogen bonds. The correlation between the intensity of interactions and the concentration of PVP in the matrix showed a sigmoid function. The interactions are impressively increased for polymer concentration exceeding 75% (w/w). This phenomenon was well explained by using the molecular simulation technique. A similar sigmoid pattern was found for the function between dissolution profiles and polymer concentration in the matrix, indicating that the intensity of interactions promotes the dissolution enhancement. Investigation of the solubility and the particle size distribution of FEL in the binary system appeared to have similar behaviour indicating that the interactions affect the release profile through these two factors. The hydrophilicity of PVP does not significantly affect this enhancement as the contact angle was found to be linear to PVP concentration. Microscopic observation of the dissolution behaviour showed that FEL remains in fine dispersion in aqueous solution, verifying the release mechanism.