Polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG) solid dispersion systems with flavanone glycosides, naringin and hesperidin, and their aglycones, naringenin and hesperetin, were prepared, using solvent evaporation method, to enhance their dissolution rates that may affect their bioavailability. Drug release of both flavanone glycosides and their aglycones was directly affected by the physical state of solid dispersions. Powder-XRD technique in combination with scanning and transmission electron microscopy revealed that PVP polymer formed amorphous nanodispersion systems with flavanone aglycones, while such systems could not be formed with their glycosides, which are bulkier molecules. Fourier transform infrared spectra suggest the presence of hydrogen bonds between PVP carbonyl groups and hydroxyl groups of both flavanone aglycones. These interactions prevent the crystallization of naringenin and hesperetin aglycones in PVP matrix. On the other hand, the ability of PEG carrier to form hydrogen bonds with flavanone glycosides or aglycones was limited, and as a result both flavanone glycosides and their aglycones remain in the crystalline form. For this reason, the solubility enhancement of PEG solid dispersions was lower than when PVP was used as drug carrier. At pH 6.8, the % release of naringenin and hesperetin from PVP/naringenin–hesperetin (80/20 w/w) solid dispersion was 100% while in PEG solid dispersions, it was not higher than 60–70%. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 460–471, 2006
Polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG) solid dispersions with Felodipine or Hesperetin having up to 20 wt% drug were prepared using solvent evaporation method. Solid dispersions in comparison with their physical mixtures were studied using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and hot stage polarizing light microscopy (HSM). PVP formulations with low drug load proved to be amorphous, since no crystalline Felodipine or Hesperetin drugs were detected using DSC and WAXD. Low and fast heating rates were applied for DSC study, to prevent changes in the samples caused during heating. Similarity between results of WAXD and DSC was also found in the case of physical mixtures, where the drug was in the crystalline state. However, though specific tests showed the high sensitivity of the DSC technique, it was difficult to arrive to reliable results for PEG solid dispersions or physical mixtures with low drug content by DSC, even by high heating rates. Crystalline drug could not be detected by DSC, leading to erroneous conclusions about the physical state of the drug, in contrast to WAXD. On the other hand, HSM proved the presence of small drug particles in the solid dispersions with PEG and the dissolution of the drug in the melt of PEG on heating. In such systems, in which a polymer with low melting point is used as drug carrier, DSC is inappropriate technique and must be used always in combination with HSM. The coupling of WAXD with thermal analysis, allowed complete physicochemical characterization and better understanding which is essential for a first prediction of dissolution characteristics of such formulations.