SPECTROSCOPIC CHARACTERIZATION OF INTERACTIONS BETWEEN PVP AND INDOMETHACIN IN AMORPHOUS MOLECULAR DISPERSIONS

Purpose. To study the molecular structure of indomethacin-PVP amorphou s solid dispersions and identify any specific interactions between the components using vibrational spectroscopy Methods. Solid dispersions of PVP and indomethacin were prepared using a solvent evaporation tech nique and IR and FT-Raman spectra were obtained. Results. A comparison of the carbonyl stretching region of gamma indomethacin, known to for m carboxylic acid dimers, with that of amorphous indomethacin indicate d that the amorphous phase exists predominantly as dimers. The hydroge n bonding of alpha indomethacin is not as dimers. Addition of PVP to a morphous indomethacin increased the intensity of the infrared band ass igned to non-hydrogen bonded carbonyl. Concomitantly, the PVP carbonyl stretch appeared at a lower wavenumber indicating hydrogen bonding. M odel solvent systems aided spectral interpretation. The magnitude of t he spectral changes were comparable for an indomethacin-PVP solid disp ersion and a solution of indomethacin in methylpyrrolidone at the same weight percent. Conclusions. Indomethacin interacts with PVP in solid dispersions through hydrogen bonds formed between the drug hydroxyl a nd polymer carbonyl resulting in disruption of indomethacin dimers. PV P may influence the crystallisation kinetics by preventing the self as sociation of indomethacin molecules. The similarity of results for sol id dispersions and solutions emphasises the ''solution'' nature of thi s binary amorphous state.