INHIBITION OF INDOMETHACIN CRYSTALLIZATION IN POLY(VINYLPYRROLIDONE) COPRECIPITATES

Differential scanning calorimetry and powder X-ray diffraction studies have been carried out with amorphous coprecipitates of indomethacin and poly(vinylpyrrolidone), PVP, to measure the glass transition temperature, T-g, as a function of mixture composition and the nonisothermal and isothermal crystallization of the indomethacin. Values of T-g as a function of mixture composition followed the ideal Gordon-Taylor equation up to about 50% w/w PVP. Inhibition of crystallization occurred at levels as low as 5% PVP and very significant inhibition was observed at and above 20% PVP. Inhibition of crystallization of indomethacin in the absence of PVP required a storage temperature 40-50 degrees C below T-g, whereas comparable inhibition with PVP was observed at storage temperatures 5 degrees C above T-g. This suggests that the inhibition of indomethacin crystallization by PVP may involve mechanisms other than just the general antiplasticizing effect (raising T-g) by PVP.