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, Tg, as a function of mixture composition and the nonisothermal and isothermal crystallization of the indomethacin. Values of Tg 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 Tg, whereas comparable inhibition with PVP was observed at storage temperatures 5 degrees C above Tg. This suggests that the inhibition of indomethacin crystallization by PVP may involve mechanisms other than just the general antiplasticizing effect (raising Tg) by PVP.