Prediction of polymorphic transformations of paracetamol in solid dispersions

A novel approach employing variable-temperature X-ray powder diffraction (VTXRPD) was used to exploit its suitability as an off-line predictive tool to study the polymorphic transformations of paracetamol (PMOL) in melt-extruded hydrophilic polymer matrices. Physical mixtures (PMs) and extruded formulations of PMOL with either polyvinyl caprolactam graft copolymer (Soluplus®) or vinylpyrrolidone–vinyl acetate copolymer (Kollidon®) in the solid state were characterized by using differential scanning calorimetry, hot-stage microscopy, and scanning electron microscopy. The experimental findings from VTXRPD showed that the stable Form I (monoclinic) of PMOL transformed to the metastable polymorph Form II (orthorhombic) at temperatures varying from 112°C to 120°C, in both the PMs and extrudates suggesting an effect of both temperature and identity of the polymers. The findings obtained from VTXRD analysis for both the PMs and the extruded formulations were confirmed by in-line near-infrared (NIR) monitoring during the extrusion processing. In the NIR study, PMOL underwent the same pattern of polymorphic transformations as those detected using VTXPRD. The results of this study suggest that VTXRPD can be used to predict the polymorphic transformation of drugs in polymer matrices during extrusion processing and provides a better understanding of extrusion processing parameters