Characterization of the distribution, polymorphism, and stability of nimodipine in its solid dispersions in polyethylene glycol by micro-Raman spectroscopy and powder X-ray diffraction

In the present study, a series of solid dispersions of the drug nimodipine using polyethylene glycol as carrier were prepared following the hot-melt method. Micro-Raman spectroscopy in conjunction with X-ray powder diffractometry was used for the characterization of the solid structure, including spatial distribution, physical state, and presence of polymorphs, as well as storage stability of nimodipine in its solid formulations. The effect of storage time on drug stability was investigated by examination of the samples 6 months and 18 months after preparation. Confocal micro-Raman mapping performed on the samples showed that the drug was not uniformly distributed on a microscopic level. The presence of crystals of nimodipine with sizes varying between one and several micrometers was detected, and the crystal size seemed to increase with overall drug content. In samples examined 6 months after preparation it was found that the crystals existed mainly as the racemic compound, whereas after 18 months of storage mainly crystal conglomerates were observed.