Objectives To provide a comprehensive understanding of the competing thermodynamic and kinetic factors governing the crystallization of various hydrate systems. The ultimate goal is to utilize this understanding to improve the control over the unit operations involving hydrate formation, as well as to optimize the bioavailability of a given drug product. Key findings The thermodynamic and kinetic factors that govern hydrate crystallization are introduced and the current status of the endeavour to gain a mechanistic understanding of the phenomena that occur during the crystallization of different hydrate systems is discussed. The importance of hydrate investigation in the pharmaceutical field is exemplified by examining two specific hydrate systems: the polymorphic hydrate system and hydrates of pharmaceutical salts. Summary This review identifies the factors that are of critical importance in the investigation of anhydrate/hydrate systems. This knowledge can be used to control the phase transformation during pharmaceutical processing and storage, as well as in building a desired functionality for the final formulation.
Near-infrared spectroscopy was utilized as a polymorph
screening method. A model compound (sulfathiazole) was
recrystallized from various solvents, and the crystals were
milled using a planetary ball mill and compressed using
a hydraulic press. The polymorphism of recrystallized and
processed samples and the effect of processing on the
polymorphism of sulfathiazole was studied by near-infrared (NIR) spectroscopy and verified by X-ray powder
diffraction (XRPD) and thermal analysis. Polymorphism
and the degree of crystallinity of the processed samples
were studied, and NIR spectroscopy proved to be a fast
tool for polymorph screening and monitoring the processing-induced transformations. After clustering of the NIR
spectra of various samples, XRPD and complementary
methods can be applied to a more thorough analysis of
different clusters. This approach provides a timesaving
improvement for the polymorph analysis in the case of
large number of samples.
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