Rapid insight into heating-induced phase transformations in the solid state of the calcium salt of atorvastatin using multivariate data analysis.

PURPOSE

To investigate the heating-induced dehydration and melting behavior of the trihydrate phase of the calcium salt of atorvastatin.

METHODS

Multivariate curve resolution (MCR) was used to decompose a variable-temperature synchrotron X-ray powder diffraction (VT-XRPD) data matrix into diffraction patterns and concentration profiles of pure drug phases.

RESULTS

By means of the MCR-estimated diffraction patterns and concentration profiles, the trihydrate phase of the drug salt was found to dehydrate sequentially into two partially dehydrated hydrate structures upon heating from 25 to 110°C, with no associated breakage of the original crystal lattice. During heating from 110 to 140°C, the remaining water was lost from the solid drug salt, which instantly collapsed into a liquid crystalline phase. An isotropic melt was formed above 155°C. Thermogravimetric analysis, hot-stage polarized light microscopy, and hot-stage Raman spectroscopy combined with principal component analysis (PCA) was shown to provide consistent results.

CONCLUSIONS

This study demonstrates that MCR combined with VT-XRPD is a powerful tool for rapid interpretation of complex dehydration behavior of drug hydrates, and it is also the first report on a liquid crystalline phase of the calcium salt of atorvastatin.