Solid-state investigation of fluocinolone acetonide

Three crystalline modifications of fluocinolone acetonide, A, B and C, were characterized by means of FTIR, DSC, TG-FTIR, MICRO-FTIR and X-ray diffractometry. They were easily differentiated by their IR absorption bands in the 3600-3400 cm-1 range. The thermal behavior was also elucidated using combined techniques; thermomicroscopy and thermogravimetry coupled with Fourier transform infrared spectroscopy were found to be very useful tools for a better understanding of thermal events. On heating, form A and C were fully converted into form B. Polymorph A was found to be enantiotropically related to B, while form C was monotropically related to B. The existence of three polymorphs was confirmed by means of their different X-ray diffraction patterns. Detailed methods of preparation of the three modifications are also described.