Investigations on the polymorphism and pseudopolymorphism of triamcinolone diacetate

The glucocorticoide triamcinolone diacetate was investigated for polymorphism. Crystallization experiments in different solvents performed at room-temperature reveal that in most cases solvates has formed (form B) which are isotypic and which crystallize in the orthorhombic space group P212121. In their crystal structure channels are formed in which the solvent molecules are located. In some other solvents the commercial available form A is the thermodynamic most stable form. On heating form A using differential scanning calorimetry (DSC) the compound melts at a peak temperature of 136 °C without any further polymorphic transformation. If the solvents are removed at higher temperatures using simultaneous differential thermoanalysis and thermogravimetry coupled to mass spectroscopy (DTA–TG–MS) the remaining residues are amorphous against X-rays because the compound melts directly after desolvation. If the desolvation process is investigated by DSC measurements the same is observed for most solvents but in some cases different peaks for desolvation and melting are observed. In this case a new modification can be isolated after removing the solvent (form C). If the solvent are removed in vacuum or by storage at room-temperature always the commercial available form A is obtained, whereas desolvation experiments at 80 °C indicate the formation of a further polymorphic modification (form D).