Thermal Study of Anhydrous and Hydrated Forms of Olanzapine

Anhydrous and hydrated forms of olanzapine were obtained by crystallization using different experimental pathways and analysed by differential scanning calorimetry and thermogravimetric techniques. The unsolvated form I could be prepared by direct crystallization from a limited number of solvents; the form II could obtained only after desolvation of selected solvates. At thermal analysis the form I and II of olanzapine demonstrated to be polymorphs; while the form III appears to be rather a solvate of undefined stoichiometry. The hydrated forms were obtained both from fully and partially aqueous media, and only with difficulty by direct crystallization from water, due to very poorly solubility in water of the drug. Depending on the experimental conditions, hydrates of different composition could be obtained that, on de-hydration, leave the de-hydrated forms of olanzapine, possibly via-(partial) amorphization.