Abstract
Four modifications (monohydrate, hemihydrate, anhydrate, and amorphous form) of oxyphenbutazone were prepared and characterized by the use of X-ray powder diffractometry, thermal analysis, infrared spectrophotometry, and elemental analysis. The physicochemical stability of the amorphous form was quantitatively investigated by X-ray diffractometry at three temperatures (25, 40, and 50°C) and three relative humidity levels (0, 50, and 75%). The amorphous form transformed to the anhydrate at low humidity, while it transformed to either the hemihydrate or the monohydrate at moderate or high humidity. These hydrates also converted to the anhydrate via the amorphous state at low humidity. The anhydrate did not transform under any storage conditions and showed the highest stability. Increase of temperature greatly acdelerated the transformation rate, but the transformation mechanism was not changed.Among the four modifications the dissolution properties of the hydrates were unexpectedly superior to those of the anhydrate or amorphous form.
