When slightly soluble drugs were dissolved or suspended in O/W type ointments, some drugs were crystallized or grew up in these preparations during storage for several months. In these cases, the efficacy and physical properties of these ointments were decayed. Therefore, the method to foretell the possibility of crystallization in various ointments in short time were investigated. Dequalinium chloride was used as a test drug and dissolved in the model preparations as 0.3% concentration. These preparations were stored at room temperature, constant temperatures of 5, 25, and 40°C and cyclizing temperatures from 5 to 25°C or 5 to 40°C everyday. The crystallization of the test drug in these preparations stored at various temperatures was observed by a polarizing microscope. After being stored at room temperature for six months, the crystallization of the test drug was slightly recognized, while, in the drug stored at constant temperatures of 20 and 40°C, the crystallization was not recognized. After a week, in the drug stored at 5°C and cyclizing temperature, the crystallization was recognized, and the crystals in these preparations stored at cyclizing temperature were bigger than those stored at 5°C.
