Study of the pseudo-crystalline transformation from form i to form II of thiamine hydrochloride (vitamin B(1)).

The purpose of the current study was to evaluate the rate of the pseudo-crystalline transformation of thiamine hydrochloride form I to form II depending on the temperature and humidity. Changes in the appearance and weight of form I crystals were observed under humidified conditions using a water vapor sorption system equipped with a CCD camera. The form I crystals and tablets were stored under various temperature and humidity conditions (the saturation salt desiccator method), and the pseudo-crystalline transformation was observed using X-ray powder diffractometry with our laboratory equipment for drug substances and using synchrotron X-ray powder diffractometry for tablets. It was confirmed that the activation energy in the pseudo-crystalline transformation rate from form I to form II was dependent on humidity, and the calculated values were 121-155 kJ/mol at 70-90% relative humidity. Moreover, when thiamine hydrochloride was formulated as tablets, it was confirmed that the transformation rate was slower compared with the drug substances alone. The pseudo-crystalline transformation rate therefore declined after formulation in tablet form, perhaps due to the shielding effects of thiamine hydrochloride crystal from contact with water molecules by excipients, compaction, etc.