Stability of cyanocobalamin in sugar-coated tablets

The purpose of this study was to clarify the stability of cyanocobalamin (VB12-CN) in sugar-coated tablets containing fursultiamine hydrochloride (TTFD-HCl), riboflavin (VB2), and pyridoxine hydrochloride (VB6), and to identify the factors affecting the stability of VB12-CN in these sugar-coated tablets. The stability of VB12-CN was investigated using high-performance liquid chromatography while decomposition was evaluated kinetically. The decomposition of VB12-CN in sugar-coated tablets with high equilibrium relative humidity (more than 60%) under closed conditions showed complex kinetics and followed an Avrami–Erofe’ev equation, which expresses a random nucleation (two-dimensional growth of nuclei) model. We showed that equilibrium relative humidity, the incorporation of VB2 and VB6, and sugar coating, are the main factors influencing decomposition and that these factors cause the complex decomposition kinetics.