Measurement of surface glass transition temperature of amorphous cefditoren pivoxil granules by inverse gas chromatography

The aim of the present study is to increase the knowledge about the molecular mobility of cefditoren pivoxil (CDTR-PI) on the granules surface by studying the glass transition temperature (Tg) of the drug using inverse gas chromatography (IGC), and to clarify the inhomogeneity of the granule resulting in the physical stability of them. The Tg of the granulated amorphous CDTR-PI and the granulated CDTR-PI with polymers were measured by inverse gas chromatography (IGC) and differential scanning calorimetry (DSC). There was no difference among samples in the Tg measured by DSC. However, the Tg measured by IGC were different among samples; the value of CDTR-PI with hydroxypropylcellulose (HPC-L) was lower than the others, and showed a tendency similar to spray-dried samples. It was suggested that IGC measured the surface transition temperatures of granules that was impossible to measure by DSC. By comparison with the influence of the Tg on the surface and the whole granule on the crystallization rates of them, the surface Tg strongly affected the physicochemical stability of granules compared to those of the whole.