Characterization, quantification and stability of differently prepared amorphous forms of some oral hypoglycaemic...

The study deals with the investigation of possible differences induced in the physicochemical properties within the amorphous forms prepared by different methods. Enthalpy of solution measured by solution calorimetry was utilized to highlight the differences prevailing within the amorphous forms and to determine the percentage of amorphous content. Emphasis is laid on the quantification and physical stability of these forms. Amorphization was induced in poorly water-soluble oral hypoglycaemic agents (repaglinide, gliclazide and glipizide), by quench cooling, vaporization under reduced pressure and lyophilization. The amorphous nature was evident from a halo pattern in powder X-ray diffraction. A glass transition event is evident in differential scanning calorimetry thermograms of the amorphous forms of the three drugs. As expected, the amorphous forms show improvement in solubility and dissolution profiles. On subjecting these amorphous forms to different relative humidities at 25°C for three months and subsequent analysis showed that amorphous form of repaglinide prepared by quench cooling is most stable and has the potential to be formulated without any additive while amorphous form of gliclazide tends to devitrify pointing towards its unstable nature.