Thermal behaviour, compatibility study and decomposition kinetics of glimepiride under isothermal and non-isothermal conditions

In the present work, the thermal decomposition of glimepiride (sulfonylurea hypoglycemic agent) was studied using differential scanning calorimetry (DSC) and thermogravimetry/derivative thermogravimetry (TG/DTG). Isothermal and non-isothermal methods were employed to determine kinetic data of decomposition process. The physical chemical properties and compatibilities of several commonly used pharmaceutical excipients (glycolate starch, microcrystalline cellulose, stearate, lactose and Plasdone(R)) with glimepiride were evaluated using thermoanalytical methods. The 1:1 physical mixtures of these excipients with glimepiride showed physical interaction of the drug with Mg stearate, lactose and Plasdone(R). On the other hand, IR results did not evidence any chemical modifications. From isothermal experiments, activation energy (E-a) can be obtained from slope of lnt vs. 1/T at a constant conversion level. The average value of this energy was 123 kJ mol(-1). For non-isothermal method E-a can be obtained from plot of logarithms of heating rates, as a function of inverse of temperature, resulting a value of 157 and 150 kJ mol(-1), respectively, in air and N-2 atmosphere, from the first stage of thermal decomposition.