Co-relationship of physical stability of amorphous dispersions with enthalpy relaxation

Physical stability studies of valdecoxib (VLB) and its solid dispersions with PVP (1, 2, 5, 10, 15 and 20% w/w) were carried out by Differential Scanning Calorimetry (DSC). Change in specific heat with time was measured to determine the degree of crystallinity of amorphous drug and its binary dispersions after storage at 40 degrees C and 75% RH. The rate of crystallization was found to decrease with increasing PVP concentration and time for 10% crystallization (t(90%)) was found to increase significantly for the amorphous drug when formulated as PVP dispersions. Enthalpy relaxation was found to be inversely correlated with t(90%) (min) values and was found to be a good predictor of devitrification tendency and hence stability of amorphous VLB.