Glass transition study of eutectic mixtures for pharmaceutical applications

Several blends of PEG 6000 - SR 33557 (those with a glass transition detect ed on cooling: 20-30 wt% PEG 6000) were heated at different heating rates, beta. Solidification depends on both the cooling rate (alpha) and the mixtu re composition. A glass transition was detected by differential scanning ca lorimetry (DSC) in mixtures containing drug (SR 33557) > 60 wt%. The depend ence of the glass transition temperature, T-g, on the heating rate is analy zed using an empirical relationship of the kind T-g = A + B In beta and the activation energy concept. The parameter B is nearly a constant, 1.7 +/- 0 .2 blends with drug content > 60 wt%. Activation energies obtained were 370 +/- 35 kJ/mol for the drug and 250 +/- 20 kJ/mol for the mixture with 20 w t% excipient. Moreover, the effect on T-g of cooling rate is analyzed. In s amples cooled at different rates and heated at the same rate, the glass tra nsition temperature increases as previous cooling rate increases. (C) 2001 Elsevier Science B.V. All rights reserved.