Abstract
Amorphous solid dispersions provide an excellent way of increasing dissolution rates of poorly soluble drugs, but there may be concerns about stability. One way of assessing the stability of amorphous materials is the study of relaxation. In this study the relaxation at the surface of amorphous solid dispersions (SDs) was evaluated using inverse gas chromatography (iGC). A SD containing 70% indomethacin and 30 % PVP K30 was prepared by melt quenching. The SD was put into the iGC and heated to 17℃ below Tg for aging, during which decane was injected repeatedly. The retention volume of decane decreased with aging time, indicating that the sample relaxed on the surface during aging. During this period of storage no crystallization was observed by PXRD or DSC. Therefore, it is obvious that the change in this retention volume is due to the structural relaxation of the amorphous solid dispersion. The data of retention volume showed a good fit on a Kohlraush-Williams-Watts (KWW) equation and the indicator of the structural relaxation, τ, was estimated. This value was much lower than that of bulk relaxation estimated by DSC. Therefore, it can be concluded that the structural relaxation at the surface happens faster than that of the bulk.
https://ror.org/027y26122 
