水通常容易被无定形化合物吸收,降低其玻璃化转变温度(Tg)并促进其重结晶(通过成核和生长)。同时,水分含量的增加转化为热力学溶解度和固有溶解速率的降低,与相应的干燥(纯)非晶相相比,例如,见[MurdandeSB,PikalMJ,ShankerRM,BognerRH.2010.无定形药物的溶解度优势:I.热力学分析。JPharmSci99:1254-1264。].在纯吲哚美辛和非洛地平的情况下,每个非晶相相对于其结晶对应物的溶解度优势先前分别确定为7.6和4.7,使用一种新的方法以及从文献中获取的基本量热数据。在这里,我们证明,理论上,在吸收了0.5%w/w的水之后,溶解度比以相同的顺序降低到6.9和4.5。此外,由于预测的固有溶解速率(基于Noyes-Whitney方程)与给定的无定形晶体对的溶解度优势成正比,它随着水分的吸收成比例地减少。应用本文提出的方法,可以直接预测在任何水分含量下观察到的Tg降低的程度,对于给定的非晶相。知道这个价值,与纯玻璃相比,可以估计增塑相的溶解度和/或固有溶解速率的相对降低,反之亦然。
Water is often readily absorbed by amorphous compounds, lowering their glass transition temperature (Tg) and facilitating their recrystallization (via nucleation-and-growth). At the same time, the increase in moisture content translates to a decrease in both the thermodynamic solubility and intrinsic dissolution rate, as compared to the corresponding dry (pure) amorphous phase, e.g. see [Murdande SB, Pikal MJ, Shanker RM, Bogner RH. 2010. Solubility advantage of amorphous pharmaceuticals: I. A thermodynamic analysis. J Pharm Sci 99:1254-1264.]. In the
case of pure indomethacin and
felodipine, the solubility advantage of each amorphous phase over its crystalline counterpart were previously determined to be 7.6 and 4.7, respectively, using a new methodology together with basic calorimetric data taken from the literature. Herein, we demonstrate that, theoretically, following the uptake of just ∼0.5% w/w water, the solubility ratios decrease to 6.9 and 4.5, in the same order. Moreover, as the predicted intrinsic dissolution rate (based on the Noyes-Whitney equation) is directly proportional to the solubility advantage of a given amorphous-crystalline pair, it decreases proportionately upon moisture uptake. Applying the methodology presented herein, one can directly predict the extent of Tg-lowering observed at any moisture content, for a given amorphous phase. Knowing that value, it is possible to estimate the relative decrease in the solubility and/or intrinsic dissolution rate of the plasticized phase compared to the pure glass, and vice-versa.