Department of Pharmaceutical Chemistry, Semmelweis University, H-1092 Budapest, Hőgyes Endre u. 9, Hungary.
Department of Pharmaceutical Chemistry, Semmelweis University, H-1092 Budapest, Hőgyes Endre u. 9, Hungary.
Eur J Pharm Sci. 2017 Aug 30;106:133-141. doi: 10.1016/j.ejps.2017.05.064. Epub 2017 May 31.
Incubation time plays a critical role in the accurate measurement of equilibrium solubility of compounds. Substances which dissolve very slowly generally need long incubation times (days or weeks) to reach equilibrium. However, long times may pose several problems, such as decomposition of solute, molding of buffer, and drifting of pH. Higuchi in 1979 proposed the Facilitated Dissolution Method (FDM) to dramatically reduce incubation time. It employs a small volume of water-immiscible organic solvent to partly solubilize the sample and thereby increase the surface area available for dissolution. The method has been used only rarely. In this study we performed a systematic validation of FDM using progesterone as model compound. The reference solubility value, 7.95±0.21μg/mL (p<0.05, n=5), was determined in Britton-Robinson buffer solution (pH7.4) at 25.0°C by the standardized protocol of Saturation Shake-Flask (SSF) method. Also, the solubility was measured by the FDM approach under varied experimental conditions (e.g., type and volume of organic solvent, time of agitation, and amount of solid excess), and compared to the reference value. It was demonstrated that the small amount of organic solvent used in the FDM does not impact the measured solubility, compared to the reference value. Additionally, four compounds of low dissolution rate (dexamethasone, digoxin, haloperidol and cosalane) were used to demonstrate that FDM can reduce the long equilibration time to the standardized 24h (6h stirring and 18h sedimentation). The time dependence of solubility equilibrium was measured by SSF, and the results were compared with those obtained by FDM. Our study, based on >200 solubility experiments, supports the validity of Higuchi's method. In this study we propose a standardized protocol for the FDM, where 1% v/v of organic solvent is used. Octane (or isooctane) was found to be suitable for highly hydrophobic compounds. Alternatively, octanol or 1,2-dichloroethane can be used for less lipophilic compounds.
孵育时间在准确测量化合物的平衡溶解度方面起着关键作用。溶解非常缓慢的物质通常需要较长的孵育时间（数天或数周）才能达到平衡。然而，长时间可能会带来一些问题，例如溶质分解、缓冲液固化和 pH 值漂移。Higuchi 在 1979 年提出了促进溶解法（FDM）来显著缩短孵育时间。它使用少量的与水不混溶的有机溶剂部分溶解样品，从而增加可用溶解表面积。该方法很少被使用。在这项研究中，我们使用孕酮作为模型化合物对 FDM 进行了系统验证。参考溶解度值 7.95±0.21μg/mL（p<0.05，n=5）是在 25.0°C 下用 Britton-Robinson 缓冲溶液（pH7.4）通过饱和摇瓶（SSF）方法的标准化方案确定的。此外，还根据不同的实验条件（例如，有机溶剂的类型和体积、搅拌时间和过量固体的量）通过 FDM 方法测量溶解度，并与参考值进行比较。结果表明，与参考值相比，FDM 中使用的少量有机溶剂不会影响测量的溶解度。此外，还使用四种低溶解速率的化合物（地塞米松、毛地黄毒苷、氟哌啶醇和考沙兰）来证明 FDM 可以将长平衡时间缩短至标准化的 24 小时（6 小时搅拌和 18 小时沉淀）。通过 SSF 测量溶解度平衡的时间依赖性，并将结果与 FDM 获得的结果进行比较。我们的研究基于>200 个溶解度实验，支持 Higuchi 方法的有效性。在这项研究中，我们提出了 FDM 的标准化方案，其中使用 1%v/v 的有机溶剂。己烷（或异辛烷）适用于高度疏水性化合物。或者，可以使用辛醇或 1,2-二氯乙烷来处理疏水性较低的化合物。
