Abstract：
Currently, regulatory guidelines recommend using 0.01 as the lower limit of plasma fraction unbound (fu) for prediction of drug-drug interactions (DDI) to err on the conservative side. One way to increase experimental fu of highly bound compounds is to dilute the plasma. With the dilution method, a diluted fu, or fu,d, of ≥ 0.01 can be achieved by adjusting the dilution factor. The undiluted fu can be calculated from fu,d and be used for DDI prediction. In this study, the dilution method was evaluated, and the results showed that it gave similar fu values as those determined using the pre-saturation method without plasma dilution. The dilution method enables generation of accurate fu values and alignment with the regulatory recommendation of reportable fu values of ≥ 0.01 for DDI prediction. We recommend using the dilution method to bridge the regulatory recommended fu limit of 0.01 for DDI prediction and the pre-saturation or equivalent methods for definitive plasma protein binding studies. As the pharmaceutical industry continues to generate high quality PPB data, regulatory agencies will gain confidence in the accuracy of fu measurements for highly bound compounds, and the fu lower limit may no longer be needed in the future.
摘要：
目前,监管指南建议使用0.01作为血浆未结合分数（fu）的下限，以预测药物-药物相互作用（DDI）在保守方面的错误。增加高度结合化合物的实验fu的一种方法是稀释血浆。用稀释法,一个稀释的fu，或者fu，D,≥0.01可以通过调整稀释因子来实现。未稀释的fu可以从fu计算，d并用于DDI预测。在这项研究中,对稀释方法进行了评估，结果表明，它的fu值与不使用血浆稀释的预饱和法测定的值相似。稀释方法可以生成准确的fu值，并与DDI预测的可报告fu值≥0.01的监管建议保持一致。我们建议使用稀释方法来桥接DDI预测的监管建议的fu限值0.01，以及确定的血浆蛋白结合研究的预饱和或等效方法。随着制药行业不断产生高质量的PPB数据，监管机构将对高度结合化合物的fu测量的准确性充满信心，将来可能不再需要fu下限。
