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Addressing the Accuracy of Plasma Protein Binding Measurement for Highly Bound Compounds Using the Dilution Method

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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.

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Fig. 1
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Data Availability

All data generated or analysed during this study are included in this published article.

Abbreviations

ACN:

Acetonitrile

DDI:

Drug-drug interaction

f u :

Fraction unbound

f u , d :

Diluted fraction unbound

HPLC:

High-performance liquid chromatography

LC–MS/MS:

Liquid chromatography with tandem mass spectrometry

MRM:

Multiple reaction monitoring

PBS:

Phosphate-buffered saline

PPB:

Plasma protein binding

PK:

Pharmacokinetics

PK/PD:

Pharmacokinetics/pharmacodynamics

TI:

Therapeutic index

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Acknowledgements

The authors greatly appreciate the help of Sophia M. Shi in editing the manuscript.

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Authors and Affiliations

  1. Pharmacokinetics, Dynamics and Metabolism, Pfizer Worldwide Research and Development, 445 Eastern Point Road, Groton, Connecticut, USA

    Sangwoo Ryu & Li Di

  2. Modeling and Simulation, Pfizer Worldwide Research and Development, Cambridge, Massachusetts, USA

    David Tess

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  1. Sangwoo Ryu
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Contributions

Sangwoo Ryu, David Tess and Li Di all contributed to the following areas: substantial contributions to the conception or design of the work; or the acquisition, analysis, or interpretation of data for the work; and drafting the work or revising it critically for important intellectual content; and final approval of the version to be published; and agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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Correspondence to Li Di.

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Ryu, S., Tess, D. & Di, L. Addressing the Accuracy of Plasma Protein Binding Measurement for Highly Bound Compounds Using the Dilution Method. AAPS J 25, 7 (2023). https://doi.org/10.1208/s12248-022-00774-2

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