Plasma Protein Binding & ICH M12: Assay Advances

Poster showcasing method validation and future work on plasma protein binding for highly bound compounds, with bar graph visuals.

Poster Authors:

Laura Tomlinson, Lerryn Hilton, Helen Rollison & Katherine Fenner

Pharmaron UK Ltd, Hertford Road Hoddesdon Hertfordshire, EN11 9FH, UK

Evolving Bioanalysis Standards for Highly Bound Drugs

Recent updates under the ICH M12 guideline have removed the 0.01 unbound fraction threshold for reportable protein binding. This regulatory change places new emphasis on the accuracy of plasma protein binding (PPB) assays, especially for highly bound, lipophilic compounds that often challenge conventional techniques.

This poster outlines practical strategies for accurately measuring low unbound drug fractions and evaluates methods aligned with current ICH expectations.

Understanding the Impact of ICH M12 on Binding Assays

With the elimination of a minimum reportable free fraction, even drugs with <0.001 unbound fractions must now be quantified. This has significant implications:

Increased scrutiny of protein binding method validation
Higher demands for precision at low detection levels
Regulatory expectations for assay reproducibility, especially in submission datasets

The ICH M12 Step 4 guideline outlines updated bioanalytical validation principles, expanding the scope for fraction unbound (fu) reporting.

Read ICH M12 Official Document

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Knowledge Center

DMPK Services

Bioanalysis Services

Cellular Disease Models

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Current Methods for Plasma Protein Binding Studies

Equilibrium Dialysis: The Established Gold Standard

This method works well for compounds with fu ≥ 0.001. However, it suffers from:

Non-specific binding to the device or materials
Compound loss in the buffer chamber
Limited detection at low fu values
Time-consuming equilibrium requirements

Flux Dialysis: Optimized for Challenging Molecules

For highly bound compounds or drugs with low MS detectability:

Plasma on both sides of the membrane equalizes the nonspecific loss
No equilibrium needed — simplifies the protocol
Higher concentration in the receiver chamber improves sensitivity
Validated using published scaling factors (e.g., 3590 s from Kalvass et al.)

Flux dialysis provides robust and reproducible data for fu <0.001, enabling accurate submission-ready values.

Practical Assay Selection Guidance

Compound Property	Recommended Method
fu ≥ 0.001	Equilibrium Dialysis
fu < 0.001	Flux Dialysis
High non-specific binding	Flux Dialysis
MS sensitivity limits	Flux Dialysis

References

Ensure Your PPB Assays Meet the New ICH Standards

Download our poster to explore detailed protocols and validation strategies that meet new ICH expectations. Discover how Pharmaron supports drug developers with high-sensitivity PPB data that passes regulatory review.