Improving In Vitro-In Vivo Extrapolation of Clearance Using Rat Liver Microsomes for Highly Plasma Protein-Bound...

Area of Science:

• Pharmacokinetics and Drug Metabolism
• Drug Discovery and Development

Background:

• The well-stirred model (WSM) is standard for predicting in vivo hepatic clearance from in vitro liver incubations.
• WSM shows poor in vitro-in vivo correlation (IVIVC) for acidic compounds, unlike neutral and basic compounds.
• High plasma protein binding of acids is hypothesized as a cause for the IVIVC disconnect.

Purpose of the Study:

• To investigate the impact of plasma protein binding on the IVIVC of acidic compounds.
• To develop methods for improving the accuracy of in vitro-in vivo extrapolation (IVIVE) for drug clearance.
• To establish a correction for in vitro clearance estimations based on plasma protein binding.

Main Methods:

• Incubation of proprietary compounds with rat liver microsomes in the presence and absence of plasma.
• Measurement of intrinsic clearance and calculation of fraction unbound in plasma (fu_p).
• Development of an empirical, nonlinear correction equation based on fu_p for clearance predictions.

Main Results:

• Plasma addition significantly improved IVIVC for highly protein-bound acidic compounds (fu_p <1%).
• A minor impact was observed for moderately bound compounds (fu_p ≥1%).
• An empirical correction equation was derived to adjust unbound intrinsic clearance (CL_int,u) based on fu_p.

Conclusions:

• Supplementing microsomal incubations with plasma enhances the estimation of metabolic clearance for highly bound compounds.
• The derived empirical equation improves clearance predictions for standard buffer-only incubations.
• This approach offers a way to refine IVIVE, particularly for acidic drugs with high plasma protein binding.