In vitro–in vivo extrapolation of metabolic clearance using human liver microsomes: factors showing variability and their normalization

Abstract

1. In vitro–in vivo extrapolation (IVIVE) using human liver microsomes has been widely used to predict metabolic clearance, but some of the factors used in the process of prediction show variability for the same compound: notably, microsomal intrinsic clearance values corrected by the unbound fraction (CL_{int, u}), physiological parameters used for scale-up, and the source of in vivo clearance data.

2. The purpose of this study was to assess the correlation between in vitro and in vivo CL_int with a focus on factors showing variability using four cytochrome P450 (CYP)3A substrates.

3. We surveyed in vivo clearance values in literature and also determined the microsomal CL_{int, u} values. A scaling factor (SF_direct) was defined as in vivo CL_int divided by the microsomal CL_{int, u}, which ranged from 1190 to 2310 (mg protein per kg body weight). The application of a mean SF_direct of 1600 (mg protein per kg body weight) and further normalization by the microsomal CL_{int, u} values of midazolam, the most commonly used substrate, resulted in improved prediction accuracy for CL_{int, u} values from various microsomal batches.

4. The results suggest the normalization of variability might be useful for predicting the in vivo CL_int.

Keywords:

• In vitro-in vivo extrapolation
• metabolic clearance
• human liver microsomes
• CYP3A
• midazolam
• variability
• scaling factor

Acknowledgments

We thank Akiyo Kaji for technical support in bioanalysis and Jacob Davis for useful advice in the preparation of this article.

Disclosure statement

No potential conflict of interest was reported by the author(s).