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Research ArticleArticle

SUBSTRATE DEPLETION APPROACH FOR DETERMINING IN VITRO METABOLIC CLEARANCE: TIME DEPENDENCIES IN HEPATOCYTE AND MICROSOMAL INCUBATIONS

Hannah M. Jones and J. Brian Houston
Drug Metabolism and Disposition September 2004, 32 (9) 973-982; DOI: https://doi.org/10.1124/dmd.104.000125
Hannah M. Jones
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This article has a correction. Please see:

  • CORRECTION to September Issue of Drug Metabolism and Disposition - November 01, 2004

Abstract

The substrate depletion method is a popular approach used for the measurement of in vitro intrinsic clearance (CLint). However, the incubation conditions used in these studies can vary, the consequences of which have not been systematically explored. Initial substrate depletion incubations using rat microsomes and hepatocytes were performed for eight benzodiazepines: alprazolam, clobazam, clonazepam, chlordiazepoxide, diazepam, flunitrazepam, midazolam, and triazolam. Subsequent predictions of in vivo CLint (ranging from 3 to 200 ml/min) and hepatic clearance (CLH) (ranging from 0.3 to 15 ml/min) demonstrated that the general predictive ability of this approach was similar to that of the traditional metabolite formation method. A more detailed study of the substrate depletion profiles and CLint estimates indicated that the concentration of enzyme used is of particular importance. The metabolism of triazolam, clonazepam, and diazepam was monoexponential at all cell densities using hepatocytes; however, with microsomes, biphasic depletion was apparent, particularly at higher microsomal protein concentrations (2-5 mg/ml). Enzyme activity studies indicated that enzyme loss was more pronounced in the microsomal system (ranged from 8 to 65% activity after a 1-h incubation) compared with the hepatocyte system (approximately 100% activity after a 1-h incubation). For clonazepam (a low clearance substrate), these biphasic profiles could be explained by loss of enzyme activity. To ensure accurate predictions of in vivo CLint and CLH when using the substrate depletion approach, based on the results obtained for this class of drugs, it is recommended that low enzyme concentrations and short incubation times are used whenever possible.

Footnotes

  • ↵1 Current address: Department of Non-Clinical Drug Safety, Drug Metabolism and Pharmacokinetics, F. Hoffmann La Roche, Basel, Switzerland.

  • This work was funded by a consortium of pharmaceutical companies (Astra-Zeneca, Bristol Myers Squibb, GlaxoSmithKline, F. Hoffmann-La Roche, Novartis, Pfizer, and Servier) within the Centre for Applied Pharmacokinetic Research at the University of Manchester.

  • Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.

  • doi:10.1124/dmd.104.000125.

  • ABBREVIATIONS: CLint, intrinsic clearance; CLH, hepatic clearance; DMF, dimethylformamide; HPLC, high-performance liquid chromatography; AIC, Akaike information criterion; NADP, nicotinamide adenine dinucleotide phosphate.

    • Received April 7, 2004.
    • Accepted June 8, 2004.
  • The American Society for Pharmacology and Experimental Therapeutics
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Drug Metabolism and Disposition: 32 (9)
Drug Metabolism and Disposition
Vol. 32, Issue 9
1 Sep 2004
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Research ArticleArticle

SUBSTRATE DEPLETION APPROACH FOR DETERMINING IN VITRO METABOLIC CLEARANCE: TIME DEPENDENCIES IN HEPATOCYTE AND MICROSOMAL INCUBATIONS

Hannah M. Jones and J. Brian Houston
Drug Metabolism and Disposition September 1, 2004, 32 (9) 973-982; DOI: https://doi.org/10.1124/dmd.104.000125

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Research ArticleArticle

SUBSTRATE DEPLETION APPROACH FOR DETERMINING IN VITRO METABOLIC CLEARANCE: TIME DEPENDENCIES IN HEPATOCYTE AND MICROSOMAL INCUBATIONS

Hannah M. Jones and J. Brian Houston
Drug Metabolism and Disposition September 1, 2004, 32 (9) 973-982; DOI: https://doi.org/10.1124/dmd.104.000125
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