Clinical Pharmacokinetics

, Volume 40, Issue 8, pp 565–572

Measures of Exposure versus Measures of Rate and Extent of Absorption

  • Mei-Ling Chen
  • Lawrence Lesko
  • Roger L. Williams
Leading Article

DOI: 10.2165/00003088-200140080-00001

Cite this article as:
Chen, ML., Lesko, L. & Williams, R.L. Clin Pharmacokinet (2001) 40: 565. doi:10.2165/00003088-200140080-00001


Regulatory assessment of bioavailability and bioequivalence in the US frequently relies on measures of rate and extent of absorption. Rate of absorption is not only difficult to measure but also bears little clinical relevance. This paper proposes that measures of bioavailability and bioequivalence for drugs that achieve their therapeutic effects after entry into the systemic circulation are best expressed in terms of early [partial area under the concentration-time curve (AUC)], peak plasma or serum drug concentration and total AUC exposure for a plasma or serum concentration-time profile. With suitable documentation, these systemic exposure measures can be related to efficacy and tolerability outcomes. The early measure is recommended for an immediate release drug product where a better control of drug absorption is needed, for example to ensure rapid onset of a therapeutic effect or to avoid an adverse reaction from a fast input rate. The 3 systemic exposure measures for bioavailability and bioequivalence studies can provide critical links between product quality and clinical outcome and thereby reduce the current emphasis on rate of absorption.

Copyright information

© Adis International Limited 2001

Authors and Affiliations

  • Mei-Ling Chen
    • 1
  • Lawrence Lesko
    • 2
  • Roger L. Williams
    • 3
  1. 1.Office of Pharmaceutical Science (HFD-350), Center for Drug Evaluation and ResearchFood and Drug AdministrationRockvilleUSA
  2. 2.Office of Clinical Pharmacology and Biopharmaceutics, Office of Pharmaceutical Science, Center for Drug Evaluation and ResearchFood and Drug AdministrationRockvilleUSA
  3. 3.The United States PharmacopeiaRockvilleUSA

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