title: Does the well-stirred model assess the intestinal first-pass effect well?
abstract: The pre-systemic intestinal extraction ratio (E(g)) has been estimated by an equation based on the well-stirred model, which does not have a term of membrane transport. In this report, we have identified the application limitations of the well-stirred model equation to assess the pre-systemic intestinal extraction ratio. The E(g) of metoprolol (CYP2D6 substrate) was assessed by three methods. Intrinsic clearances for metoprolol metabolism in hepatic and gastrointestinal microsomes were from a published report. Method 1 (model-independent method): the E(g) of 0.228 was obtained according to the equation, F = F(f) x (1 - E(g)) x F(h), where F, F(f) and F(h) were the bioavailability, the fraction entering the intestinal tissue and the hepatic availability, respectively. Method 2: the E(g) of 0.0071 was calculated according to the well-stirred model equation, and was much lower than the value of 0.228. Method 3: the E(g) of 0.213 was obtained by the transport-metabolism-flow (TMF) model equation, and was much closer to the value of 0.228 obtained by the model-independent method than the E(g) of 0.0071 calculated by the well-stirred model equation. Therefore, we propose that the factor of membrane transport process be incorporated into the pharmacokinetic model for the assessment of the pre-systemic intestinal extraction ratio.
authors.affiliation: Department of Drug Absorption and Pharmacokinetics, School of Pharmacy, Tokyo University of Pharmacy and Life Science (TUPLS), 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan. mizuma@ps.toyaku.ac.jp
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizuma
authors.forename: Akira
authors.initials: A
authors.lastname: Tsuji
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hayashi
mesh_terms: D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology*; D008657:Metabolic Clearance Rate / Q000187:drug effects / Q000502:physiology*; D008954:Models, Biological; D004364:Pharmaceutical Preparations / Q000378:metabolism*
chemical_list: D004364:Pharmaceutical Preparations