title: The assessment of bioavailability in the presence of nonlinear elimination.
abstract: The simultaneous administration of an oral dose and intravenous tracer dose, as a method to determine bioavailability, was examined by means of computer simulation for drugs exhibiting Michaelis-Menten type elimination. A physiological pharmacokinetic model parameterized for man and including first-order absorption and elimination solely from the liver was employed. This tracer method provided good estimates of the true availability, with an error of 6% or less, over a wide range of dosing and dispositional conditions. Poorer estimates were noted when large doses of drugs with very short half-lives were considered. This poor performance was improved by administering the intravenous tracer at some time after the oral dose but an a priori basis for establishing this time was not apparent. The tracer method, therefore, appears to be a robust means of assessing, in man, oral bioavailability in the presence of Michaelis-Menten type elimination for drugs characterized by the general properties of the physiological model employed and with half-lives in excess of approximately 40 min. These findings together with the statistical power and simplicity of performance of the tracer method indicate that it is a valid technique for the assessment of bioavailability under a wide range of kinetic conditions.
authors.affiliation: epartment of Pharmacology, Vandervilt University, Nashville, Tennessee 37232.
authors.forename: S D
authors.initials: SD
authors.lastname: Hall
authors.forename: C B
authors.initials: CB
authors.lastname: McAllister
authors.forename: G R
authors.initials: GR
authors.lastname: Wilkinson
mesh_terms: D001682:Biological Availability; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008433:Mathematics; D008954:Models, Biological