TY - JOUR T1 - Pharmacokinetic model of presystemic metabolism. JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 193 LP - 196 VL - 6 IS - 2 AU - W A Colburn AU - M Gibaldi Y1 - 1978/03/01 UR - http://dmd.aspetjournals.org/content/6/2/193.abstract N2 - A pharmacokinetic perfusion model is presented that describes the disposition of drugs that are subject to both first-pass hepatic and intestinal epithelial metabolism. Equations are developed to estimate hepatic and intestinal epithelial clearances by determining drug concentrations as a function of time in both portal and peripheral vein blood after oral and iv administration, and by determining or estimating the flow rate of blood perfusing the gastrointestinal tissues. A method that can be used, under the stated conditions, to approximate the systemic availability after oral administration of drugs subject to presystemic metabolism is also developed. ER -