# PharmPK Discussion - Extraction Ratio

PharmPK Discussion List Archive Index page
• On 10 Jan 2013 at 17:41:00, Xinting Wang (wxinting1986.-at-.gmail.com) sent the message
`Dear all,Can anybody please help explain the following equation to calculate ER(extraction ratio)? I saw that many paper calculating CLorgan used thisequation but none of them provided explanation to it.ER =fu*CLint/(Qorgan + fu*CLint)Where,ER= Extraction RatioCLint= intrinsic clearanceQorgan=organ blood flowfu=unbound fraction of the compoundThanks and RegardsXinting[See also http://www.boomer.org/c/p4/c17/c1704.html- db]`
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• On 10 Jan 2013 at 11:07:04, Chris (chris_kemper.-a-.pharmanavigatorsllc.com) sent the message
`The following message was posted to: PharmPKXinting:That equation is derived from the basic relationshipER = (Cin-Cout)/Cin,Where Cin and Cout are the concentrations in and out of the clearingorgan.There are several intermediate equations in the derivation that can befoundin many PK texts, including Pharmacokinetic and Pharmacodynamic DataAnalysis by Gabrielson and Weiner (Apotekarsocietetan 2001)ChrisChristopher J. Kemper, Ph.D.Pharma Navigators, LLCDMPK/Bioanalytical ConsultingAlliance Management/Business Analysis`
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• On 10 Jan 2013 at 16:40:00, William Wolowich (wwolowic.-at-.nova.edu) sent the message
`The following message was posted to: PharmPKXinting: Do the math:Er,organ = CLorgan / Qorgan (for the liver is Er = CLh/LBF)Er = (Qorgan*fu*CLint/ (Qorgan + fu*CLint)) / QorganEr = fu*CLint / (Qorgan + fu*CLint)William R. Wolowich, Pharm.D., R.Ph.College of PharmacyNova Southeastern Universitywwolowic.-a-.nova.edu[For the well-stirred model, see also http://www.boomer.org/c/p4/ja/Fig1702/Fig1702.html- db]`
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• On 15 Jan 2013 at 10:51:08, "J.H.Proost" (j.h.proost.-at-.rug.nl) sent the message
`Dear Zinting,In addition to the useful link provided by David Bourne, the followingmay be helpful to understand the relationship describing the extractionratio.1) total hepatic blood flow (QH),2) fraction unbound (fU) or the extent of drug binding to bloodconstituents.3) free intrinsic clearance (CLint) or the rate-limiting step in druguptake from blood, intracellular transport, metabolism.Consider a drug molecule in the hepatic sinusoids: two things mayhappen:a) the molecule escapes hepatic extraction: this chance is proportionalto Q_H (and the drug concentration in the blood);b) the molecule enters a hepatocyte and is metabolized; this chance isproportional to fu (only free drug enters the liver) and proportional toCLint (and the drug concentration in the blood).So, the chance that a molecule is extracted from the blood, is thechance of b) divided by the som of a) and b), or (after dividing both bythe blood concentration):E_H = (fu * CLint) / (Q_H  +  fu * CLint).This is a very simplistic derivation, and should not be regarded as aformal proof, but for understand the relationship between the threefactors (Q_H, fu, CLint) and the extraction ratio it is quite useful inmy teaching experience.best regards,Hans ProostJohannes H. ProostDept. of Pharmacokinetics, Toxicology and TargetingUniversity Centre for PharmacyAntonius Deusinglaan 19713 AV Groningen, The Netherlands`
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