Body clear- 1 Body clearance OCT 2010 PL Toutain

Body clear- 2 Body clearance Body clearance, plasma (blood) clearance, systemic clearance, total clearance...

Body clear- 3 A fundamental relationship in steady-state conditions Drug rate in Drug rate out Dosage regimenClearance ClinicianPatient's eliminatory process

Body clear- 4 A fundamental relationship Dose = Body clearance x therapeutic concentration Bioavailability A dose can be determined rationally using a PK/PD approach !

Body clear- 5 Why is clearance a fundamental PK parameter ? Clearance is the only parameter measuring the ability of a body (or an organ) to eliminate a drug Ability is not synonymous with rate of elimination (i.e. dx / dt) !

Body clear- 6 Body clearance Total clearance is a proportionality factor which relates the rate of drug elimination to a drug (plasma, blood) concentration Rate of drug elimination = Cl x C

Body clear- 7 2 basic questions What is the rate of drug elimination? Cl x C What is the amount of drug in the body? Vss x C

Body clear- 8 Why clearance should be evaluated ? for a practical purpose : dose computation for a mechanistic purpose: interpretation

Body clear- 9 Should be evaluated for any new drug entity Should be interpreted in physiological terms Body clearance

Body clear- 10 How to measure body clearance ? Cl body = Dose (IV) / AUC (plasma, blood) An IV administration is required !

Body clear- 11 Amount eliminated from 0 to infinity :   dx =  Cl TOT C dt = Cl TOT  C dt 0 0 Dose AUC 0    Measure of the body clearance Where does the relation Cl = come from ? Dose AUC By definition Cl TOT =  dx = Cl TOT x C x dt dx/dt C Cl TOT = =   dx  C dt 0  0 

Body clear- 12 Measure of the body clearance Administration by IV of a known dose Measure of plasma (blood) concentration Units of AUC (mg x L -1 ) x h = mg x h. L -1 !

Body clear- 13 Measure of body clearance Accuracy of the dose Physicians (8)Pharmacists (4) Mean Range SD Target dose

Body clear- 14 Why is an IV PK study required ? To provide essential PK drug parameters Cl body Volume of distribution True half-life of elimination (substance) To properly investigate the extravascular route to measure absolute bioavailability to determine the rate of absorption

Body clear- 15 Measure of the body clearance Is it possible to determine body clearance when IV administration is impossible? Yes in some special circumstances

Body clear- 16 How to measure body clearance when IV administration is impossible ? Principle : Cl body = Cl renal + Cl liver + Cl other if Cl liver and Cl other = 0 then Cl body = Cl renal Thus Cl body = Amount excreted in urine per time unit Plasma concentration

Body clear- 17 Clearance computation from excretion rate Definition : Cl = thus dx/dt = Cl * plasma concentration of the form y = a * x with a = clearance dx/dt (excretion rate) plasma concentration

Body clear- 18 Clearance computation from excretion rate Slope = clearance Excretion rate (dx/dt) Plasma concentration Possible non-linearity

Body clear- 19 Physiological interpretation of blood (plasma) clearance

Body clear- 20 Is a Amiodarone plasma clearance of 1.9 mL/kg/min high, low or very low ? ?

Body clear- 21 Is a Amiodarone plasma clearance of 1.9 mL/kg/min high, low or very low ? Is a Amiodarone plasma half-life of 25 days short, long or very long ? ? YES, very long !

Body clear- 22 Is a Amiodarone plasma clearance of 1.9 mL/kg/min high, low or very low ? Difficult to answer because clearance has the dimension of a flow

Body clear- 23 Why is clearance a flow ? By definition : Cl = = = VT -1 flow How to give a physiological meaning to this flow ? by modeling clearance in terms of physiological blood flow dx / dt C MT -1 MV -1

Body clear- 24 Definition : dx/dt / Driving concentration Model : Q x E Q : cardiac output E : extraction ratio o o Body clearance Concept not to confuse Computation method : Dose / AUC

Body clear- 25 Plasma clearance Cl = = Q x E = definition modelcomputation method dx/dt C Dose AUC ° Concept not to confuse

Body clear- 26 What reference system for plasma (blood) clearance?

Body clear- 27 Reference system: clearance vs. half-life Blood (plasma) Clearance (L/min/kg) Blood (plasma) Half-life (min) Watch Cardiac output

Body clear- 28 Heart Clearing organs (liver, kidney,…) Cl body = Q x E Q = cardiac output = 180 BW with BW= kg et Q= ml/kg/min E = overall extraction ratio E o o o Physiological interpretation of plasma (blood) clearance

Body clear- 29 The body (blood) clearance Model to interpret blood clearance Cl body = Q cardiac output x E body flowflowno unit Operationally, clearance is the blood (plasma) volume which is totally cleared of the analyte during a time unit °

Body clear- 30 Interpretation of body clearance Interpretation of body clearance consists of calculating an extraction ratio E body = Body clearance (blood) Cardiac output

Body clear- 31 From literature From allometric relationship Q (mL/kg/min) = 180 BW (kg) Example : a 70 kg BW man Q = 180 x = 180 x 0.44 = 80 mL/kg/min ° ° Cardiac output 5.6L/min

Body clear- 32 plasma clearance (ml/kg/min) Cardiac output (ml/kg/min) Overall extraction ratio (%) Rem. 1 : half-life (min) Rem. 2 : we assume Cl blood = Cl plasma i.e. C blood =C plasma Penicillin x Gentamicin 3.1 poids (kg) Oxytetracycline 4.0 ­ 100 ml/kg/min Tylosin kg Interpretation of body clearance

Body clear- 33 Clairance vs temps de demi-vie Amiodarone Clairance: 1.9 ml/kg/min Temps de demi-vie: 25 jours Amikacine Clairance: 1.3 ml/kg/min Temps de demi-vie: 2.3 heures

Body clear- 34 Body (total) clearances Except for drugs metabolized in blood or lungs, body clearance cannot be higher than cardiac output D (L/min/kg) = 180 BW with BW in kg BW (kg) Cl max (ml/kg/min) Assumption C blood = C plasma

Body clear- 35 Is the Amiodarone blood clearance high or low ? cardiac output:  70 mL/kg/min extraction ratio:  2.7% body clearance 1.9 mL/kg/min

Body clear- 36 Is E = 2.7% low or high ?  Need of critical value Is the Amiodarone extraction ratio high or low ?

Body clear- 37 Clearances are additive Cl body = Cl renal + Cl hepatic + Cl other

Body clear- 38 Organ blood flow (% of cardiac output) Liver:30% Kidney:20%

Body clear- 39 Extraction ratio Critical values High > 0.7 Low < 0.3 this is not "magic" cutoff

Body clear- 40 Interpretation of an overall extraction ratio Drug with a high overall E Drug with a low overall E 30 % E  70% 20% E  70% Overall E = 35% 30 % E  30% 20% E  30% Overall E = 15%

Body clear Is the body clearance high or low ? For an organ : E is high if > 0.7 E is low if < 0.3 Cl body = Cl hepatic + Cl renal + Cl other Q body x E overall = Q h x E h + Q r x E r +  with Q h = 0.3 Q total Q r = 0.2 Q total o o o o o o o Interpretation of body clearance

Body clear Is the body clearance high or low ? Cl body high if > 35% of cardiac output Q tota l x E overall =0.3Q total x Q total x 0.7 Q total x E overall = 0.35 Q total o o o o o E overall = 0.35 (35%) Interpretation of body clearance kidney liver

Body clear- 43 Critical extraction ratios [0.3 et 0.7] Clint/Qh ° Eh Rowland p Eh = fu x Clint Q h + fu x Clint ° Extraction ratio

Body clear Is the body clearance high or low ? Cl body low if < 15% of cardiac output Q total x E overall = 0.3Q total x Q total x 0.3 Q total x E overall = 0.15 Q total o o o o o E overall = 0.15 (15%) Interpretation of body clearance

Body clear Is the body clearance (mL/kg/min) high, medium or low ? BW (kg) Cl high (E=0.35) Cl medium (E= 0.15) Cl low (E= 0.05) Interpretation of body clearance

Body clear- 46 Comparison of 2 molecules in the same class Application of clearance concept

Body clear- 47 Comparison of 2 drugs (MW=500 & 600) in the same class Plasma clearance (ml/kg/min) Plasma cardiac output Overall extraction ratio (%) Drug A BW (0.23/80)x100= 0.29% Drug B mL/kg/min (0.60/80)x100= 0.75% Interpretation of plasma clearance

Body clear- 48 Drug A Drug B Plasma clearance (mL/kg/min) Overall extraction ratio (%)0.29%0.75% Interpretation of plasma clearance Conclusion: very low for both drugs 3 times lower for Drug A than for Drug B Comparison of 2 drugs in the same class

Body clear- 49 Drug A vs Drug B Overall extraction ratio is three times lower for Drug A than for Drug B Was it possible to predict such a difference ? Probably : by in vitro assay What is the origin of the difference?

Body clear- 50 Drug A vs. Drug B As MW is high : Cl body = Cl h Both drugs have a low extraction ratio thus : Cl h = Q h x = fu Cl int fu x Cl int Q h + fu x Cl int ° ° fu and Cl int can be determined by in vitro assays Assumption:

Body clear- 51 Drug A vs. Drug B: fu or Clint ?

Body clear- 52 Drug A vs Drug B: fu? Drug binding to circulating protein In vitro studies e.g. equilibrium dialysis

Body clear- 53 Drug A vs. Drug B: Clint? Hepatic clearance Cl int = Vmax Km + Cfree metabolic capacity drug affinity Catalysis Binding

Body clear- 54 Vmax or Km? Penetration Catalysis (Vmax) Binding (Km) Energy level Low /reversible High/covalent Surface porperties Core properties Polarity, hydrophobicity, lipophilicity Reactivity, electronic property Steric hindrance topography

Body clear- 55 Drug A vs Drug B Origin of the difference fu : drug binding plasma protein Km: drug affinity for metabolic enzyme Vmax : catalytic efficiency

Body clear- 56 Application of the clearance concept Interspecies comparison

Body clear- 57 Plasma (blood) clearance (ml/kg/min) Cardiac output (ml/kg/min) Extraction ratio 0.25 (80 kg) (20 kg) (10g) Conclusion : all three species had the same overall capacity to eliminate the drug Interspecies comparison Application of the clearance concept

Body clear- 58 Interspecies dose extrapolation Application of the clearance concept

Body clear- 59 Goal : to obtain the same exposure (AUC) for the 2 species Dose = AUC x Cl AUC man = AUC rat = = Dose man = Dose rat Cl rat Dose man Cl man Cl man xDose rat Cl rat Interspecies dose extrapolation

Body clear- 60 Interspecies dose extrapolation Dose species1 = Dose species2 x Cl species1 Cl species2

Body clear- 61 What to do when the clearance for man is unknown ? allometric approach Extrapolation of the dose from animal to man Interspecies dose extrapolation

Body clear- 62 The allometric approach empirical method of extrapolation based on the underlying anatomical, physiological and biological similarities in animals successful for drugs which are highly dependent on renal clearance, hepatic blood flow or metabolic clearance by reaction other than MFO system

Body clear- 63 Allometric relationship Log parameter Log BW Log y = a + b Log BW y = coefficient xBW b Interspecies dose extrapolation

Body clear- 64 Interspecies dose extrapolation Which dose of ketoprofen in goat ? : 3 mg/kg/24 h ; Cl = 0.17L/kg/h : Cl = 0.74 L/kg/h Dose goat = Dose cattle (3mg/kg) x Cl goat (0.74L/kg/h) Clearance cattle (0.17 L/kg/h) Dose goat = 13 mg/kg

Body clear- 65 Acute toxicity of anticancer drugs human versus mouse Dose RatioAUC Ratio

Body clear- 66 To predict that a drug can be successfully marketed as an oral dosage form Application of the clearance concept

Body clear- 67 Why can a drug not be administered by oral route? Not absorbable formulation, solution P-glycoprotein… First pass effect in the digestive tract in the gut lumen liver Application of the clearance concept

Body clear- 68 Can a drug be successfully marketed as an oral dosage form? How to answer this question only from IV data  by measuring total and renal clearance to evaluate the non renal clearance

Body clear- 69 vena cava Liver DT Absorption portal vein Absolute bioavailability F = 1 - (f 1 + f 1 f 2 ) F = 0.25 Fraction eliminated (f 2 ) by first pass effect f 2 = 0.5 Fraction not absorbed (f 1 ) f 1 = 0.5 Hepatic first pass effect

Body clear- 70 Fmax = 1 - E h Liver Fmax = 1 - E h Dose Eh Fraction eliminated by first pass effect Goal: to know Eh Hepatic first pass effect

Body clear- 71 Cl h = Q h x E h E h = Cl h / Q h Fmax = 1 - E h = 1 - [Cl h / Q h ] Maximal oral bioavailability Goal : to know Cl h Hepatic first pass effect

Body clear- 72 YES: by measuring the total and renal clearances to evaluate the non renal clearance (hepatic) Cl tot = Cl h + Cl r + Cl other Cl tot = Dose / AUC Clrenal = = Cl h = Cl tot - Cl r Can we predict whether a drug is administrable by oral route? dX/dt (urine) AUC total amount excreted in urine AUC

Body clear- 73 How to predict hepatic and renal clearance to evaluate Fmax 1. Experimental data : 20 kg dose : 15 mg/kg, AUC plasma = 500  g.min.ml -1 fraction eliminated by urine : 0.5 mg/kg 2. Literature data : Qh = 30 mL/kg/min ° Can a drug be administered by oral route?

Body clear Computation Cl tot = 15 mg/kg / 500  g.min.ml -1 = 30 ml/kg/min Cl r = 0.5 mg/kg / 500  g.min.ml -1 = 1 ml/kg/min Cl h = 30-1 = 29 ml/kg/min 3. Interpretation Fmax = 1 - Cl h /Q h Fmax = /30 = 0 4. Conclusion This drug cannot be administered by oral route ° Can a drug be administered by oral route?

Body clear- 75 If Cl plasma  Cl blood it is necessary to evaluate the Cl blood Necessary to know the ratio: blood plasma or B/P Can a drug be administered by oral route?

Body clear- 76 The blood to plasma concentration Permits conversion of the more easily measured plasma concentrations and their derived parameters into a blood concentration measurement Application: calculate Fmax, the maximal oral bioavailability

Body clear- 77 Blood or plasma clearance ?

Body clear- 78 Blood or plasma clearance? Blood Cb > Cp and redistribution (departitionning) occurs during transit throughout the clearing organ (10 sec for liver, 2 sec for kidney cortex, 30 sec for kidney medulla)  interpretation in terms of blood flow (ex.: labetol) Plasma Cp = Cb (antipyrine/alcool) Cp > Cb (maximum bias of 40%) Cb > Cp (slow reequilibration between red blood cells and plasma during organ transit  interpretation in terms of plasma flow (ex.: PAH)

Body clear- 79 Answer from in vitro study only Can a drug be administered by oral route?

Body clear- 80 Cl h = Q h x fu x Clint Q h + fu x Clint o o Model for hepatic clearance (Cl h ) fu : free fraction Clint : intrinsic clearance Fmax = 1 - Eh Can a drug be administered by oral route? Eh

Body clear- 81 Clint fu, Q h E h Q h Cl h hepatic clearance to evaluate indirectly Cl renal Cl total Dosage regimen, etc. ° ° Why know the intrinsic clearance from an in vitro study? Can a drug be administered by oral route?

Body clear- 82 Evaluation of a dose Application of the clearance concept

Body clear- 83 A fundamental relationship in steady-state conditions Drug rate in Drug rate out Dosage regimenClearance ClinicianAnimal's eliminatory process

Body clear- 84 Under equilibrium conditions entry rate = exit rate = Cl x Css, therap F x dose dosage interval Plasma clearance and dose estimation

Body clear- 85 Dose dosage interval Cl x Css therap. Bioavailability = Plasma clearance and dose estimation

Body clear- 86 dose loading dosing troughs and doseintervalpeaks Cl/F Vss/F t1/2 Vss/F & t1/2 Pharmacokinetics and dosage regimen

Local (BBB…) (drug targeting; ADR) overall Plasma Binding Barrier systemic factor Poor oral bioavailability Poor exposure Absorption Distribution clearance AUC Half-life Transporters Cell junctions Physicochemical

Clearance Hepatic Renal Metabolic Biliary CYP450 Others Polymorphism 1A2;2C9;2C19;2D6;3A4 IR Induction Inhibition CAR AHR PXR Sulfate Glucuronide Amino-acid

Body clear- 89 The body clearance: summary The only parameter expressing the body's ability to eliminate a drug comparison between drugs interspecies comparison Can be interpreted in physiological terms looking for limiting factors cardiac output metabolism, binding

Body clear- 90 The body clearance: summary Allows us computation of a dose if the therapeutic drug concentration is known Needs to be evaluated in vivo requiring an IV study Can be estimated from in vitro