Clinical Drug Development: Phase II and PK/PD. 1 Thomas D. Szucs

Transcription

1 Clinical Drug Development: Phase II and PK/PD 1

2 Discussion Topics Introduction Definitions Transport Across Membranes Absorption, Distribution, Elimination Processes, Models, Descriptors, Influence on Cp,T-profiles Multiple Dosing Accumulation Application of PK in Drug Development PK Principles 2

3 THE THERAPEUTIC TRIANGLE THERAPEUTICS PHARMACODYNAMICS PHARMACOKINETICS EFFECT CONCENTRATION DOSE APV_Lecture_2006_1 3

4 Definitions: Pharmacokinetics PHARMACOKINETICS deals with time courses of drug concentrations in the body. Key question: What does the body do with the drug? Study of absorption, distribution and elimination processes of drugs and derived metabolites, their time dependence and their influence on concentration-time courses Goal: To define the relationship between mode, frequency of administration and the resulting concentrations (dose-concentration relationship) Importance: Concentration drive duration and intensity of effects 4 PK Principles

5 Determinants for Pharmacokinetic Behavior of a Drug physico-chemical properties dosage form route of administration anatomical and physiological conditions of body genetic and environmental influencing factors concomitantly administered drugs unfavorable PK properties can limit or prevent clinical use of a drug PK Principles 5

6 Drug Transport through Membranes Lumen paratranscellular cellular diffusion active Efflux pumps Pores Metabolism vesicular P-gp Epithelial Cell CYP3A D+ Blood 6

7 Influence of Concentration on Passive Diffusion and Carrier-Mediated Transport passive diffusion Initial Rate of Trsp Vmax active transport Km Concentration V V Km = max C + C Vmax Km maximum transport velocity concentration at half-maximum transport rate 7

8 Adsorption 8

9 Absorption The absorption step includes all processes occurring to transported drug from the site of administration (e.g., small intestine) to the site of measurement, usually the blood stream. Site of administration Absorption Site of measurement/ blood stream 9

10 Mass Balance Considerations to Derive Time Courses of Drug in the Body Simple Model Drug at Absorption Site Absorption Drug in Body Excretion Metabolism Excreted Drug Metabolites Dose = Amount at absorption site + Amount in Body + Amount metabolized + Amount excreted D = Aa + Ab + Am + Ax Rate of change of drug amount in body = Rate of absorption - Rate of metabolism - Rate of excretion dab = dt daa - dt dae - dt dax dt Relationship is independent from nature of absorption and elimination processes.

11 Time Courses of Drug and Metabolites Drug at Absorption Site Drug in Body Excreted Drug Percent of Dose Drug at Absorption Site Drug in Body Metabolite in Body Excreted Metabolite Excreted Metabolite Excreted Drug 20 Metabolite in Body Time, hours 11

12 Factors Influencing Concentration- Time Profiles: Absorption Rate Concentration in Blood 0 0 Time 12

13 Factors Influencing Concentration- Time Profiles: Dose 5 Concentration in Blood F Dose = CL AUC 0 Time 13

14 Absorption Parameters Aspects Description (Parameters) Influencing Factors (for oral absorption) Rate Extent ka, t max, C max Bioavailability F 1), Exposure AUC, C max release rate of drug from dosage form fasted or non-fasted gastric emptying, GI motility; other drugs; gut blood flow Compliance; release of drug from dosage form; stability in GI tract; GI permeability (passive, active); first-pass effect (hepatic, intestinal) 1) comparison of dose-corrected AUCs after test and comparator formulations 14

15 Oral Absorption Process: Barriers To Site of Measurement Liver Hepatic First-Pass Extraction Portal Vein Gut Wall Permeation +Active Processes Solubility Stability Gut Lumen Metabolism Gut Flora To Feces 15

16 Physiology of Gastrointestinal Tract Segment ph Residence time Remarks Stomach h ph dependent on food intake, age, comedication Small intestine 3 6 h Duodenum h Jejunum ~7 Ileum ~7 Colon h residence time dependent on fasting state, galenical form 16

17 Rate-Limiting Steps in Absorption (1) Absorption Limitations Dissolution Permeability Blood Flow (Perfusion) Trsp GUT LUMEN GUT LUMEN 17 GUT WALL PORTAL BLOOD adapted from Rowland, Thomas Tozer, D. Szucs 1995

18 Membrane permeability rate-limitation seen with polar, hydrophilic compounds (quaternary ammonium compounds, some antibiotics, diuretics) poorly permeable, absorption-limitation lying in the membrane insensitivity to dissolution rate changes, to changes in blood flow Drugs with low oral bioavailability due to poor intestinal permeability Amikacin Cabenicillin Cefamandole Cafazolin Cefotaximine Ceftazidime Gentamicin Neomycin Pyridostigmine Streptomycin Teicoplanin Vancomycin *Less than 20% bioavailable, administered either in solution or as an immediate-release dosage form` 18

19 Gastrointestinal absorption of Ranitidine shows influences or surface area and permeability in various segments of GI tract (naso-enteric intubation): 19 Williams et al., 1992 Thomas D. Szucs

20 Rate-Limiting Steps in Absorption (3): Gastric Emptying hardly any (systemic) absorption from stomach small intestine is main site of absorption in GI tract gastric emptying determines when compound is going to reach site of absorption. compare absorption rates of salicylic acid (pka ~3) from stomach and from intestine (rat) 20 Doluisio et al., 1969 Thomas D. Szucs

21 Gastric Emptying and Absorption Relationship between plasma levels of paracetamol and volume of stomach content voided into intestine 20 mg/kg paracetamol in 400 ml orange juice A without prior treatment B after intra-muscular application of 150 mg pethidin (delaying gastric emptying) Paracetamol Plasma Conc [mg/l] after Pethidin (150 mg i.m.) Time after Intake [min] Gastric Emptying [%] 21 Fricke Thomas 1988 D. Szucs

22 Biopharmaceutical Classification System Based on the properties of Solubility and Permeability, drugs can be classified into 4 categories: High * Solubility Low Solubility High * Permeability Low Permeability Class I e.g. Levofloxacin, Propafenone, Metoprolol Class III e.g. Ramipril, Enalapril, Atenolol, Terbutalin Class II e.g. Glibenclamide, Tolbutamide, Naproxen Carbamazepine Class IV e.g. Piretamide, Furosemide, Hydrochlorothiazide *Highly soluble = if the highest human dose of a drug is soluble in <250 ml water, throughout the physiological ph range. Highly permeable = if the extent of absorption in human is >90% (Jejenum), i.e. it depends on the resistance to mass transport in the intestinal membrane. 22

23 Reasons for Low Bioavailability from Oral Dosage Forms short residence time at site of absorption exposure time of GI mucosa: 1-2 days; shorter at main site of absorption (duodenum: min; jejunum: 3h) time can be too short for poorly permeable drugs (e.g., neomycin; quaternary ammonium salts) or for compounds with limited absorption window (e.g., riboflavin increased F with food) or for drugs with slow dissolution. competing reactions: e.g., chemical, metabolic, efflux first-pass elimination (intestinal wall, liver) 23

24 Distribution 24

25 Fate of Drug After Extravascular Administration: Absorption, Distribution, Elimination Tissue Reservoirs Bound Unbound General Tissue Distribution Site of Action Unbound Bound Target Site Distribution Response Administration Site Absorption Plasma Unbound Drug Renal Elimination Fluids Dose Bound Drug Metabolites Elimination Metabolizing Tissue Biliary Excretion Biotransformation 25 adapted from Benet Thomas et al., 1995 D. Szucs

26 Distribution Extent of Distribution: Distribution Volume Binding to Plasma Proteins and to Tissue Macromolecules Rate of Distribution Distribution and Cp,T-Profiles 26

27 Distribution: Autoradiography Insulin sensitizer compound: Whole body autoradiograms 1.5 and 72 h following oral administration to rats (2 mg/kg) Comment: high levels and retention in adrenal cortex (adc) and liver (lv), high levels in intestine due to biliary elimination

28 Extent of Distribution: Volume of Distribution and the Bathtub Model Concentrat ion = Volume = Dose Volume Dose Concentration 28

29 Binding Proteins for Drugs in Plasma Protein Albumin (4 g/100ml) α 1 -Acid Glycoprotein Lipoproteins Other Transcortin for prednisolone Thyroid Binding Globulin Drugs Acids Bases Specific Drugs Relationship between free and total concentrations: Cu = fu Cp where fu denotes unbound (free) fraction (values from 0 1) 29

30 Determinants for Volume of Distribution: Binding to Plasma Proteins and Tissues, Permeability of Cells from V Cp = V Cp + V C Mass Balance p T T f (protein-drug affinity; protein conc; number binding sites) V = V p + V T fu fu T apparent volume of distribution plasma volume volume of tissue taking up drug Bridge between pharmacokinetics and (patho-)physiology 30

31 Plasma Protein Binding Relationship between Protein binding Magnitude of distribution volume 31 Branch et al., 1976

32 Distribution Parameters Aspects Rate Extent Description (Parameters) t½ for distribution; time to equilibrium volume of distribution; partition coefficients Kp Influencing Factors tissue perfusion rates; ease of tissue permeability; extent of distribution into tissue binding to plasma proteins (free fraction fu) and tissue macromolecules incl. lipids (free fraction fu T ) PK Principles 32

33 Distribution: Summary Small lipophilic molecules show perfusion rate-limited distribution, tissue uptake being directly proportional to capacity and inversely proportional to blood flow. For polar compounds and for certain tissue barriers membrane permeability becomes rate-limiting. The net extent of distribution is indicated by the apparent volume of distribution which is a function of the real volumes of plasma and tissue water and the balance of plasma and tissue drug binding. A physiological conception of volume of distribution allows an understanding and prediction of the effects of disease and drug interactions. 33

34 Metabolism 34

35 Species differences in drug metabolism & toxicity O O Human coumarin Rat HO O O O O 7-Hydroxycoumarin O Coumarin-3,4-epoxide Conjugation and excretion Ring opening to form reactive aldehyde No toxicity Hepatotoxicity 35

36 ADME The role of metabolism (biotransformation) Lipophilic xenobiotic Absorption & Distribution Phase 1 biotransformation Phase 2 biotransformation Hydrophilic metabolite Excretion (urine and feces) Transport (Phase 3) Intestinal and hepatic uptake (OATP) Intestinal/brain efflux (P-gp) Oxidation Reduction Hydrolysis Glucuronidation Sulfation Glutathione conjugation Amino acid conjugation Acetylation, methylation Transport (Phase 3) Introduces or exposes a functional group (OH, NH2, COOH) Conjugation of functional group with water-soluble molecule 36

37 A guide to drug metabolism Xenobiotic with no exposed functional group (OH, SH, NH2, COOH) Xenobiotic with exposed functional group (OH, SH, NH2, COOH) Water-soluble conjugates (excreted in bile or urine) Phase 1 Cytochrome P450 Esterases Phase 2 Conjugation (UGT, SULT, NAT) 37

38 Enzymology of drug metabolism Phase 1 Reaction Enzyme Localization Hydrolysis Carboxylesterase Microsomes, cytosol Peptidase Blood, lysosomes Epoxide Hydrolase Microsomes, cytosol Reduction Azo- and nitro-reduction Microflora, mcs, cytosol Carbonyl reduction Cytosol Disulfide reduction Cytosol Sulfoxide reduction Cytosol Quinone reduction Cytosol, microsomes Reductive dehalogenation Microsomes Dihydropyrimidine dehydrogenase Cytosol 38

39 Enzymology of drug metabolism Phase 1 Reaction Enzyme Localization Oxidation Alcohol dehydrogenase Cytosol Aldehyde dehydrogenase Mitochondria, cytosol Aldehyde oxidase Cytosol Xanthine oxidase Cytosol Monoamine oxidase Mitochondria Diamine oxidase Cytosol Prostaglandin H synthase Microsomes Flavin monooxygenase Microsomes Cytochrome P450 Microsomes 39 Quantitatively, cytochrome P450 is the most important Phase 1 enzyme system

40 Enzymology of drug metabolism Phase 2 Enzyme Cofactor Localization UDP-glucuronosyltransferase (UGT) UDPGA Microsomes Sulfotransferase (SULT) PAPS Cytosol Glutathione S-transferase (GST) GSH Cytosol N-Acetyltransferase (NAT) Acetyl-CoA Cytosol Thiopurine S-methyltransferase (TPMT) SAM Cytosol Glycine and taurine conjugation Cytosol For amino acid conjugation of carboxylic acids, the xenobiotic (R-COOH) is activated by conversion to an acetyl-coa thioester, which is conjugated with glycine, taurine or glutamic acid 40

41 Elimination 41

42 Elimination Clearance a Proportionality Constant Half-life of Elimination PK Principles 42

43 Clearance and the Bathtub Model (1) 43

44 Clearance and the Bathtub Model (2) 44

45 Elimination Parameters Aspects Description (Parameters) Influencing Factors Capacity Clearance (CL) Liver high E 1) low E Kidney lipophilicity, membrane permeability; availability of drug at enzymes; affinity to enzymes; amount of enzymes Q fu, CL int ( V max ) Km creatinine clearance, fu (filtration); polarity, ionization (reabsorption); secretory mechanisms (secretion) Rate t1/2 Clearance; volume of distribution 1) E = Extraction ratio = CL h,b Q h 45

46 Half-Life, a Secondary Parameter t1/ 2 ln2 V = CL independent variables dependent variable note use of (elimination) of half-life: length of permissible max dosing interval (ought to be based on conc-effect relationship!) 46

47 Biological Half-Lives of Elimination for Some Drugs in Adults Nitrofurantoin Methicilline Oxacilline Benzylpenicilline Cloxacilline Furosemide PAS Ampicilline Carbenicilline Rifampicine Heparin Gentamycin Paracetamol Pentazocine Lidocaine Propoxyphene Morphine Isoniazid Acetylsalycilic acid Phenacetin Diuretics of benzothiadiazine type 0.3 h 0.5 h 0.5 h 0.5 h 0.5 h h 1 h 1.5 h 1.5 h 1.5h 1.5h 2 h 2 h 2 h h h 2-3 h 2-4 h 2-4 h 3 h 3 h Propranolol Imipramine Procainamide Methyldopa Tetracycline Tolbutamide Ethambutol Doxycycline Meprobamate Minocycline Phenytoine Amphotericin B Chlordiazepoxide Chlorpropamide Phenobarbital Chlorochin chloroquine Phenylbutazone Lithiumcarbonate Guanethidine Diazepam (metabolite) Reserpine (metabolite) 3.2 h 3.5 h h 3-12 h 6-8 h 7 h 6-8 h 8 h 8 h 8 h 13 h h h h h 48 h 72 h 1-2 d 2-3 d 2-10 h 2-8 d 4.5 h d 47

48 Accumulation after Multiple Oral Dosing (1) Drug with t 1/2 6 hours Dose 100 mg Case 1: τ 24h Case 2: τ 6h Menge (mg) Zeit tau1 = 24h tau2 = 6h 48

49 PK in Drug Development 49

50 Non-Clinical DMPK Studies in Drug Development (1) Drug Selection: Issues Tools Absorbability Metabolic stability Interaction potential Tissue penetration physicochemical models - lipophilicity - molecular size, shape - surface charge cellular / tissue models - Caco-2-cells monolayer - dialysis in Ussing chamber in situ models - perfused isolated intestine in vivo models microsomes, hepatocytes, organ slices microsomes, hepatocytes, isolated transporters cell cultures, in vivo experiments, autoradiography

51 Non-Clinical DMPK Studies in Drug Development (2) BEFORE Entry-into-man Objective: Show safety of new drug (to us, to Ethics Committee, to Authorities) Issues DMPK input into design/interpretation of tox studies what non-rodent species? similarity of metabolic pattern animal-man increasing exposure with increasing dose large exposure span what observation-time points for exposure assessment? what analytes? activity of metabolites what formulations reproducibility of drug delivery, variability highest possible absorption Tools metabolic profiles in vitro and in vivo whole animal studies PK in possible tox species PBPK modeling metabolic studies, structure identifications formulation screen in animals 51

52 Non-Clinical DMPK Studies in Drug Development (3) BEFORE Entry-into-man Objective: Show safety of new drug (to us, to Ethics Committee, to Authorities) Issues Safety margin conc-based measure of exposure in tox studies comparative protein binding Complete recovery of administered dose Target tissues for drug accumulation Mechanistic information on absorption and disposition Tools toxicokinetics safety margin calculated for free drug mass balance in vivo tissue distribution, autoradiography cellular, tissue, whole animal models PBPK modeling Extrapolation across species elimination routes, clearance mechanisms 52 allometry PBPK modeling

53 Non-Clinical DMPK Studies in Drug Development (4) BEFORE Entry-into-man Objective: Prepare for the first human trial Issues Dosing issues Starting dose safety of lowest dose avoid unnecessary dosing steps Dosing increments linear relationship between dose and conc? Population Importance of polymorphic enzymes Variability absorption mechanism involved isozymes in metabolism Tools interspecies extrapolations incl. allometry, PBPK or PKPD modeling metabolizing enzymes identification involvement of transporters 53

54 Non-Clinical DMPK Studies in Drug Development (5) AFTER Entry-into-man Objective Prepare for (sub-)chronic use of drug Support line extension Analytics of human samples Issues Human metabolism, mass balance - Interspecies comparison DMPK input into design/interpretation of tox studies DMPK in additional species conc-based measure of exposure in long-term tox studies Mechanistic explanation for unusual observations (see bosentan, posicor, ) Broaden experience with drug in variety of situations chronic use (indication) perinatal disease models Formulation support, bioavailability Prediction of interactions (absorption, elimination) Formulations, indications, route of administration Develop method for additional analytes Adjust method to various situations (sensitivity, polypharmacy, ) 54

55 Sources of variation in ADME Interindividual differences Genetic (inherited) Environmental Background Polymorphisms Lifestyle Disease Age Maturity Gender Ethnicity CYP enzymes FMO3, UGT s Methyltransferase Transporters PM versus EM Smoking Alcohol Food Herbals Nutraceuticals OCS Liver disease Kidney disease Infection Inflammation Drug interactions 55

56 Sources of variation in ADME Genetic polymorphisms in CYP enzymes Enzyme Incidence Victim drugs CYP2D6 ~7% Caucasians Debrisoquine Sparteine Perhexilline CYP2C19 ~20% Asians Omeprazole Lansoprazole CYP2C9 1-5% Warfarin Not approved by FDA due to adverse events in PMs Efficacy in PMs > efficacy in EMs Dosage may need to be increased in EM s Narrow therapeutic index. Therapeutic monitoring required. Dosage is reduced In CYP2C9 PMs to achieve anticoagulation without risking hemorrhage NB: The incidence of the PM phenotype varies 56 from one ethnic group to the next

57 Sources of variation in ADME Genetic polymorphisms in PK enzymes Polymorphism CYP2D6 CYP2C8 CYP2C9 CYP2C19 CYP3A5 (and P-gp) UGT1A1 TPMT DPDH FMO3 P-glycoprotein (ABCC1) OATP-1B1 Victim drug Numerous Repaglinide Warfarin Proton pump inhibitors (e.g., omeprazole) Tacrolimus in pediatric patients Irinotecan, morphine, tolcapone 6-Mercaptopurine 5-Fluorouracil Many + trimethylamine Digoxin Pravastatin The conversion of codeine to morphine and, hence, the analgesic effect of codeine are impaired in CYP2D6 PM s The trimethylaminuria associated with FMO3 deficiency goes by the unfortunate name of fish-odor syndrome 57

58 Victims (objects) versus Perpetrators (precipitants) Victims Clearance determined by a single route of elimination Victim drugs Not approved Debrisoquine, perhexilline Victim drugs Withdrawn Terfenadine, cisapride, astemizole and cerivastatin Victim drugs Loss of efficacy Oral contraceptive steroids, HIV and immunosuppressive drugs Perpetrators Factors that alter the clearance of a victim drug Genetic polymorphisms CYP2D6 (PMs and EMs) Inhibitory drugs Erythromycin, ketoconazole Mibefradil (withdrawn) Inducing drugs Rifampin, EIAEDs, (SJW) None withdrawn, but may be denied approval (AIDS patients) Victim drugs with a large therapeutic index are approved by 58 the FDA (e.g., Lilly s Strattera, which is cleared by CYP2D6)

59 The ideal drug Everyone responds with no ADE Response or frequency Therapeutic effect UM EM IM PM Adverse effect AUC or Css Large therapeutic index - No dosage adjustment required for UMs or PMs 59

60 A victim drug A population (UMs or PMs) is at risk Response or frequency Therapeutic effect UM EM IM PM Adverse effect UMs can be created with CYP inducers, and PMs can be created with CYP inhibitors AUC or Css Narrow therapeutic index - Dosage adjustment required for UMs or PMs 60

61 Market withdrawal of victim drugs and perpetrators Victim drugs withdrawn from the US market Seldane (terfenadine) Propulsid (cisapride) Hismanal (astemizole) Baycol (cerivastatin) Perpetrator drugs withdrawn from the US market Posicor (mibefradil) Extensively metabolized by CYP3A4 Cause ventricular arrhythmias (Torsades de Pointes) when coadministered with a CYP3A4 inhibitor (e.g., erythromycin, ketoconazole) CYP2C8 & OATP substrate. Causes rhabdomyolysis with gemfibrozil or clopidogrel Calcium channel blocker (antihypertensive) Metabolism-dependent inhibitor of CYP3A4 Causes extensive and prolonged inhibition of CYP3A4, which resulted in numerous DDI 61

62 Pharmacokinetic Principles: What have we learnt? what the processes are determining Cp,Tprofiles how we can describe and quantify absorption, distribution, elimination what we have to do to bring them under our control what the meaning of pharmacokinetic parameters is and how they are determined 62

63 From Active Drug Substance to Pharmacodynamic Effect Active Compound Drug Formulation Plasma Concentration Duration and Intensity of Effect Dose Excipients Processes Disintegration Dissolution Absorption Distribution Metabolism Excretion Binding Receptor Sensitivity in vitro in vivo Pharmacy Galenics Pharmacokinetics Biopharmaceutics Pharmacology Medicine PK Principles