Drug Disposition and the Fate of Drugs

1. Drug Disposition and the Fate of Drugs 19th September 2012 Colin Vose VP, Strategic Drug Development Centre for Integrated Drug Development Quintiles Ltd

2. Objectives • The importance of pharmacokinetics • Brief revision of pharmacokinetics and pharmacodynamics • Animal ADME in drug development • Clinical pharmacokinetics in drug development

3. R and D attrition: DMPK challenge Safety ADRs Efficacy Prentis 1988 B J Clin Pharm, 25, 387-396 Other DMPK (7% excluding anti-infectives) Kennedy, T. 1997, DDT 2: 436-444

4. Critical PK/ADME Questions 1 • How much of the drug is absorbed, how much reaches the systemic circulation and how quickly (absorption/bioavailability)? • Does the drug reach the site of action andwhat organs are exposed to the drug and/or metabolites (distribution)? • How long does it stay in the body, how is it removed and are there any active metabolites (elimination)? • Are the pharmacokinetics of the drug linear with dose and time? • What factors affect drug disposition? • What are the most appropriate route(s) and means of administration? • Are these characteristics consistent with the clinical and commercial objectives?

5. Critical PK/ADME Questions 2 • What are the appropriate doses/dosage regimens for: • Animal pharmacology/toxicology? • Healthy volunteers? • Patients….general, sub-groups, individuals? • Which drug interactions are likely to be important determinants of clinical acceptability and use: • Caused by the new drug? • Exerted on the new drug? • Why have you adopted the development strategy? • What are the key features determining the understanding of how this drug is handled by the body? • Do you fully understand the relationship between the formulation/absorption/disposition and the desired/adverse affects?

6. Pharmacokinetics and Pharmacodynamics • Pharmacokinetics (PK): The time course and movement of drugs in the body i.e. what the body does to the drug • Absorption • Distribution • Metabolism • Excretion • Pharmacodynamics (PD): The time course and intensity of drug action in the body i.e. what the drug does to the body, includes wanted and unwanted effects • Pharmacology • Toxicology • Adverse events/side effects • There is a relationship between PK and PD } Elimination

7. PK: Intravenous drug concentration-time profile 1500 AUC∞ = AUC0-t + Ct/λz 1200 Plasma concentrattion (ng/ml) Cltot= Dose AUC∞ 900 600 300 10 30 50 70 90 110 Time (min)

8. PK: A semi-logarithmic plasma concentration-time plot C0 1500 Cp = C0e-λt 750 T1/2 = 0.693 VD 375 Cltot Plasma concentration 187.5 λ Time (min) 10 30 50 70 90 110 130 150 T1/2

9. PK: Multi-exponential i.v. plasma concentration-time curve 1000 C1 500 Cp= C1e-λ1t + C2e-λ2t A F C2 100 B G 50 Plasma concentration (ng/ml) F = A - W G = B - X H = C - Y I = D - Z C D W Y X 10 Z H λ2 5 λ1 I 1 0 4 8 12 16 Time (h)

10. PK: Time Course Of Orally Administered Drug Cmax ;tmax Toxic C F= AUC(po) x Dose(iv) AUC(iv) x Dose(po) Therapeutic E Plasmalevel B D A F Ineffective Time Cp= C1e-λ1t+ C2e-λ2t - C3eλ3t

11. Time (h) Single oral dose PK profiles in man 500mg Concentration (ng/ml) 250mg 125mg

12. Dose linearity of pharmacokinetics Cltot = F xDose AUC∞ AUC∞ μg.h/ml Dose mg

13. PK and PD Objectives At steady-state Rate in = Rate out = CltotxCss Time to steady-state is ~ 4 t1/2 Toxic Plasma level Css Effective Ineffective Time

14. Pharmacodynamics • Based on: • Dose or concentration/response curves • Log dose/response curves • Log concentration/response curves • Emax model • Concentration/Emax model

15. Pharmacodynamics Drug Receptor Interaction Drug (D) + Receptor (R)DR Effect Michaelis-Menten Equation: Maximal Effect(Emax) . C Effect = KD + C Where KD = dissociation constant or IC50 C = Free Drug Concentration

16. Parameters from E max curves – cartesian Effect (E) Emax E0 Free Drug Conc Effect (E) e.g. HR, BP, %Enzyme inhibition

17. PK/PD Modelling Emax· CN E = + E0 EC50N+ CN Where: E is the effect measured; E0 at zero time; Emaxmaximal effect C is the concentration producing the effect N is the slope of the log conc/response curve Efficacy will increase faster with concentration at greater N values

18. Parameters from Emax curves - effect of slope (N) Effect (E) 2 1 E MAX 0.5 Eo EC50 Log Free Drug Conc Effect (E) e.g. HR, BP, %Enzyme inhibition

19. Relationship between Dose/PK/PD for tertatolol Increase in heart rate (%) 1 mg 2 mg 5 mg 10mg N = 0.5 10 100 1000 1 Log Plasma Cpu (ng/ml) Poor correlation between dose and effect, good correlation between plasma free drug concentration (exposure) and effect

20. Pharmacology/Toxicology: Log concentration vs response curves anaesthesia respiratory depression convulsions - acute Intensity of Effects liver failure - chronic Log plasma concentration Based on knowledge of preclinical and clinical PK/PD predict exposure/response relationships and monitor accordingly

21. Influence of Physicochemical Properties on Drug Disposition

22. Elimination pathways • Excretion of drug and/or metabolites in urine, bile and/or faeces • Metabolism of the drug and/or primary metabolite(s) • Phase I reactions produce or introduce a new chemical group in a drug molecule • Oxidation • Reduction • Hydrolysis • Phase II or conjugation reactions involve the linking of the drug to an endogenous molecule • Glucuronidation • Sulphation • Amino acid/glutathione • N-acetylation

23. Drug Metabolism and Pharmacokinetic Techniques • In vitro • Microsomes: rat, dog, monkey, human • Isolated expressed cytochromes, tissue homogenates, • Primary hepatocytes • Cell cultures, tissue slices, isolated perfused organ(s) • In vivo • Whole animal: rat, dog, monkey, human • Bioanalytical techniques • LC-MS, LC-MS/MS, HPLC-UV, immunoassay • LC-NMR, LC-MS • Radioisotope Techniques

24. When & What for Preclinical Pharmacokinetics When Which What Why Drug Discovery Rat/mouse/dog/ (monkey)/man In vitro PK/ADME in cell Caco-2 cells/ microsomes/hepatocytes Absorption potential metabolism rates, routes, enzymes Clearance, t1/2, abs/ bioavailability Drug Selection Rat/dog/(monkey) In vivo plasma PK po/iv Plasma/tissue concentrations Pharmacology Rat/ mouse/ guinea pig/ dog Establish PK/PD relationships PK exposure Tissue distribution Excretion balance Elimination routes Enterohepatic circulation Milk and placental transfer Species validation Toxicokinetics 14C-ADME Metabolite profiles/identification Rat/mouse/dog/rabbit/ (monkey) Toxicology Reprotoxicology Long Term carcinogenicity Rat, dog, mouse Exposure, AUC Toxicokinetics

25. Relevance of drug metabolism to drug action DrugMetabolite Pharmacologically activeInert Toxic Pharmacologically active Inert (Prodrug) Toxic • Relating pharmacodynamics to the fate of the drug • Interspecies comparison to support interpretation of pharmacology and toxicology • Drug design • Lead optimisation

26. Drug Metabolism • What are the metabolic pathways? • Which enzymes systems are involved? • Is a genetic polymorphism involved? • Is the drug an inducer or inhibitor? • What are the possible drug interactions?

27. CYP450 Nomenclature Ancestral gene (140mya) superfamily of haem-thiolate enzymes CYP 1 2 3 4 = 40% family 2A 2B 2C 2D 2E = >55% subfamily 2A1 2A2 2A3 2A6 =individual genes Nebert et al., 1989

28. CYP Compounds Hepatic Level (%) Inhibition Induction Polymorphism 1A 1/2 Caffeine Biphenols 13   (smoking) (ethnic groups) 2A Coumarin 4   2C9/19 Tolbutamide Phenytoin 18   5%Cauc 23% Oriental 2D6 β-blockers Antidepressants 2  -  5-10% Cauc 2E1 p-Nitrophenol Paracetamol 7   (ethanol)  3A4 Many compounds 30  (grapefruit)  Variability (X80) Information for specific CYP-450 isozymes 

29. Which CYP-450 metabolises my drug? • Incubate drug with microsomes alone and with compounds • that specifically inhibit particular CYPs

30. Genetic Differences N N NH NH C C NH2 NH2 4-Hydroxy-debrisoquine Debrisoquine • Genetic polymorphism(s) • 5 - 10% of Caucasians lack the CYP2D6 gene controlling the hydroxylation (poor metaboliser = PMs) • Individuals on anti-epileptics behave as PMs due to DDI

31. Drug Example Safety Issue/Concern Debrisoquine Postural hypotension & physical collapse Sparteine Oxytoxic effects Perphenazine Extrapyramidal symptoms Flecainide Pro-arrythmic effects Perhexiline Peripheral neuropathy & hepatotoxicity Phenformin Lactic acidosis Propafenone CNS toxicity Metoprolol Loss of cardioselectivity Nortriptyline Hypotension & confusion Ecstacy Death Side Effects Related to CYP-450 2D6 Polymorphism

32. CYP-450 Inhibition • Determine ability of drug to interfere with metabolic clearance of other drugs • Incubate drug with specific substrates of CYPs e.g. CYP-450 Isoform 1A2 2A6 2C9 2C19 2D6 2E1 3A4 Marker Substrate Phenacetin O-Deethylation Coumarin Hydroxylation Tolbutamide Hydroxylation S-Mephenytoin Hydroxylation DextromethorphanDemethylation Chlorzoxazone Hydroxylation Testosterone 6ß-Hydroxylation

34. Rate of Metabolism (Clint) Vmax Rate ½Vmax Rate= Vmax * S Km + S Km Substrate Concentration In vitroCLint = Vmax/Km at low [µM] In Vivo Cl = Fu.Clint.Qh Fu.Clint + Qh

35. Predicting human clearance by in vitro-in vivo scaling

36. Dose scaling - Allometry 1000 100 10 1 0.1 1.0 10.0 100.0 BW (kg)

37. Prediction of human clearance by allometry Passive renal filtration, logD7.4< 0 High first pass Cl, low F

38. Factors affecting drug disposition

39. Effect of Dose Level HNCOCH3 Paracetamol (analgesic) OH Therapeutic Dose Reactive Products Glucuronide and Sulphate Conjugates Overdose Glutathione React with Macromolecules Mercapturate Hepatotoxicity

40. Effect of Age Imipramine PK parameters Vd and fu unchanged: Decrease in clearance is due to reduced ability of the ‘aged’ liver to N-dealkylate

41. Effect of Disease • Hepatic disease: • Propranolol (high first pass) has increased bioavailability in patients with liver disease ( ClH) • Decreased metabolism  Increased exposure • Kidney disease: • Renal clearance (ClR) • Decreased excretion  Increased hepatic clearance and exposure

42. Effects of Food and Drug Interactions • Food effects: • No effect • Modify absorption/bioavailability e.g. spironolactone (increase); propentophylline (decrease) • Metabolic Inhibition: • Decrease in clearance ( t1/2) • Cimetidine on diazepam, terfenadine (3A4) • Grapefruit juice inhibits CYP3A4:  F % of omeprazole (Losec) • Metabolic Induction: • Increase in clearance ( t1/2) • Carbamazepine, phenytoin, barbiturates, alcohol (CYP3A4) • Cigarettes, BBQ (CYP1A2)

43. Implications of Terfenadine-Ketoconazole Interaction CYP3A4 Terfenadine Almost complete first pass extraction in man Active metabolite Responsible for efficacy in man Inhibited by Ketoconazole High circulating concentrations of terfenadine prolong QT interval of the ECG Abnormal heart rhythm Small numbers of patients go on to develop fatal Torsade de Pointes Terfenadine withdrawn from the market Increased questioning of Regulatory Authorities on QT and DDIs

44. Interaction Studies • Identify metabolising isozyme & potential interacting drugs • In vitro human liver microsomes with/without known CYP-450 inhibitors/inducers • Specific studies for potential co-administered drugs • Selected based on risk indicated by in vitro studies • Food effects on absorption (Phase I) • Pharmacokinetic screen (Population Approach in Phase II and III)

45. When and what for clinical pharmacokinetics and pharmacodynamics

46. Use of preclinical and Phase I/IIa data, to support Go/No Go decisions?

47. Summary • Pharmacokinetics & metabolism studies are used throughout drug R and D • They are the bridge between: • Dose & effect • Animals & man • Healthy volunteers & patients • Pharmacokinetics is a surrogate measure for pharmacodynamic effects and is of most value when PK/PD relationships are established • Pharmacokinetic data allows • Prediction of dose regimen, interactions, dose adjustment in disease • Quantify effect of food, gender, age, race

48. Summary (contd.) • Identification of metabolic enzymes may allow prediction of: • Induction • Inhibition • Variability • Drug interactions • This information is essential for the: • Product license to market • Information to patients (data sheet) • Market positioning

49. References/reading list • R. M. J. Ings, in “Medicinal Chemistry Principles and Practice” ed. F. D. King, Royal Society of Chemistry, Cambridge, 1994, pp 67-85. • C. W. Vose, in “Medicinal Chemistry Principles and Practice” ed. F. D. King, Royal Society of Chemistry, Cambridge, 1994, pp 86-97. • G. G. Gibson and P. Skett, “Introduction to Drug Metabolism”, Nelson and Thomas, 2001. • M. Rowland and T. Tozer, “Clinical Pharmacokinetics. Concepts and Applications”, Lea and Febiger, Malvern, Pennsylvania 1989 (and subsequent revisions). • M. Gibaldi, “Biopharmaceutics and Clinical Pharmacokinetics - Fourth Edition”, Lea and Febiger, Malvern, Pennsylvania 1991. • Drug Metabolism - from Molecules to Man, ed. D. J. Benford, J. W. Bridges and G. G. Gibson, 1987 (good general background to subject)