Biopharmaceutics PDF

MODULE 4│PHARM 4 BIOPHARMACEUTICS BIOPHARMACEUTICS Biopharmaceutics involves factors that influence: Bio – life...

MODULE 4│PHARM 4 BIOPHARMACEUTICS BIOPHARMACEUTICS Biopharmaceutics involves factors that influence: Bio – life 1. The design of the drug product. Pharmaceutics – General area of study concerned with the 2. Stability of the drug within the drug product. formulation, manufacture, stability and effectiveness of 3. The manufacture of the drug product. pharmaceutical dosage forms. 4. The release of the drug from the product. Examines the interrelationship of the physical/ chemical 5. The rate of dissolution/ release of the drug at the absorption properties of the drug, the dosage form (drug product) in site. which the drug is given, and the route of administration on 6. Delivery of drug to the site of action which may involve the rate and extent of systemic drug absorption. targeting a localized area for action or systemic absorption of drug. INTRODUCTION PHARMACODYNAMICS DRUGS Refers to the relationship between the drug concentration at These are substances intended for use in the diagnosis, the site of action (receptor) and pharmacologic response, cure, mitigation, treatment or prevention of disease. including biochemical and physiologic effects that influence Drugs are given in a variety of dosage forms or drug the interaction of drug with the receptor. products such as solids (tablets, capsules), semisolid, What the drug does to the body liquids, suspensions, emulsion, etc., for systemic or local activity. Toxicokinetic Drug product can be considered to be drug delivery systems Application of pharmacokinetic principles to the design, that release and deliver drug to the site of action that they conduct and interpretation of drug safety evaluation studies produce the desired therapeutic effect and are also designed and in validating dose-related exposure in animals. specifically to meet the patient’s needs including palatability, convenience and safety. Clinical Toxicology The study of adverse effects of drugs and toxic substances Drug Product Performance (poisons) in the body. The release of drug substance from the drug product either for local drug action or for drug absorption into the plasma for PHARMACOKINETICS systemic therapeutic activity. The release of the drug substance from the drug product Is the science of the kinetics of drug absorption, distribution leading to bioavailability of the drug substance and and elimination (metabolism and excretion) eventually leading to one or more pharmacologic effect. PRINCIPLES OF PHARMACODYNAMICS BIOAVAILABILITY Pharmacodynamics – “What the drug does to the body” Refers to the measurement of the rate and extent of active Study of the biochemical and physiologic effects of drugs in drug that reaches the systemic circulation. biological systems, means access to the bloodstream Study of the mechanism by which these effects are produced → Mechanism of Drug Action (MOA) Sequence of events A. PHARMACODYNAMICS: MECHANISM OF DRUG ACTION Absorption 1. Receptor-mediated Receptor – cellular macromolecule, or an assembly of Drug release and Drug in systemic Dissolution circulation Drug in tissues macromolecules, that is concerned directly and specifically in chemical signaling between and within cells 2. Non-Receptor-mediated Examples: Elimination Direct chemical interaction – acid neutralizers (antacids), chelating agents (drugs that coat and coat bind to heavy metals that are present in excessive Excretion and Pharmacologic amount in the body) Metabolism clinical effect Colligative mechanism (dependent on the particles of Critical Manufacturing Variables the drug in solution)/ mass effect – osmotic diuretics The most important steps in manufacturing process. Counterfeit incorporation – purine-pyrimidine analogues Biopharmaceutical Consideration in Drug Product Design RECEPTOR LOCATIONS Cell membrane Items Considerations Cytoplasm Therapeutic Drug is intended for rapid relief of symptoms, Nucleus Objectives slow extended action given per day (weeks or longer), or chronic; is the drug for local action or systemic action Drug (API) Physical chemical properties of API, including solubility, polymorphic form, particle size Route of Oral, topical, Parenteral, transdermal, Administration inhalation, etc. Drug Dosage and Large or small drug dose, frequency of doses, dosage regimen patient acceptance of drug product, patient compliance Type of Drug product Orally disintegrating tablets, immediate release tablets, transdermal, parenteral, implant, etc. Method of Variables in manufacturing process, including Manufacture weighing, blending, release testing, sterility Module 4 – Biopharmaceutics Page 1 of 8 RJAV 2022  Cell membrane Voltage-gated Na+ channel – blocked by Class I GPCRs antiarrhythmics, local anesthetic, tetrodotoxin, saxitoxin Ion Channels Voltage-gated K+ channel – blocked by Class III Kinases antiarrhythmics such as Amiodarone and Sotalol Catalytic receptors Voltage-gated Ca2+ channels – blocked by CCBs such as Enzymes Verapamil, Diltiazem, Amlodipine. Transporters Structural protein and other molecules b. Ligand-gated Cytoplasm and Nucleus Structural protein and other molecules Thyroid hormone receptor Steroid receptors *Gating mechanism is controlled by a certain binding site, particularly a ligand RECEPTORS may be able to interact. So, if a ligand interacts at the binding site, it will cause a change in configuration of the gate causing the gate to open and that will 1. GPCR (G protein-coupled receptor) now allow the movement of certain molecules or ions 7-transmembrane spanning receptor Nicotinic receptor (Na+) Channel) – blocked by Metabotropic – effects due to metabolites (or 2nd neuromuscular blockers derived from tubocurarine messengers) GABAA receptors (Cl- channel) – stimulated by BZDs, Involved in signal transduction Barbs Most common receptor 3. Kinases and Catalytic Receptors * The cell membrane and the GPCR consist of molecule that reverses the entire span of the cell membrane 7 times so that’s the reason we call it 7- transmembrane spanning receptor. Now intracellularly, this receptor is associated with the G-Protein it is called G-Protein because this protein is intimately link to GDP. When a Drug or a Ligand bind to receptor the GDP is replaced by GTP and once this happens it will lead to production of 2nd messengers. If on the other hand the G-protein is not activated meaning the GDP is not replaced by GTP then what we expect would be a decrease in the 2nd messengers. This process where a drug binding to receptor that is found at *Are characterized by receptors that exist as monomers. What happens with the cell membrane which leads to stimulation of intracellular protein like the G- the monomers is that when the ligand interacts with the monomers, they protein is what we refer to as a Signal transduction process. dimerize and this dimerization of receptors will lead to the activation of the receptors. There are several types of Kinases and Catalytic Receptors, and this type will depend on whether the kinase is an integral component or part of Types of GPCR: the entire receptor molecule or is a separate molecule from the receptor molecule. Gs Activation of AC (Adenylyl cyclase) ✓ Increase in cAMP ✓ Ex: Beta-receptors *It will activate the enzyme called Adenylyl cyclase this enzyme coverts ATP to the active cAMP intracellularly. cAMP inside the cell is metabolized by the enzyme Phosphodiesterase III which converts it to the inactive AMP. Gi Inhibition of AC (Adenylyl cyclase) ✓ Decrease in cAMP → inhibitory 4. Enzymes ✓ Ex: alpha 2 presynaptic receptors ACE (Angiotensin Converting Enzyme) or Kininase II – Gq responsible for converting Angiotensin I to the more active Activates PLC (Phospholipase C) – acts in triglycerides Angiotensin II (responsible for vasoconstricting effect and drug such ✓ Splits PIP2 → IP3 + DAG (2nd messengers; primarily as: Captopril, Enalapril, Lisinopril can inhibit the activity of involved in smooth muscles activities, so they increase Angiotensin Converting Enzyme this class of drugs are called ACEi) intracellular calcium level in smooth muscles and are involved in COX (Cyclooxygenase): inhibit by NSAIDS the phosphorylation and activation of the myosin light chain MAO: inhibited by MAO-Is kinase) Non-specific: Tranylcypromine, Isocarboxazid, ✓ Ex: alpha postsynaptic receptors Phenelzine ✓ Location: smooth muscles → contraction MAOA: Moclobemide (RIMA) MAOB: Selegiline, Rasagiline, Safinamide 2. Ion channels 5. Transporters a. Voltage-gated *Cell membrane and examples of Ion channel at the end, you see a gating mechanism that prevents ions from moving in or out through the channel. A voltage-gated ion channel is primarily governed by a change in the membrane The characteristics of a transporter or carrier molecule, is that it brings ions potential. So, at resting state we know that the inside of the membrane is more into or out of the cell by changing its confirmation or configuration. In the case negative than the outside if there is a change however in the membrane of Na+-K+ ATPase it brings out 3 Sodium ions as it brings in 2 Potassium ions, potential such as the inside becomes less negative or even positive there will the movement of this carrier requires energy or ATP. now be a change in configuration of the gate which prevents the movement of ions through the channel and may lead to opening of the gate. Module 4 – Biopharmaceutics Page 2 of 8 RJAV 2022 Examples: Types: GPCRs, Ion channels, Transporters, Enzymes, Na+-K+ ATPase: inhibited by Digitalis (Digoxin) Structural proteins, nuclear receptors Proton Pump (H+-K+ ATPase): inhibited by PPIs (Omeprazole) B. PHARMACODYNAMICS: CHARACTERISTIC OF DRUG- RECEPTOR INTERACTION 6. Structural Proteins and other molecules Definitions: Affinity Ability to bind to a receptor or target protein Ligand-activity Intrinsic activity Ability to generate a series of biochemical events leading to an effect after receptor-binding Constitutional activity Ability to generate a series of biochemical events leading to receptor effects even in the absence of a ligand Receptor Binding Sites: Orthosteric site Primary binding site Allosteric site. Allosteric site Binding site of other molecules Microtubule consists of Dimers (α-tubulin and β tubulin), these dimers can Can alter binding of endogenous ligand to the orthosteric site be added to the chain or they can be removed from the chain. So, when additional dimers are added in to the chain, we called it polymerization and Agonists, Inverse Agonists, Antagonists there is lengthening of the microtubule, in contrast when dimers are removed from the chain, we called it depolymerization and there is shortening of the microtubule. Microtubules: Cytoskeleton Organelle movement From mitotic spindles Agonists Stabilizes active receptor state Inverse Agonist Stabilizes inactive receptor site Inhibitors: Griseofulvin Antagonist Colchicine Maintains equilibrium Anti-mitotics – Taxanes, Vincas, Estramustine, Epothilones between the inactive (Ixabepilone) and active receptor states 7. Nuclear Receptor – are found initially at the Cytoplasm and when Prevents binding of the ligand is bound to them, they form a complex and they are then agonist translocated into the nucleus Allosteric modulators: Thyroid hormone receptors Allosteric agonists Steroid receptors Improve/ enhance binding of endogenous ligand to the orthosteric site MOA: Allosteric antagonists Reduce or prevent binding of endogenous ligand to the orthosteric site Agonists: Full agonists Produce the maximal clinical effects expected with receptor interaction Partial agonists Produce less than the maximal clinical effects expected with receptor interaction. Summary: Produce some of the anticipated effects with receptor interaction and inhibit other effects attributed to receptor Two General MOAs: Receptor-mediated and non-receptor- interaction (Mixed agonist-antagonist activity) mediated Antagonists: Non-receptor-mediated: direct chemical interaction, Clinical antagonist colligative mechanism, counterfeit incorporation Drugs that produce clinical effects that are opposite of Receptor-mediated: another drug or of the endogenous agonist Cell membrane, cytoplasmic, nuclear Includes Antagonists and Inverse agonists Module 4 – Biopharmaceutics Page 3 of 8 RJAV 2022 Classification of Antagonists: a. Based on Mechanism of antagonist action Pharmacologic opposite effects produced by binding to the same receptor or receptor system Example: Stress or Anxiety Due to Epinephrine/ Adrenaline Increase HR by binding to β1 Tremors due to binding to β2 Hill-Langmuir Equation Treatment: Propranolol 𝐾 Decreases HR by binding to β1 𝐴 + 𝑅 ⇄ [𝐴 − 𝑅] Reduces tremors by binding to β2 Where: A: agonist or ligand Physiologic R: receptor Produce opposite effects by binding to a different receptor [A-R]: agonist-receptor complex K: equilibrium dissociation constant Example: Anaphylactic shock pAR: proportion of binding sites occupied by ligand at equilibrium Due to massive Histamine release Vasodilation/ Hypotension by binding to H1 receptors Affinity Bronchospasm by binding to H1 receptors [𝐴 − 𝑅] [𝐴] 𝑝𝐴𝑅 = = Treatment: Epinephrine 𝑅 + [𝐴 − 𝑅] [𝐴] + 𝐾 Vasoconstriction by binning to α1 receptors Bronchodilation by binding to β2 receptors b. Based on ability to surmount antagonist/ opposite effect Guide question: Dose-Response Graphs Can the effect of the “antagonist” be completely overcome by increasing the dose or concentration of the “agonists”? 1. Graded Dose-Response Graph YES (completely) – Competitive antagonist NO (or incompletely) – Non-competitive antagonist Plot of Response against Dose or Log Dose Example: Drug A decreases SBP from 160mmHg to 120mmHg at 10mg/day. Dug B is taken by the patient at 500mg dose causing the SBP to increase to 160mmHg. You advise to increase the dose of Drug A to 15mg/day which caused the SBP to drop again to 120mmHg. Did the increase in the dose of Drug A completely overcome the effect of Drug B? YES. So, Drug B is a competitive antagonist of Drug A Parameters: c. Based on reversibility of drug-receptor interaction a. Efficacy: maximum achievable response Ceiling effect D + R → [D-R] or D + R ⇄ [D-R] b. Ceiling Dose (DC): smallest dose that produces the maximum response Reversibility is dependent on the Type of bond/ Interaction formed c. Potency (P): dose producing 50% of the maximum between the Drug and Receptor response Reversible: interaction involves IMFAs (intermolecular forces of d. Mid-slope: degree of change in response with change in attraction) dose H-bond, vDW forces of attraction, dipole interaction, London forces, etc. Irreversible: interaction involves a permanent bond Covalent bond Clinical clue: duration of action Duration of action < 24 hours – likely reversible Propranolol lowering of HR 24 hours – likely irreversible Antiplatelet effect of aspirin lasting for about 7 – 10 days after stopping therapy C. PHARMACODYNAMICS: DOSE RESPONSE RELATIONSHIP Relationship between concentration/ dose and effect Hill Equation: 𝐸 [𝐴]𝑛𝐻 = 𝐸𝑚𝑎𝑥 [𝐴]𝑛𝐻 + [𝐴]50 𝑙𝑛𝐻 Where: E: Effect Emax: Maximum Effect [A]: concentration of the agonist [A]50: concentration of agonist producing half maximal effect nH: Hill coefficient (slope of a logarithmically transformed binding curve Module 4 – Biopharmaceutics Page 4 of 8 RJAV 2022  Mid-slope Steep slope: small increase in dose leads to a large change in response “Toxicity” Necessities to “start LOW, go SLOW” Applications Differentiate Potency and Efficacy Efficacy: A = C >> B Potency: A > B > C Non-competitive antagonism: Shift pf the graph down and to the right 2. Quantal Dose-Response Graph Plot of cumulative number of Responders against the Dose A more effective drug is NOT necessarily more potent A more potent drug is NOT necessarily more effective Differentiate Partial agonist from Full agonists Parameters: a. ED50: median effective dose b. TD50: median toxic dose c. Therapeutic index (I) = TD50/ED50 Therapeutic index: measure of the relative safety of drug PRINCIPLES OF PHARMACOKINETICS Pharmacokinetics – What the body does to the drug study of the different process a drug undergoes as it reaches Differentiate Competitive from Non-competitive antagonist and leaves the biologic state A. PROCESSES Transport processes Liberation Absorption Distribution Competitive antagonism: Shift of the graph to right Metabolism Elimination Excretion Module 4 – Biopharmaceutics Page 5 of 8 RJAV 2022  1. TRANSPORT PROCESSES ii. Facilitated diffusion ATP – independent Mechanism of drug movement across the cell membrane Movement along concentration gradient Passive Transport c. Convective Transport Carrier-mediated Transport Key Properties: Pore size: 7-10 Angstroms, allow passage of drugs with MW < 400-600 Convective Transport Allows passage of ions with charge opposite of pore lining Movement along electrochemical gradient Ion Pair Transport d. Pinocytosis Pinocytosis Key Properties ATP-driven Transport of large lipids in micelle form a. Passive Transport involves movement across a bilipid barrier 2. LIBERATION Dominant No need for ATP Release of drug from the drug product Movement along concentration gradient Drug must be in aqueous solution – required for most Slow transport processes (except pinocytosis) Solid dosage forms → Disintegration → Dissolution Fick’s Law of Diffusion Liquid non-solutions → Dissolution 𝑑𝑄 𝐷. 𝐴. (𝐶1 − 𝐶2) (𝑟𝑎𝑡𝑒 𝑜𝑓 𝑡𝑟𝑎𝑛𝑠𝑝𝑜𝑟𝑡) = 𝑑𝑡 ℎ Noyes-Whitney: Where: D = Diffusion Coefficient 𝑑𝑀 𝐷𝐴(𝐶𝑠 − 𝐶𝑏) A = Surface Area of Membrane = h = Thickness 𝑑𝑡 ℎ (C1 – C2) = Concentration gradient Where: dM/dt = rate of dissolution D = diffusion coefficient Diffusion Coefficient – property of drug dependent on particle size A = surface area of the particle and lipophilicity C = concentration in the stagnant layer Cb = concentration in the bulk layer Surface Area of Membrane – the greater the surface area the h = thickness of the stagnant layer faster the rate (Ling > Small Intestine > Stomach) Thickness – inversely related Intermediate vs Modified-Release Dosage Forms Concentration gradient – concentration from where the drug is coming from and the concentration where the drug is going to Increased Diffusion Coefficient: Smaller particle size Increases surface area contact with cell membrane Application: micronization to improve bioavailability of Rifampicin Greater lipophilicity Less degree of ionization or dissociation into charged molecules/ions 3. ABSORPTION Weakly acidic drug in an acidic environment (lower pH) Weakly basic drug in a less acidic (basic or higher pH) Pharmacokinetic: rate and extent of a drug entry into the environment systemic circulation High lipid-water partition coefficient Physiologic: rate and extent of disappearance of the drug Experimental procedure: solubility in an octanol-water from the site of administration or absorption system Lipid-water partition coefficient: ratio of solubility in lipid Factors affecting absorption: (octanol) to solubility in water a. Dose size b. Carrier-mediated Transports ↑ Dose = ↑ Rate and Extent b. pH of the absorbing environment Common Properties of Carriers: Acidic environment for weak acids, basic environment for weak bases = ↑ Rate and Extent 1. Specificity/ Selectivity: carrier recognizes only certain molecular c. Degree of perfusion of the absorbing environment = blood configuration/ conformation supply L-DOPA vs Dopamine ↑ Blood supply = ↑ Rate and Extent d. Surface area of the absorbing organ 2. Subject to competition/ inhibition/ antagonism: molecules with ↑ Surface Area = ↑ Rate and Extent similar configuration/ confirmation will compete for the same carrier e. Gastric emptying time L-DOPA vs 3-O-methyl-DOPA ↑ GET = ↓ Rate 3. Saturability: limited number of carriers Gastric Emptying Time i. Active transport GET = 1/GER (reciprocal relationship of Time with rate) ATP – dependent Increase GET = Decrease Rate of Absorption Movement against concentration gradient (at least one) Stress, Vigorous exercise, Gastric ulcer, Lying on the Fast left side, anti-motility drugs (anticholinergics, opioids) Module 4 – Biopharmaceutics Page 6 of 8 RJAV 2022  Decrease GET = Increase Rate of Absorption How it is done Mild exercise, Extremes of food temperature, 90% Confidence Interval Gastrectomy, Duodenal ulcer, Lying on the right side, AUC = 80 – 125% DM, promotility drugs (D2-antagonists) Cmax = 30 – 125% Tmax = 80 – 125% Measuring Absorption Bioavailability: measure of rate and extent of drug entry into the systemic circulation Blood measurement Urine measurement Measurement of Blood Levels of Drugs at Timed Intervals 4. DISTRIBUTION Time Plasma Concentration 0 hr 0.0 mg/L Process of drug movement from the systemic circulation to 0.5 hr 0.8 mg/L the different body compartments (organs/ tissues) 1.0 hr 1.2 mg/L Objective: 2.0 hr 2.5 mg/L Most biological sites of action are outside the systemic circulation Distribution allows drug to reach the biological site of Measurement of Cumulative Amount of Drugs or Metabolites action Excreted at Timed Intervals Two Distribution Parameters Time Cumulative Amount 0 hr 0.0 mg a. Protein Binding 0.5 hr 18 mg Free Drug ↔ Bound Drug 1.0 hr 40 mg Blood proteins: 2.0 hr 80 mg Albumin: for weak acids α1 acid glycoprotein: for weak bases Globulin: for hormones Amount time = Urine Concentration x Volume Highly protein drugs: Diazepam, Digitoxin, Indomethacin, Cumulative Amount time = Amount time + Amount previous times Tolbutamide, Warfarin, Midazolam Relevance Bioavailability – blood measurement Limit access to compartments Longer duration tmax Drug Displacement (?) b. Volume of Distribution Log Plasma Drug Conc Log Cmax Hypothetical volume of body fluid necessary to dissolve a given dose or amount of drug to a concentration equal to that of the plasma Vd = D / CO (D = dose size, CO = concentration at time 0) Vd = A / CP (A = amount of drug, CP = drug plasma conc) Relevance AUC Estimating loading doses Loading Dose (DL) = Vd x C desired Predicting fluid compartment of distribution time Fluid Compartment % Body Weight Volume in a 70kg patient Parameters: Total Body Water 60% 42 liters a. Intracellular Water 40% 28 liters Cmax – rate and extent b. Extracellular Water 20% 14 liters Tmax – rate i. Interstitial Water 15% 10-11 liters AUC – extent ii. Intravascular Water 5% 3-4 liters Absolute Bioavailability (Fabs) Drug A: Vd (70kg patient) = 5,000 liters Total body water Drug B: Vd (70kg patient) = 40 liters Total body water High Vd 𝐴𝑈𝐶(𝑡𝑒𝑠𝑡 𝑑𝑟𝑢𝑔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡) 𝐹𝑎𝑏𝑠 = Drug C: Vd (70kg patient) = 30 liters Intracellular 𝐴𝑈𝐶(𝑠𝑎𝑚𝑒 𝑑𝑜𝑠𝑒 𝑜𝑓 𝑑𝑟𝑢𝑔 𝑔𝑖𝑣𝑒𝑛 𝐼𝑉) Drug D: Vd (70kg patient) = 2 liters Intravascular Low Vd Relative Bioavailability (Frel) Drugs with high Vd Drugs with low Vd Atropine Chlorpramide 𝐴𝑈𝐶(𝑡𝑒𝑠𝑡 𝑑𝑟𝑢𝑔 𝑝𝑟𝑜𝑑𝑢𝑐𝑡) Chloroquine Furosemide 𝐹𝑟𝑒𝑙 = Digoxin Tolbutamide 𝐴𝑈𝐶(𝑠𝑎𝑚𝑒 𝑑𝑜𝑠𝑒 𝑜𝑓 𝑛𝑜𝑛−𝐼𝑉 𝑐𝑜𝑚𝑝𝑎𝑟𝑎𝑡𝑜𝑟 𝑜𝑟 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑑𝑟𝑢𝑔) Fluoxetine Valproic acid Imipramine Warfarin Bioequivalence TCAs Measure of similarity in bioavailability of generic drug product BBs to that of the innovator or reference drug product Measures: 90% confidence interval about the ratios of AUC, 5. METABOLISM Cmax and Tmax: AUC ratio = AUC generic / AUC innovator Biotransformation: chemical change Cmax ratio = Cmax generic / Cmax innovator Tmax ration = Tmax generic / Tmax innovator First Pass Effect/ First Pass Metabolism (FPE/FPM) Acceptable 90% confidence interval: 80 – 125% (extended to Initial metabolism a drug undergoes before reaching the 75 – 133% for Cmax) systemic circulation Minimum Number: 12 (immediate release), 20 (controlled Outcomes: release) Goals: metabolites that are Less active/ inactive Less toxic/ Polar and easily excreted Module 4 – Biopharmaceutics Page 7 of 8 RJAV 2022  Exceptions CYP3A4: indinavir, nelfinavir, ritonavir, saquinavir, Prodrug → Active telithromycin, aprepitant, erythromycin, fluconazole, Active → Active grapefruit juice, verapamil Non-toxic → Toxic Genetic Polymorphism: Genetic differences in the expression of Phase of Drug Metabolism enzymes Phase I: Functionalization Phase Categories based on enzyme expression: Addition or unmasking of a functional group a. EM (extensive metabolizers) Reactions: Oxidation, Reduction, Hydrolysis produce normal/ adequate amount of enzymes Phase II: Conjugation or Synthetic Phase b. UM (ultra-rapid metabolizers) Addition of a polar conjugate produce more than the normal amount of enzymes Glucuronidation, Acetylation. Glycine conjugation, etc. c. PM (poor metabolizers) Phase I → Phase II or Phase II → Phase I produce less than the normal amount of enzymes Phase I: a. Oxidation (CYP-mediated) Common enzyme system subject to polymorphism CYP Substrate CYP2D6 1A2 Theophylline, Caffeine, Duloxetine, Melatonin, Clozapine, PM: increase risk of cardiotoxicity with thioridazine and anti- Ramosetron depressants (poor Debrisoquin metabolism) 2B6 Cyclophosphamide, Ifosfamide, Bupropion, Efavirenz NAT2 (N-acetyltransferase-2) 2C8 Repaglinide, Montelukast, Pioglitazone PM: slow acetylators, have higher risk of side effects with 2C9 Celecoxib, Phenytoin, 2nd Gen Sulfonylureas, Tolbutamide, S- substrates of acetylation (procainamide, hydralazine, Warfarin Isoniazid) 2C19 Omeprazole, Lansoprazole, Rabeprazole, Diazepam, EM: rapid acetylators Voriconazole, S-Mephenytoin 2D6 Desipramine, Dextromethorphan, Eliglustat, Nebivolol, Nortriptyline, Perphenazine, Tolterodine, Venlafaxine, 6. EXCRETION Amitriptyline, Encainide, Imipramine, Metoprolol, Propafenone, Propranolol, Tramadol, Trimipramine Elimination 3A4 Macrolides, Amiodarone, Cortisol, Diazepam, Grapefruit juice Metabolism and Excretion Excretion: loss of the drug from the body b. Reduction Site: Kidneys (major), Biliary, Lungs, Nitro-reduction: Chloramphenicol Sweat/Secretions, Mammary Carbonyl reduction: Naloxone, Methadone Prerequisite: Drugs must be polar or water soluble Azo reduction: Prontosil PK Parameters c. Hydrolysis Esters: Procaine, Aspirin, Enalapril (prodrug), Cocaine Biological half-life (metab = benzoic acid) t ½ = 0.693/k Amides: Lidocaine, Indomethacin, Procainamide Time it takes for the amount of drug in the body to be reduced to half its current amount Phase II: a. Glucuronidation No. of t ½ elapsed % Remaining in the body Acetaminophen, Diazepam, Chloramphenicol, Digoxin, 0 100 Morphine 1xt½ 50 Enzyme: UDP-Glucuronosyl Transferase 2xt½ 25 3xt½ 12.5 b. Acetylation 4xt½ 6.25 Isoniazid, Hydralazine, Procainamide 5xt½ 3.125 Enzyme: NAT1 and NAT2 Predicts when a steady state level is achieved when drug c. Glycine conjugation doses are given at regular intervals Nicotinic acid No. of t ½ elapsed % to reach steady state level d. Glutathione conjugation 0 0 Ethacrynic acid 1xt½ 50 2xt½ 75 3xt½ 87.5 e. Methylation 4xt½ 93.75 Dopamine 5xt½ 96.875 Enzyme inhibition-induction Clearance (CL) Enzyme inducers: Benzo[a]pyrene, Phenobarbital, Phenytoin, Volume of blood that is cleared of the drug per given time Rifampicin CL = k*Vd k = elimination rate constant CYP1A2: broccoli, brussel sprouts, char-grilled meat CL = (0.693/t ½) * Vd (benzo[a]pyrene), omeprazole, tobacco CYP2C9: rifampin Total Clearance (CLtotal) = CLrenal + CLliver + CLother sites CYP2C19: rifampin CYP2D6: rifampin, dexamethasone CYP3A4: rifampin, Phenobarbital, St. John’s wort, Carbamazepine, glucocorticoids Enzyme inhibitors: CYP1A2: fluvoxamine, ciprofloxacin CYP2C9: fluconazole, amiodarone CYP2C19: PPI except pantoprazole (for Clopidogrel activation) CYP2D6: fluoxetine, paroxetine, quinidine, duloxetine, terbinafine Module 4 – Biopharmaceutics Page 8 of 8 RJAV 2022