Lecture 3 Distribution Protein Binding Protein Binding Biotransformation Biotransformation

Metabolic Comparison IV vs Oral Drugs given IV reach the systemic circulation immediately and can pass to most target sites for action. They are metabolized during this passage in various locations and reach their excretory sites in either a metabolized degraded less or inactive form. Orally given drugs after ingestion reach the stomach where some amount is absorbed. The major part goes to the liver, through the hepatic circulation where it is metabolized (First Pass Effect) and sent for excretion.

Distribution, Protein Binding & Biotransformation Objectives – Objectives – To explain the distribution of drugs To explain the distribution of drugs To explain the phenomenon of binding of drugs to proteins in plasma To explain the phenomenon of binding of drugs to proteins in plasma To discuss the process of biotransformation of drugs To discuss the process of biotransformation of drugs.

Distribution of a drug 1. Blood and plasma 2. Body water ( ICF & ECF ) 3. Skeletal muscles and bones 4. Organs, tissues (incl fat), cells 5. Secretions 6. Cavities and sinuses 7. Urine and GIT contents 8. Abnormal fluids e.g. oedema, ascitis, pleural effusion

Biotransformation & Excretion Biotransformation (Metabolism) Liver is the major site of biotransformation Liver is the major site of biotransformation Usually leads to formation of inactive metabolites. Usually leads to formation of inactive metabolites. Sometimes a drug is metabolized to active or toxic metabolites. Sometimes a drug is metabolized to active or toxic metabolites. Excretion – Either as unchanged drug or as metabolites Either as unchanged drug or as metabolites Kidney is the major organ of excretion Kidney is the major organ of excretion Other routes: lungs, saliva, feces, milk etc. Other routes: lungs, saliva, feces, milk etc.

Protein binding & Distribution of drugs Drugs exist in plasma as free fraction & protein bound fraction. Drugs exist in plasma as free fraction & protein bound fraction. Protein bound fraction of a drug remains in blood as it does not cross cell membranes while free fraction enters tissues and produces action. Protein bound fraction of a drug remains in blood as it does not cross cell membranes while free fraction enters tissues and produces action. Drugs which cross placenta can affect the fetus. Drugs which cross placenta can affect the fetus.

Biotransformation Sites & Reasons Biotransformation Sites & Reasons Sites Tissue, LIVER, GIT, Lungs, skin, Kidney Reasons 1. Renal excretion play a pivotal role in termination of biological activity of some drugs, (small molecular volumes or polar and fully ionized types) 2. Many drugs are not as above and are lipophilic and partly or totally un-ionized. Strongly bound to plasma proteins so not excretable. Strongly bound to plasma proteins so not excretable. In these states the kidney does not excrete – the drug will remain in the body – have prolonged unnecessary biological effects. In these states the kidney does not excrete – the drug will remain in the body – have prolonged unnecessary biological effects. 3. Metabolism (Biotransformation – often a protective mechanism) comes into play to make the drug into an excretable product.

Acids and Enzymes Acids and Enzymes GIT Degradation by gastric acid – Penicillin Degradation by digestive enzymes – Insulin Degradation by enzymes in the wall of the intestine – Catecholamines Sub cellular locations of enzymes (involved in digestion of drugs) a) Endoplasmic reticulum (b) Mitochondria c) Cytosol (d) Lysosomes e) Nuclear envelope (f) Plasma membrane

Metabolism - Reactions Reactions are divided into Type 1 & 2. Reactions are divided into Type 1 & 2. Type 1 are :OXIDATIONS:- Type 1 are :OXIDATIONS:- Cytochrome P450 dependent oxidations Cytochrome P450 dependent oxidations a) Aromatic hydroxylations e.g. Acetanilide, Warfarin a) Aromatic hydroxylations e.g. Acetanilide, Warfarin Phenobarbitone, Phenylbutazone Phenobarbitone, Phenylbutazone b) Aliphatic hydoxylation e.g. Amobarbitone, Secobarbitone, Glutethimide, Digitoxin b) Aliphatic hydoxylation e.g. Amobarbitone, Secobarbitone, Glutethimide, Digitoxin c) Epoxidation e.g. Aldrin c) Epoxidation e.g. Aldrin Oxidative dealkylation Oxidative dealkylation a) N-dealkylation e.g. Morphine, benzamphetamine, caffeine, theabain a) N-dealkylation e.g. Morphine, benzamphetamine, caffeine, theabain b) O-dealkylation e.g. Codeine b) O-dealkylation e.g. Codeine c) S-dealkylation e.g. 6 Methylthiamine c) S-dealkylation e.g. 6 Methylthiamine N-Oxidation N-Oxidation a) Primary amines e.g. Aniline a) Primary amines e.g. Aniline b) Secondary amines e.g. Acetaminophen b) Secondary amines e.g. Acetaminophen c) Tertiary amines: e.g. Nicotine c) Tertiary amines: e.g. Nicotine S-Oxidation e.g. Thioridazine, Chlorpromazine S-Oxidation e.g. Thioridazine, Chlorpromazine Deamination e.g. Amphetamine Deamination e.g. Amphetamine Desulfuration e.g. Thiopental Desulfuration e.g. Thiopental

Reactions - Type 2 Types Types of of Conjugation Conjugation Endogenous Endogenous Reactant Reactant Transferase Transferase & Location Location Types Types of of Substrates Substrates Examples Examples Glucorinidation Glucorinidation UDP glucuronic acid acid UDP glucoronosyl- transferase (microsomes) Phenols, alcohols, carbolic acids, hydroxylamines, sulfonamidesNitrophenol, Morphine, acetoaminophen diazepam, N- hydroxydapsone, sulphathiazole,meprobamate, digitoxin, digoxin Acetylation Acetylation Acetyl-CoA Acetyl-CoAN-Acetyltransferase (Cytosol) (Cytosol) Amines Amines Sulfonamides, INH, dapsone, Clonazepam,mescaline Glutathione Glutathione conjugation conjugation Glutathione GlutathioneGSH-S-transferase (Cytosol, microsomes) Epoxides, areneoxides, Nitrogroups,hydroxylamines Ethacrynic acid bromobenzene Glycine conjugation Glycine conjugation Glycine GlycineAcyl-CoAGlycine-transferase (mitochondria) (mitochondria) Acyl-CoA derivatives of Carbolic acid Salicylic acid Benzoic acid, Nicotinic acid, Cholic acid Deoxycholic acid Cinnamic acid

Reaction 2 (continued) Type Type Endogenous Endogenous Reactant ReactantTransferase(Location) Types of substrateExamples Sulphate Sulphate conjugation conjugationPhosphoadenosylphosphosulphateSulphotransferase (Cytosol) (Cytosol) Phenols, alcohols, Aromatic amines Esterone, aniline Phenol, 3- hydroxy-coumarin Acetaminophenmethyldopa Methylation Methylation S-adenosyl- S-adenosyl- methionine methionineTransmethylases (Cytosol) (Cytosol)Cathecholamines Amines, phenols Dopamine,EpinephrinePyridineHistaminethiouracil Water Water conjugation conjugation Water Water Epoxide Epoxide hydroxylase hydroxylase (microsomes) (microsomes) (cytosol) (cytosol) Arene oxides, oxiranes Alkene oxides Fatty acid epoxides BenzopyrineCarbamazepineEpoxide Leukotriene A 4

Factors modifying drug distribution & Rates of metabolism & elimination Age Age Sex Sex Liver size & function Liver size & function Circadian rhythm Circadian rhythm Body temperature Body temperature Nutritional & environmental factors Nutritional & environmental factors Concomitant use of inducers or inhibitors Concomitant use of inducers or inhibitors Genetic factors Genetic factors

Clinical Implications of Genetic Polymorphisms in drug metabolism Defect Defect Drug Drug ( Use ) ( Use ) Clinical Clinicalconsequences Oxidation Oxidation Bufuralol Bufuralol (ß adrenoreceptor blocker ) (ß adrenoreceptor blocker ) Exacerbation of blockade Nausea Oxidation Oxidation Codeine Codeine (analgesic) (analgesic) Reduced analgesia Oxidation Oxidation Debrisoquin Debrisoquin (antihypertensive) (antihypertensive) Orthostatic hypotension N-Demethylation N-Demethylation Ethanol Ethanol Facial flushing CVS symptoms Oxidation Oxidation Ethanol Ethanol Facial flushing CVS symptoms N-Acetylation N-Acetylation Hydralazine Hydralazine (antihypertensive) (antihypertensive) Lupus Erythematosus – like Syndrome N-Acetylation N-Acetylation INH INH (antitubercular) (antitubercular) Peripheral neuropathy

Pharmacogenetics & Clinical Implications 2 Defect Defect Drug Drug (Therapeutic Use) (Therapeutic Use) Clinical Clinical Consequences Consequences Thiopurine Thiopurine methyltransferase methyltransferase Mercaptopurines Mercaptopurines (antileukaemic) (antileukaemic)Myelotoxicity Oxidation Oxidation Nicotine Nicotine (stimulant) (stimulant) Lesser addiction Oxidation Oxidation Nortryptaline Nortryptaline (antidepressant) (antidepressant) Toxicity O-Demethylation O-Demethylation Omeprazole Omeprazole (antiulcer) (antiulcer) Increased therapeutic efficacy Oxidation Oxidation Sparteine Sparteine Oxytocic symptoms Ester hydrolysis Ester hydrolysis Succinylcholine Succinylcholine (neuromuscular blocker) (neuromuscular blocker) Prolonged apnea Oxidation Oxidation S-warfarin S-warfarin (anticoagulant) (anticoagulant)Bleeding Oxidation Oxidation Tolbutamide Tolbutamide (hypoglycemic) (hypoglycemic)Cardiotoxicity Oxidation Oxidation Mephenytoin (anti epileptic) Overdose toxicity

Metabolism Enhancers a partial list Inducer Inducer Drugs whose metabolism is enhanced Drugs whose metabolism is enhanced Benzo(a)pyreneTheophylline Chlorcyclizine Steroid hormones EthchlorvynolWarfarin Glutethimide Antipyrene, glutethimide, warfarin GriseofulvinWarfarin Phenobarbital & other Barbiturates Barbiturates, chloramphenicol, chlorpromazine, cortisol, coumarin, Anticoagulants, desmethylimipramine, digitoxin, doxorubicin, estradiol, Phenylbutazone, phenytoin, quinine, testosterone Phenylbutazone Aminopyrine, cortisol, digitoxin Phenytoin Cortisol, dexamethasone, digitoxin, theophylline Rifampin Coumarins, digitoxin, gluco corticoids, methadone, metoprolol, OCPs, Prednisone, propanolol, quinidine

Metabolism Inhibitors a partial list Allopurinol, INH Chloramphenicol Antipyrene, dicoumarol, probenecid, tolbutamide Cimetidine Chlordiazepoxide, diazepam, warfarin and others DicoumarolPhenytoin Disulfiram Antipyrine, ethanol, phenytoin, warfarin Ethanol Chlordiazepoxide? Diazepam ? Methanol Grape fruit juice Alprazolam, atorvastatin, cisapride, cyclosporine, midazolam, triazolam Ketoconazole Cyclosporine, astemizole, terfenadine NortryptalineAntipyrine OCPsAntipyrine Phenylbutazone Phenytoin, Tolbutamide Troleandomycin Theophylline, methylprednisolone

Learning outcomes The learner should be able to The learner should be able to State the various sites of drug distribution in the body with significance of importance of such distribution giving examples. State the various sites of drug distribution in the body with significance of importance of such distribution giving examples. List Plasma proteins to which drugs are bound and the explain the significance of plasma protein binding in therapeutics. List Plasma proteins to which drugs are bound and the explain the significance of plasma protein binding in therapeutics. To explain the process of biotransformation of drugs with its clinical relevance citing examples To explain the process of biotransformation of drugs with its clinical relevance citing examples