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Faraza Javed
PhD Pharmacology
Excretion is defined as a process whereby drugs
or metabolites are irreversibly transferred from
internal to external envi...
Principal organs involved:
Kidneys (Renal Excretion)
Bile (Biliary Excretion)
Lungs (Pulmonary Excretion)
Saliva (Sali...
Drugs are eliminated from the body primarily by
the kidneys.
The principal renal mechanisms that are involved in the
excre...
 The ultrastructure of the glomerular capillary wall is
such that it permits a high degree of fluid filtration
while rest...
 Several factors, including molecular size, charge, and
shape, influence the glomerular filtration of large
molecules.
 ...
 All unbound drugs will be filtered as long as their
molecular size, charge, and shape are not excessively
large.
 Compo...
 The tubular secretion which is carried out at the level
of the proximal tubule is an active process.
 It is carrier med...
Organic Anion Transport Organic Cation Transport
Acetazolamide Acetylcholine
Bile salts Atropine
Hydrochlorothiazide Cimet...
 In the distal tubule there is passive excretion and re-
absorption of drugs. Drugs which are present in the
glomerular f...
 Many drugs are either weak bases or acids and
therefore the pH of the filtrate can greatly influence
the extent of tubul...
 In the case of a drug overdose it is possible to
increase the excretion of some drugs by suitable
adjustment of urine pH...
 Transporters are also present in the canalicular
membrane of the hepatocyte, and these actively
secrete drugs and metabo...
A drug excreted in bile may be reabsorbed from the
gastrointestinal tract or a drug conjugate may be
hydrolyzed by gut bac...
 Such enterohepatic recycling, if extensive, may
prolong significantly the presence of a drug (or toxin)
and its effects ...
 Gases and other volatile substances such as general
anesthetics that enter the body primarily through the
respiratory tr...
 The degree of solubility of a gas in blood also will
affect the rate of gas loss.
 Gases such as nitrous oxide, which a...
The pH of saliva varies from 5.8 to 8.4. Unionized
lipid soluble drugs are excreted passively.
 The bitter taste in the ...
Milk consists of lactic secretions which is rich in fats
and proteins.
 Excretion of drug in milk is important as it gain...
Amount of drug excreted in milk is less than 1% and
fraction consumed by infant is too less to produce
toxic effects. Som...
 Drugs excreted through skin via sweat follows pH
partition hypothesis. Excretion of drugs through skin
may lead to urtic...
EXCRETION PATHWAYS, TRANSPORT
MECHANISMS & DRUG EXCRETED.
Excretory
route
Mechanism Drug Excreted
Urine GF, ATS, PTR Free,...
Pharmacokinetics: Excretion of drugs
Pharmacokinetics: Excretion of drugs
Pharmacokinetics: Excretion of drugs
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Pharmacokinetics: Excretion of drugs Slide 1 Pharmacokinetics: Excretion of drugs Slide 2 Pharmacokinetics: Excretion of drugs Slide 3 Pharmacokinetics: Excretion of drugs Slide 4 Pharmacokinetics: Excretion of drugs Slide 5 Pharmacokinetics: Excretion of drugs Slide 6 Pharmacokinetics: Excretion of drugs Slide 7 Pharmacokinetics: Excretion of drugs Slide 8 Pharmacokinetics: Excretion of drugs Slide 9 Pharmacokinetics: Excretion of drugs Slide 10 Pharmacokinetics: Excretion of drugs Slide 11 Pharmacokinetics: Excretion of drugs Slide 12 Pharmacokinetics: Excretion of drugs Slide 13 Pharmacokinetics: Excretion of drugs Slide 14 Pharmacokinetics: Excretion of drugs Slide 15 Pharmacokinetics: Excretion of drugs Slide 16 Pharmacokinetics: Excretion of drugs Slide 17 Pharmacokinetics: Excretion of drugs Slide 18 Pharmacokinetics: Excretion of drugs Slide 19 Pharmacokinetics: Excretion of drugs Slide 20 Pharmacokinetics: Excretion of drugs Slide 21 Pharmacokinetics: Excretion of drugs Slide 22 Pharmacokinetics: Excretion of drugs Slide 23 Pharmacokinetics: Excretion of drugs Slide 24 Pharmacokinetics: Excretion of drugs Slide 25
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Pharmacokinetics: Excretion of drugs

  1. 1. Faraza Javed PhD Pharmacology
  2. 2. Excretion is defined as a process whereby drugs or metabolites are irreversibly transferred from internal to external environment through renal or non renal route. Excretion, along with metabolism and tissue redistribution, is important in determining both the duration of drug action and the rate of drug elimination.
  3. 3. Principal organs involved: Kidneys (Renal Excretion) Bile (Biliary Excretion) Lungs (Pulmonary Excretion) Saliva (Salivary Excretion) Milk (Mammary Excretion) Sweat (Skin Excretion)
  4. 4. Drugs are eliminated from the body primarily by the kidneys. The principal renal mechanisms that are involved in the excretion of drugs are: 1. Glomerular filtration 2. Active tubular secretion 3. Active tubular reabsorption
  5. 5.  The ultrastructure of the glomerular capillary wall is such that it permits a high degree of fluid filtration while restricting the passage of compounds having relatively large molecular weights.  This selective filtration is important in that it prevents the filtration of plasma proteins (e.g., albumin) that are important for maintaining an osmotic gradient in the vasculature and thus plasma volume.
  6. 6.  Several factors, including molecular size, charge, and shape, influence the glomerular filtration of large molecules.  As the ultrafiltrate is formed, any drug that is free in the plasma water, that is, not bound to plasma proteins or the formed elements in the blood (e.g., red blood cells), will be filtered as a result of the driving force provided by cardiac pumping.
  7. 7.  All unbound drugs will be filtered as long as their molecular size, charge, and shape are not excessively large.  Compounds with 20 Å to 42Å may undergo glomerular filtration.
  8. 8.  The tubular secretion which is carried out at the level of the proximal tubule is an active process.  It is carrier mediated process which requires energy for transportation of compounds against conc. gradient Two secretion mechanisms are identified. System for secretion of organic acids/anions e.g. Penicillin, salicylates etc System for organic base / cations e.g. morphine, mecamylamine hexamethonium
  9. 9. Organic Anion Transport Organic Cation Transport Acetazolamide Acetylcholine Bile salts Atropine Hydrochlorothiazide Cimetidine Furosemide Dopamine Indomethacin Epinephrine Penicillin G Morphine Prostaglandins Neostigmine Salicylate Quinine
  10. 10.  In the distal tubule there is passive excretion and re- absorption of drugs. Drugs which are present in the glomerular filtrate can be reabsorbed in the tubules. A reason for this is that much of the water, in the filtrate, has been reabsorbed and therefore the concentration gradient is now in the direction of re- absorption hence drug may be readily reabsorbed.
  11. 11.  Many drugs are either weak bases or acids and therefore the pH of the filtrate can greatly influence the extent of tubular re-absorption for many drugs. When urine is acidic, weak acid drugs tend to be reabsorbed. Alternatively when urine is more alkaline, weak bases are more extensively reabsorbed. Making the urine more acidic can cause less reabsorption of weak bases or enhanced excretion.
  12. 12.  In the case of a drug overdose it is possible to increase the excretion of some drugs by suitable adjustment of urine pH. For example, in the case of pentobarbital (a weak acid) overdose it may be possible to increase drug excretion by making the urine more alkaline with sodium bicarbonate injection.
  13. 13.  Transporters are also present in the canalicular membrane of the hepatocyte, and these actively secrete drugs and metabolites into bile. e.g. the organic anion transporting polypeptides (OATPs), the P-glycoprotein transport system and the multidrug resistance-associated proteins (Mrps). Drug in bile enters the gastrointestinal tract after storage in the gallbladder. It may then be excreted from the body by the stools.
  14. 14. A drug excreted in bile may be reabsorbed from the gastrointestinal tract or a drug conjugate may be hydrolyzed by gut bacteria, liberating original drug which can be returned to the general circulation. Such recycling may continue (enterohepatic cycle or circulation) until the drug either undergoes metabolic changes in the liver, is excreted by the kidneys, or both.
  15. 15.  Such enterohepatic recycling, if extensive, may prolong significantly the presence of a drug (or toxin) and its effects within the body prior to elimination by other pathways.  Orally administered activated charcoal and/or anion exchange resins have been used clinically to interrupt enterohepatic cycling and trap drugs in the gastrointestinal tract.  Cholestatic disease states, in which normal bile flow is reduced, will influence drug elimination by this route resulting in increased risk of drug toxicity.
  16. 16.  Gases and other volatile substances such as general anesthetics that enter the body primarily through the respiratory tract can be expected to be excreted by this route.  No specialized transport systems are involved in the loss of substances in expired air; simple diffusion across cell membranes is predominant.  The rate of loss of gases is not constant; it depends on the rate of respiration and pulmonary blood flow.
  17. 17.  The degree of solubility of a gas in blood also will affect the rate of gas loss.  Gases such as nitrous oxide, which are not very soluble in blood, will be excreted rapidly, that is, almost at the rate at which the blood delivers the drug to the lungs.  Ethanol, which has a relatively high blood gas solubility, is excreted very slowly by the lungs.
  18. 18. The pH of saliva varies from 5.8 to 8.4. Unionized lipid soluble drugs are excreted passively.  The bitter taste in the mouth of a patient is indication of drug excreted. Some basic drugs inhibit saliva secretion and are responsible for mouth dryness. Compounds excreted in saliva are Caffeine, Phenytoin, Theophylline.
  19. 19. Milk consists of lactic secretions which is rich in fats and proteins.  Excretion of drug in milk is important as it gains entry in breast feeding infants.  pH of milk varies from 6.4 to 7.6. Free un-ionized and lipid soluble drugs diffuse passively.  Highly plasma bound drug like Diazepam is less secreted in milk.
  20. 20. Amount of drug excreted in milk is less than 1% and fraction consumed by infant is too less to produce toxic effects. Some potent drugs like barbiturates and morphine may induce toxicity.
  21. 21.  Drugs excreted through skin via sweat follows pH partition hypothesis. Excretion of drugs through skin may lead to urticaria and dermatitis. Compounds like benzoic acid, salicylic acid, alcohol and heavy metals like lead, mercury and arsenic are excreted in sweat.
  22. 22. EXCRETION PATHWAYS, TRANSPORT MECHANISMS & DRUG EXCRETED. Excretory route Mechanism Drug Excreted Urine GF, ATS, PTR Free, hydrophilic, unchanged drugs/ metabolites of MW< 300 Bile Active secretion Hydrophilic, unchanged drugs/ metabolites/ conjugates of MW >500 Lung Passive diffusion Gaseous &volatile, blood & tissue insoluble drugs saliva Passive diffusion Active transport Free, unionized, lipophilic drugs. Some polar drugs Milk Passive diffusion Free, unionized, lipophilic drugs (basic) Sweat Passive diffusion Free, unionized lipophilic drugs
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Hope, it ll help u understand better about the mechanism of excretion of drugs via different routes.

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