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DRUG EXCRETION

DRUG EXCRETION. DRUG EXCRETION. The process by which drugs or metabolites are irreversibly transferred from internal to external environment through renal or non renal route. Most drugs are excreted in urine either as unchanged drugs or drug metabolites. TYPES OF EXCRETION. RENAL EXCRETION

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DRUG EXCRETION

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  1. DRUG EXCRETION

  2. DRUG EXCRETION • The process by which drugs or metabolites are irreversibly transferred from internal to external environment through renal or non renal route. • Most drugs are excreted in urine either as unchanged drugs or drug metabolites.

  3. TYPES OF EXCRETION • RENAL EXCRETION • NON RENAL EXCRETION • Biliary excretion. • Pulmonary excretion. • Salivary excretion. • Mammary excretion. • Skin / Dermal excretion. • Gastrointestinal excretion. • Genital excretion.

  4. RENAL EXCRETION

  5. ANATOMY OF NEPHRON

  6. Glomerular filtration Tubular secretion Tubular re-absorption Major Excretory Processes in the Nephron

  7. GLOMERULAR FILTRATION It Is non selective , unidirectional process Ionized or unionized drugs are filtered, except those that are bound to plasma proteins.

  8. ACTIVE TUBULAR SECRETION This mainly occurs in proximal tubule. Active secretion is Unaffected by change in pH and protein binding.

  9. PASSIVE TUBULAR REABSORPTION most substances are reabsorbed across renal tubular cells if unionized and lipid soluble It occurs after the glomerular filtration of drugs. It takes place all along the renal tubules. Reabsorption results in increase in the half life of the drug.

  10. pH OF THE URINE • It varies between 4.5 to 7.5 • It depends upon diet, drug intake and pathophysiology .

  11. Acidic drugs usually contain weakly acidic functionalities, such as COOH. Basic drugs usually contain weakly basic functionalities, such as amines. Drugs which are acidic are ionized in basic media (pH > 7). Drugs which are basic are ionized in acidic media (pH < 7) The ionized form of the drug provides it with improved water solubility But the unionized form generally passes nonpolar membranes more readily. Acidification of urine increases reabsorption and decreases excretion of weak acids and decreases reabsorption of weak bases. Alkalinization of urine has the opposite effect. In some cases of overdose, these principles are used to enhance the excretion of weak bases or acids. e.g. salicylate (Aspirin ) (a weak acid) overdose may be treated by making the urine more alkaline with sodium bicarbonate injection.

  12. Effect of lipid solubility and pH ionised drug is less lipid soluble Glomerular blood flow; filtrate 99% of GF is re-absorbed; concentration of drug rises in tubule If lipid soluble drug moves down concentration gradient back into blood Re-absorption

  13. FACTORS AFFECTING RENAL EXCRETION Physicochemical properties of drug Molecular size: Drugs with Mol.wt <300, water soluble are excreted in kidney. Mol.wt 300 to 500 Dalton are excreted both through urine and bile. Binding characteristics of the drug: Drugs that are bound to plasma proteins behave as macromolecules and cannot be filtered through glomerulus. Only unbound or free drug appear in glomerular filtrate. Protein bound drug has long half lives. Biological factor:Age, sex 3. Drug interaction: increase or decrease 4. Disease state Urine pH: RF 5. Blood flow to the kidney

  14. NON-RENAL ROUTE OF DRUG EXCRETION Various routes are Biliary Excretion Pulmonary Excretion Salivary Excretion Mammary Excretion Skin/dermal Excretion Gastrointestinal Excretion Genital Excretion

  15. PULMONARY EXCRETION Gaseous and volatile substances such as general anesthetics (Halothane) are absorbed through lungs by simple diffusion. Pulmonary blood flow, rate of respiration and solubility of substance effect PE. Intact gaseous drugs are excreted but not metabolites. Alcohol which has high solubility in blood and tissues are excreted slowly by lungs.

  16. SALIVARY EXCRETION The pH of saliva varies from 5.8 to 8.4. Unionized lipid soluble drugs are excreted passively. The bitter after 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.

  17. MAMMARY EXCRETION 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..

  18. SKIN EXCRETION Drugs excreted through skin via sweat 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.

  19. GASTROINTESTINAL EXCRETION Excretion of drugs through GIT usually occurs after parenteral administration. Water soluble and ionized from of weakly acidic and basic drugs are excreted in GIT. Example are nicotine and quinine are excreted in stomach. Drugs excreted in GIT are reabsorbed into systemic circulation & undergo recycling.

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