General principles of drug action


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General principles of drug action

  1. 1. Chapter 2 General Principles of Drug Action
  2. 2. General Factors that Characterize the action of all Drugs and that Determine the effective level of any Therapeutic agent at its site of action <ul><li>Route of administration </li></ul><ul><li>Passage across body membrane </li></ul><ul><li>Absorption </li></ul><ul><li>Transport and distribution </li></ul><ul><li>Molecular mechanism of drug action </li></ul><ul><li>Drug metabolism </li></ul><ul><li>excretion </li></ul>
  3. 3. A. Route of administration <ul><li>General Routes of Drug Administration </li></ul><ul><li>I. Enteral- (Oral and Rectal) </li></ul><ul><li>Oral </li></ul><ul><li>Dosage forms: tablet, capsule, suspension, </li></ul><ul><li>solution, pills etc. </li></ul><ul><li>Area of Absorption: gastric and intestinal mucosa </li></ul>
  4. 4. oral <ul><li>Advantages </li></ul><ul><li>- Safest </li></ul><ul><li>- Most convenient </li></ul><ul><li>- Cheapest </li></ul><ul><li>Disadvantages </li></ul><ul><li>Irritation of the gastric mucosa </li></ul><ul><li>Destruction of some drugs by the gastric acid </li></ul><ul><li>Variable rate of absorption </li></ul><ul><li>Slow rate of absorption </li></ul>
  5. 5. II. Parenteral ( IV, IM, SC ID)
  6. 6. Intravenous <ul><li>Advantages </li></ul><ul><li>Most rapid and uniform response </li></ul><ul><li>More predictable response </li></ul><ul><li>Useful for administering drugs that poorly absorbed by other routes </li></ul><ul><li>Disadvantages </li></ul><ul><li>Produces more side effects </li></ul><ul><li>Drugs can not be withdrawn once injected </li></ul>
  7. 7. Sublingual routes <ul><li>Area of absorption : oral mucous membrane </li></ul><ul><li>Drug is placed under the tongue </li></ul><ul><li>By- Passed effect </li></ul><ul><li>Example of drug: Nitroglycerine </li></ul>
  8. 8. B. Passage Across Body Membrane <ul><li>Types of Body Membrane </li></ul><ul><ul><li>Cell membrane </li></ul></ul><ul><ul><li>Intracellular membrane </li></ul></ul><ul><ul><li>Blood capillaries </li></ul></ul>
  9. 9. <ul><li>Composition </li></ul><ul><ul><ul><li>Phospholipid (40%) </li></ul></ul></ul><ul><ul><ul><li>Protein (50-60% </li></ul></ul></ul>
  10. 10. <ul><li>Physiochemical properties </li></ul><ul><ul><ul><li>Lipid solubility </li></ul></ul></ul><ul><ul><ul><li>Molecular size and shape </li></ul></ul></ul><ul><ul><ul><li>Degree of ionization </li></ul></ul></ul><ul><ul><ul><ul><li>pH </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Pka </li></ul></ul></ul></ul>
  11. 11. Types of Passage ( Transport) <ul><li>I. Passive transport </li></ul><ul><ul><ul><li>Simple diffusion </li></ul></ul></ul><ul><ul><ul><li>filtration </li></ul></ul></ul><ul><li>II Specialized transport </li></ul><ul><ul><ul><li>Active transport </li></ul></ul></ul><ul><ul><ul><li>Facilitated diffusion </li></ul></ul></ul><ul><ul><ul><li>Pinocytocis </li></ul></ul></ul>
  12. 12. C. Absorption <ul><li>movement of molecules from the site of administration to the blood stream </li></ul>
  13. 13. Factors Affecting Absorption <ul><li>Physiochemical factors that affect passage </li></ul><ul><li>Dosage form (bioavailability) </li></ul><ul><li>Drug solubility </li></ul><ul><li>Area of absorbing surface </li></ul><ul><li>Drug concentration </li></ul><ul><li>Blood flow </li></ul>
  14. 14. D. Distribution <ul><li>Movement of molecules from the blood stream to the different tissues of the body </li></ul>
  15. 15. Factors Contributing to the unequal rate of Distribution <ul><li>Plasma protein binding </li></ul><ul><li>Cellular binding </li></ul><ul><li>Storage in body fats </li></ul><ul><li>Blood-Brain Barrier </li></ul>
  16. 16. E. Molecular Mechanism of Drug action <ul><li>Receptors </li></ul><ul><li>Affinity </li></ul><ul><li>Agonist </li></ul><ul><li>Antagonist </li></ul>
  17. 17. Factors affecting Drug activity <ul><li>Antagonism </li></ul><ul><li>a. pharmacologic </li></ul><ul><li>e.g. histamine + antihistamine </li></ul><ul><li>b. physiologic </li></ul><ul><li>e.g. diuretics + sympathomimetic amide </li></ul><ul><li>c. chemical </li></ul><ul><li>e.g. heparin + protamine </li></ul><ul><li>2. Additve effect </li></ul><ul><li>3. Potentiation </li></ul><ul><li>4. Cummulation </li></ul><ul><li>5. Tolerance /tachyphylaxis </li></ul><ul><li>6. Variation in drug response </li></ul>
  18. 18. Drug Termination <ul><li>Redistribution </li></ul><ul><li>Excretion (kidney) </li></ul><ul><li>Amount of drug excreted by the kidney depends on the following process </li></ul><ul><li> 1. passive tubular diffusion ( reabsorption) </li></ul><ul><li>2. active tubular secretion </li></ul><ul><li> 3. filtration </li></ul><ul><li>* Metabolism </li></ul>
  19. 19. Chapter 3 Adverse Drug Reactions
  20. 20. <ul><li>Classification </li></ul><ul><li>1. Toxic </li></ul><ul><li>a. exaggerated effect on target organ </li></ul><ul><li>b. effects on non target organ (side effect) </li></ul><ul><li>c. effects on fetal development ( terratogenic) </li></ul><ul><li>d. local reaction </li></ul><ul><li>e. drug interactions </li></ul><ul><li>2. Allergic reactions </li></ul><ul><li>3. Idiosyncrasy </li></ul><ul><li>4. Interference in natural defense mechanism </li></ul>
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