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1 lab physico-chemical_properties_of_drugs[1]


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1 lab physico-chemical_properties_of_drugs[1]

  2. 2. PHYSICO-CHEMICAL PROPERTIES OF DRUGS Physical Chemical Solubility and Permeability Partition Coefficient Physical State Isomerism Polarity Intermolecular Forces Particle Size Ionization Melting Point pH Functional Group
  3. 3. PHYSICAL PROPERTIES  Solubility  first requirement for drug absorption • less or no solubility yields minimal or no response/effect from the drug  Permeability  way how substances “travel through” cellular membranes • poor permeability can lead to poor absorption across the GI mucosa or poor distribution throughout the body
  4. 4. PHYSICAL PROPERTIES Solid Dosage Form Solid Drug Particles Drug in solution at absorption site Drug in the body disintegration dissolution permeation
  5. 5. PHYSICAL PROPERTIES Drug Classification according to Solubilty/Permeability Class Solubility Permeability Absorption Pattern Rate Limiting Step Example I High High Well absorbed Gastric Emptying Diltiazem II Low High Variable Dissolution Nifedipine III High Low Variable Permeation Insulin IV Low Low Poorly absorbed Case by case Taxol
  6. 6. PHYSICAL PROPERTIES  Physical State  solid drugs needs to dissociate to exert its effect, thus it will take time to elicit a response compared to a drug in liquid form.
  7. 7. PHYSICAL PROPERTIES  Physical State Order of Absorption Modified Release Tablets Enteric Tablets Coated Tablets Compressed Tablets Capsules Suspensions Emulsions Solutions
  8. 8. PHYSICAL PROPERTIES  Polarity “LIKE DISSOLVES LIKE”  To get across most membranes, the drug must be relatively NON-POLAR (lipophilic)  To be soluble in water, a drug must be POLAR (hydrophilic)
  9. 9. PHYSICAL PROPERTIES  Particle Size smaller particle size higher dissolution rate faster absorption  Melting Point lower melting point faster absorption
  10. 10. CHEMICAL PROPERTIES  Partition Coefficient  for a drug to be orally absorbed, it must pass through lipid bilayers in the intestinal mucosa. low lipid solubility poor absorption
  11. 11. CHEMICAL PROPERTIES  Isomerism  drug molecules must generally interact with biomolecules (enzymes/receptors) in a very SPECIFIC way to elicit a pharmacological response  many drugs are optically active and have different actions in relation to its spatial arrangement
  12. 12. CHEMICAL PROPERTIES Constitutional Isomers  Pentobarbital (short-acting)  Amobarbital (intermediate-acting)
  13. 13. CHEMICAL PROPERTIES Enantiomers (R) Isomers  (R) Naproxen (inactive) (S) Isomers  (S) Naproxen (NSAID)
  14. 14. CHEMICAL PROPERTIES Diastereomers Cis Isomers - Only 7% active Trans Isomers - Estrogenic
  15. 15. CHEMICAL PROPERTIES Geometric Isomers E Isomers Z Isomers Clomiphene - Ovulation Stimulant
  16. 16. CHEMICAL PROPERTIES Diastereomers Dextrorotatory Isomers  Dextrorphan (anti-tussive) Levorotatory Isomers  Levorphanol (analgesic)
  17. 17. CHEMICAL PROPERTIES  Intermolecular Forces ― drugs interact and bind to the binding sites (receptors/proteins/enzymes) through intermolecular forces ― relatively weak forces must be involved in the drug- receptor complex yet be strong enough that other binding sites will not competitively deplete the site of action
  18. 18. CHEMICAL PROPERTIES  Intermolecular Forces  covalent bonds – long lasting or irreversible effects are desired. e.g. antineoplastic agents, antibacterials  ionic bonds  hydrogen bonds  Van der waals forces  dipole-dipole  ion-dipole  hydrophobic bonds Reversible; Desired bonds for most drugs
  19. 19. CHEMICAL PROPERTIES  pH  most drugs are weak acids and weak bases  an acidic drug dissolves in a basic medium  a basic drug dissolves in an acidic medium  pH in different body compartments  Plasma 7.35 – 7.45  Buccal Cavity 6.2 – 7.2  Stomach 1.0 – 3.0  Duodenum 4.8 – 8.2  Jejunum and ileum 7.5 – 8.0  Colon 7.0 – 7.5
  20. 20. CHEMICAL PROPERTIES  Ionization  only the unionized form of a drug can partition through membranes  the ionized form is more water-soluble (required for drug administration and drug distribution in plasma)
  21. 21. CHEMICAL PROPERTIES  Ionization ionized drug high solubility high absorption low lipid solubility unionized drug high permeability low polarity high lipid solubility
  22. 22. CHEMICAL PROPERTIES  Functional Group  Phase I and II reactions  addition of polar functional groups results in more water soluble and readily excretable metabolites
  23. 23. QUESTIONS 1. What are the requirements for a drug to exert its biological effect? The Drug must:  pass through barriers  survive alternate sites of attachment/storage  avoid metabolic destruction before it reaches the site of action  allow favorable binding characteristics  dissociate from receptor and reenter the systemic circulation to be excreted
  24. 24. QUESTIONS 2. What route of administration will give fast drug action? Intravenous (IV) route of administration
  25. 25. QUESTIONS 3. What are the different forces involved in drug- receptor interaction? Explain.  Covalent Bonds – bond formed by sharing electrons between atoms  Ionic Bonds – bond formed by the attraction between atoms of opposite charge  Hydrogen Bonds – bond formed by hydrogen atoms bound to electronegative atoms
  26. 26. QUESTIONS 3. What are the different forces involved in drug- receptor interaction? Explain.  Ion-Dipole – bond formed from the electrostatic attraction between an ion and a neutral molecule that has a dipole.  Dipole-Dipole – bond formed between the positive end of one polar molecule and the negative end of another polar molecule  Van der waals forces – bond formed when any two uncharged atoms approach each other very closely
  27. 27. QUESTIONS 4. What form of drug is well absorbed and excreted in the body? Intravenous (IV) route of administration
  28. 28. QUESTIONS 5. What is the importance of a drug receptor? What is the principle of Drug-Receptor Interaction? DRUG RECEPTOR DRUG-RECEPTOR COMPLEX PHARMACOLOGICAL EFFECT