biopharmaceutics 3

• What are the two factors influencing bioavailability?

  Dissolution rate and permeation rate
• What dictates permeability in drug absorption?

  Apical membranes composed of lipids and proteins
• What are the types of transport mechanisms for drug absorption?

  • Carrier Mediated Transport
  • Paracellular Transport
  • Transcellular Transport
  • Passive Diffusion
  • Endocytic Process
• What is the primary mechanism for passive diffusion?

  Occurs down a concentration gradient
• What factors influence transcellular passive diffusion?

  Lipid solubility and degree of ionization
• What is the role of partitioning in drug absorption?

  Facilitates diffusion across lipid membranes
• What does a positive Log P indicate about a drug?

  It is more oil soluble
• What is the significance of pKa in drug absorption?

  It determines the extent of ionization
• How does pH affect the absorption of weak acids and bases?

  Weak acids are better absorbed in low pH
• Why are weak acids well absorbed in the stomach?

  Because they are mainly unionized at low pH
• What are the limitations of the pH-partition hypothesis?

  • Weak acids can be absorbed in the intestine
  • Microenvironment pH differs from bulk pH
  • Certain drugs are absorbed despite being ionized
• What is Lipinski's rule of 5 regarding drug absorption?

  No more than 5 H-bond donors
• What are the two factors influencing bioavailability?

  Dissolution rate and permeation rate
• What is the major route of absorption for most drugs?

  Transcellular passive diffusion
• What does bioavailability depend on?

  Properties of the drug
• What must a drug cross to be absorbed?

  The epithelium
• What factors limit drug absorption according to chemical properties?

  Too many H-bonds and large molecular size
• What dictates permeability in drug absorption?

  Apical membranes composed of lipids and proteins
• What are the types of transport mechanisms for drug absorption?

  • Carrier mediated transport
  • Paracellular transport
  • Transcellular transport
  • Passive diffusion
  • Endocytic process
• What are the routes of drug absorption summarized?

  • Passive diffusion: Transcellular for small lipophilic molecules
  • Paracellular for small hydrophilic molecules
  • Carrier-mediated and transcytosis for larger molecules
• What is passive diffusion in drug absorption?

  Movement down a concentration gradient
• What factors influence transcellular passive diffusion?

  Lipid solubility and degree of ionization
• What does the Biopharmaceutics Classification System (BCS) classify drugs based on?

  Aqueous solubility and intestinal permeability
• What factors influence paracellular passive diffusion?

  Molecular size
• What is the role of partitioning in drug absorption?

  Diffusion across lipid membrane
• What defines high solubility in the BCS?

  Soluble in 250 mL or less of aqueous media
• What is the significance of the partition coefficient?

  Reflects drug transfer between phases
• What does a Log P value greater than 0 indicate?

  Drug is more oil soluble
• What percentage of the administered dose indicates high permeability in the BCS?

  85% or more
• How is Log P calculated?

  By shaking octanol and water mixtures
• What happens to unionized drugs in terms of absorption?

  They have higher lipid solubility
• What is the significance of the BCS in drug formulation?

  • Informs dosage form design
  • Helps predict drug absorption
  • Classifies drugs for regulatory purposes
• What is the pKa of aspirin?

  3.0
• At what pH is aspirin mainly unionized?

  pH 1.2
• Why are weak acids well absorbed in the stomach?

  Because they are mainly unionized
• What is the limitation of the pH-partition hypothesis?

  Weak acids can be absorbed in the intestine
• What is the major route of oral absorption?

  Transcellular passive diffusion
• What are Lipinski's rule of 5 criteria for drug absorption?

  • No more than 5 H-bond donors
  • No more than 10 H-bond acceptors
  • Molecular weight less than 500 daltons
  • Log P less than 5
• What is the implication of the ratio of protein to lipid in plasma membranes?

  It indicates complexity in drug transport
• What are the routes of drug absorption summarized?

  • Passive diffusion: Transcellular for small lipophilic molecules
  • Paracellular for small hydrophilic molecules
  • Carrier-mediated and transcytosis for larger molecules