PHRD5925 Pharmaceutics Lecture 12 - Drug Absorption (Part 2)

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daynuhmay
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PHRD5925 Pharmaceutics Lecture 12 - Drug Absorption (Part 2)
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2014-04-20 21:29:15
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Drug Absorption
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Drug Absorption
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  1. 3 main pharmaceutical factors affecting drug absorption
    • 1) disintegration
    • 2) dissolution
    • 3) permeability
  2. relates the flux (rate) to the concentration gradient under steady state conditions
    Fick's First Law
  3. Fick's First Law (eqn)


    diffusion rate = diffusion coefficient * concentration gradient across the boundary
  4. predicts how diffusion causes the concentration to change with time
    Fick's Second Law (second derivative)
  5. 3 parameters permeability is depedent on
    • 1) partition coefficient
    • 2) diffusion coefficient
    • 3) thickness/area of the membrane
  6. permeability (eqn)
    P=DK/h

    permeability coefficient = (diffusion coefficient * partition coefficient) / membrane thickness
  7. dW/dt
    diffusion rate
  8. process by which a solid enters into a solution
    dissolution
  9. parameters dissolution rate is dependent on (4)
    • 1) time
    • 2) particle size
    • 3) solubility
    • 4) formulation factors
  10. equation that determines rate of dissolution based on the change in concentration over time

    (rapid formation of diffusion layer followed by slow dissolving step)
    Noyes-Whitney
  11. equation that determines rate of dissolution based on change in the amount of solid drug over time
    Nernst-Brunner
  12. equation that determines how the radius of the drug/mass changes as the particle dissolves

    (takes into account the change in particle size during dissolution)
    Hixon-Crowll Cube Root Law
  13. 2 factors affecting dissolution
    • 1) particle size/surface area of drug particles
    • 2) solubility of a drug (salt vs nonsalt, crystalline vs amorphous)
  14. 3 ways to increase surface area
    • 1) micronization
    • 2) nanocrystallization
    • 3) mortar & pestle
  15. sodium & potassium salts dissolve _____ than the free acid
    faster
  16. amorphous solids have ____ solubility compared to crystalline solids
    higher
  17. ability of solid material to exist in more than 1 crystal form
    polymorphism
  18. only 1 form is stable under a given set of conditions. all other forms are _____.
    metastable
  19. the stable crystalline form has _____ solubility than the metastable form.
    lower
  20. fraction of dosage form that reaches the site of action or biological fluid from which the drug has access to its site of action
    OR
    rate/extent to which the active ingredient is absorbed from a drug product & becomes available at the site of action
    bioavailability (BA)
  21. 4 factors bioavailability is dependent on
    • 1) biopharm properties (dissolution/permeability)
    • 2) physicochemical properties 
    • 3) stability of drug in GIT
    • 4) 1st pass metabolism
  22. the absence of significant difference in the rate and extent of the bioavailability of the API in 2 formulations administered under similar conditions
    bioequivalence (BE)
  23. API
    active pharmaceutical ingredient
  24. BCS is based on...
    solubility & permeability
  25. 3 criteria that must be met for BCS to be used
    • 1) solubility
    • 2) permeability
    • 3) dissolution
  26. high solubility =
    highest dosage strength is soluble in 250mL aqueous media over pH range 1.2-6.8
  27. high permeability =
    extent of absorption in humans 90% of the administered dose
  28. BCS Class I
    • high solubility
    • high permeability
  29. BCS Class II
    • low solubility
    • high permeability
  30. BCS Class III
    • high solubility
    • low permeability
  31. BCS Class IV
    • low solubility
    • low permeability
  32. criteria for rapid dissolution, per the Dissolution Test
    >85% in <30min in pH 1.2, 4.5, 6.8
  33. Criteria to be granted a biowaiver
    • 1) immediate-release
    • 2) BCS Class I

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