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Pharmaceutics 2 Winter Final > 1 - Intro to Biopharmaceutics > Flashcards

1 - Intro to Biopharmaceutics Flashcards

1
Q

What is a membrane? How thick is it? How is it arranged?

A
  • Phospholipid bilayer
  • 10 nm thick
  • Arranged w/ hydrophilic heads on outside and lipophilic chains facing inwards
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2
Q

What is attached to a membrane? Are they attached to the outer or inner side?

A
  • Glycoproteins (protein w/ carbohydrate attached), which may act as ion channels, receptors, intermediate messengers (G-proteins), or enzymes
  • Can be attached to outer or inner sides
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3
Q

Is the structure of a membrane the same in every tissue?

A

No, it changes to allow more specialized functions

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4
Q

Describe the membranes found in capillary endothelial cells

A

Have regions where outer and inner membranes are fused together (called fenestrae) to increase permeability, especially to fluid

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5
Q

Describe the membranes of renal glomerular endothelium

A

Has gaps between cells to allow passage of larger molecules as part of filtration

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6
Q

Describe the membranes of the blood brain barrier

A

Tight junctions between endothelial cells of brain blood vessels to form the BBB and limit passage of polar molecules

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7
Q

What are the methods to cross a cell membrane?

A
  • Active transport using energy (ATP hydrolysis) – usually specific for endogenous molecules, often transports molecules against a concentration gradient
  • Passive transport – most common mode of drug passage through membranes; involves diffusion
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8
Q

What is another name for passive transport across a cell membrane?

A

Transcellular diffusion

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9
Q

What determines the rate of passive diffusion?

A
  • Partition coefficient of the compound
  • Diffusion coefficient of the compound
  • Concentration gradient across the membrane
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10
Q

What are some important chemical properties for membrane binding and diffusion? What other process are these important for?

A
  • Lipophilicity
  • Molecular weight (lower MW is better)
  • Molecular polarity
  • Also important for facilitated transport where a protein channel helps diffusion but doesn’t need energy
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11
Q

What is partition coefficient?

A

How the drug partitions between water and lipid

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12
Q

Which drugs can cross membranes using paracellular transport? (Which chemical properties)

A
  • More hydrophilic
  • Water soluble
  • Low to intermediate molecular weight
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13
Q

Unionized drugs are ___ soluble

A

Lipid

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14
Q

What determines the rate of drug transfer across a lipid bilayer?

A
  • pKa of the drug

- Fraction in the unionized form

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15
Q

What are some factors that influence rate of diffusion?

A
  • Concentration gradient
  • Ionization
  • Lipid solubility
  • Protein binding
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16
Q

What is Fick’s law?

A

Rate of transfer is proportional to the concentration gradient across a membrane

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17
Q

What are some factors that determine the rate of transfer across a concentration gradient?

A
  • Membrane area
  • Concentrations on either side of the membrane
  • Diffusion constant
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18
Q

What determines the diffusion constant?

A

Lipid solubility and molecular weight of the compound

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19
Q

The ____ the molecule, the easier the transfer across a membrane

A

Smaller

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20
Q

What determines degree of ionization of a drug?

A

pKa of drug and pH of environment

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21
Q

What is ion trapping?

A

The rule that an acidic drug will accumulate on the more basic side of a membrane and a basic drug on the more acidic side

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22
Q

Lipid solubility allows a drug to pass through a cell membrane using the ____ pathway

A

Transcellular

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23
Q

Which portion of ADME does lipid solubility affect?

A

Absorption

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24
Q

A molecule w/ a _____ will be permanently ionized

A

Quaternary ammonium

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25
Will a very lipophilic molecule w/ poor water solubility have good or bad absorption? Why?
Poor b/c water solubility is the limiting factor in absorption
26
Can protein bound drugs cross a membrane? What does this mean?
- No, only unbound can cross - Increasing plasma concentration of unbound drug will increase rate of transfer across a membrane and accelerate onset of action
27
Which proteins bind to drugs? What can alter the amount of protein binding?
- Albumin and globulins - Protein binding altered in pathological conditions - Albumin concentration drops during inflammation
28
What is the biopharmaceutics classification system (BCS)?
Framework for classifying drug substances based on aqueous solubility and intestinal permeability
29
Which drugs are included in the BCS? What factors are considered?
- Immediate release oral dosage forms | - Dissolution, solubility, and intestinal permeability determining rate and extent of oral absorption
30
What are the 4 classes of the BCS?
- Class 1 = highly soluble and highly permeable - Class 2 = poorly soluble and highly permeable - Class 3 = highly soluble and poorly permeable - Class 4 = poorly soluble and poorly permeable
31
When is a drug considered highly soluble in the BCS?
When the highest dose is soluble in 250 mL of aqueous media over the pH range of the GI tract (1.2-7.4)
32
When is a drug considered highly permeable in the BCS?
When absorption (including liver and intestinal first pass metabolism) equals or exceeds 85% of administered dose
33
What is dose solubility volume (DSV)?
The highest therapeutic dose (in mg) divided by the solubility of the substance in mg/mL at a given pH and temperature
34
What DSV will allow a drug to be considered highly soluble?
DSV equal or less than 250 mL
35
What is a biowaiver? Which classes of drugs can be issued a biowaiver?
- Issued by Health Canada, allows a generic drug to be marketed w/o performing an in vivo bioequivalence study - For class 1 or class 3 immediate release oral dose forms
36
What are some rules for biowaivers?
- Sublingual or buccal products not eligible - Test and reference product must be the same - If coated, must be a non-functional coating (can't be enteric coated)
37
What are the required conditions for dissolution for bioequivalence?
- Basket (USP 1) or paddle (USP 2) apparatus - Basket at 100 rpm; paddle at 50 rpm - Dissolution mediate are aqueous buffers at pH 1.2, 4.5, and 6.8 - Dissolution media volume equal or greater than 900 mL - Sampling times 5, 10, 15, 20, and 30 minutes - Temperature 37 C +/- 1 C and not less than 12 units per pH medium
38
What is the accepted dissolution result for a class 3 substance?
More than 85% dissolved in 15 minutes or less
39
What is the accepted dissolution result for a class 1 substance?
- If very fast dissolving, more than 85% dissolved in 15 minutes or less - For all others, more than 85% dissolved in 30 minutes or less
40
What is F2 testing? What is an accepted F2 value?
- F2 = similarity factor - Measurement of the similarity in the percentage dissolution between the 2 curves - Must be between 50 and 100
41
Most bioavailability studies involve drug measurement in _____ or _____
Blood or urine
42
What is assumed when measuring bioavailability?
That the drug at the site of action is in equilibrium w/ the quantity of drug in the blood, so blood level is an indirect measure of drug response
43
What is bioavailability?
Measure of how much and how quickly drug appears in the blood after administration
44
What can be done to increase onset of action of a drug?
Use a dose form allowing rapid absorption and high serum levels
45
When would a slower rate of absorption be desirable?
When high serum levels are associated w/ toxicity
46
What is absolute bioavailability?
Fraction of dose that reaches the bloodstream
47
What is the range for absolute bioavailability?
- 0-1 - 0 = no drug is absorbed - 1 = entire administered dose reaches the blood
48
What is the total amount of drug reaching the bloodstream proportional to?
AUC
49
How is absolute bioavailability calculated?
- Comparison of AUC of oral test product to AUC of dose given intravenously - If doses differ, respective AUC values are divided by respective dose
50
What is relative / comparative bioavailability?
- The bioavailability of a test product to a reference standard of the same drug usually at the same dose - Determines effects of formulation differences on extent and rate of absorption
51
What are some factors that affect bioavailability?
- Route of administration - Formulation factors - Physicochemical nature of drug or excipients (if they affect dissolution rate) - Px factors
52
Any factor which affects ____ will affect bioavailability
Dissolution or absorption
53
Rank the oral dose forms from fastest to slowest availability
- Solutions - Suspensions - Capsules - Tablets - Coated tablets - Controlled-release tablets
54
What can affect dissolution rate?
- Particle size - Crystalline structure - Salt or ester form of drug - Formulation factors (disintegrants, binders, lubricants, coatings)
55
Which part of ADME does local blood flow affect? Why?
- Absorption rate | - Blood flow continuously maintains concentration gradient needed for passive diffusion across membranes
56
Does first pass metabolism only occur in the liver?
No, can also occur in intestines and lungs
57
What does extraction ratio measure?
The effect of first pass hepatic metabolism on bioavailability
58
Which meals are most likely to affect GI physiology? What does this mean?
- Meals high in total calories and fat content | - They affect bioavailability also
59
What effect does metoclopramide have on absorption of other drugs?
- Stimulates stomach contraction and generally increases intestinal peristalsis - May reduce residence time and Cmax and increase Tmax
60
Which drugs can complex w/ aluminum, calcium, or magensium?
Tetracycline and ciprofloxacin
61
A drug w/ poor bioavailability has one or more of the following...
- Poor aqueous solubility - Slow dissolution rate in biological fluids - Poor stability under physiological conditions - Poor permeation through biological membranes - Extensive first pass metabolism
62
What are 3 approaches to enhance bioavailability?
- Biological where route of administration or dosage form is changed - Chemical modification to increase solubility or permeability (often through formation of pro-drug) - Pharmaceutical where formulation is modified, usually to enhance rate and extent of dissolution
63
What is a typical size range of particles?
2-5 um
64
When is complexation a useful solubilization technique? Complexation w/ which drug? What is the most common form
Complexation w/ cyclodextrins (common form is 1:1 ratio) is useful for drugs w/ lipophilic properties
65
Which class of drugs will have an effect on bioavailability when complexed w/ cyclodextrin?
Class 2 and 4 drugs

Pharmaceutics 2 Winter Final (9 decks)

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