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PharmSci ADME > Distribution > Flashcards

Distribution Flashcards

1
Q

How many L in human is intracellular water?

A

27L

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2
Q

How many L in human is extracellular water?

A

15L

  • plasma 3L
  • interstitial water: 12L
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3
Q

How many L in humans is in blood?

A

5L

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4
Q

Pathway of drug molecules

A
  • carried by blood –> capillaries
  • to tissue with interstitial fluid (extracellular water)
  • diffuse across cell membrane into cytoplasm (intracellular water)
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5
Q

The passage of drug molecules across a cell membrane depends on what?

A

drug and cell membrane

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6
Q

T/F hydrophilic drugs generally diffuse across cell membranes more easily than hydrophobic drugs

A

FALSE!

hydrophobic diffuse more easily

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7
Q

T/F small drug molecules diffuse more rapidly across cell membranes than large drug molecules

A

True

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8
Q

T/F if a drug is bound to a plasma protein, the drug protein complex becomes too large for easy diffusion

A

True

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9
Q

What is the primary driving force for fluid transport in the body?

A

hydrostatic pressure

- pressure b/t arterial end of capillaries entering the tissue and venous capillaries leaving tissue

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10
Q

Is hydrostatic pressure higher in arteries or veins?

A

higher in arteries (+10mmHg)

lower in veins (-7mmHg)

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11
Q

Define capillary hydrostatic pressure (CHP)

A
  • pressure exerted by blood against the capillary wall

- drives fluid into tissues

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12
Q

Define interstitial fluid hydrostatic pressure (IFHP)

A

pressure exerted on capillary from interstitial fluid

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13
Q

T/F arterial CHP is considerably higher than IFHP

A

True

because of absorption of fluids by lymphatic vessels

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14
Q

Define osmotic pressure

A
  • net pressure that drives the movement of fluid from interstitial space back into the capillaries
  • works against blood pressure
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15
Q

Define blood colloidal osmotic pressure (BCOP)

A
  • pressure created by the concentration of colloidal proteins in the blood
  • higher protein concentration = higher BCOP
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16
Q

T/F BCOP is always lower than the interstitial fluid colloidal osmotic pressure

A

FALSE

  • always higher because interstitial fluid contains few proteins
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17
Q

Define net filtration pressure (NFP)

A

difference between CHP and BCOP

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18
Q

If a drug diffuses rapidly across the membrane in such a way that blood flow is the rate limiting step –>

A

perfusion/flow limited

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19
Q

If a drug distribution is limited by the slow diffusion of drug across the membrane in the tissue —>

A

diffusion/permeation limited

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20
Q

T/F distribution proceeds more slowly for polar drugs than for lipophilic drugs

A

true

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21
Q

The time for drug distribution is generally measured by what?

A

distribution half life td1/2

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22
Q

Q

A

blood flow to organ

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23
Q

V

A

volume of organ

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24
Q

kd related to?

A

perfusion

25
Q

td1/2 equation

A

0.693/kd

26
Q

kd equation

A

(Q/V)/R

27
Q

If each tissue has the same R, then td1/2 is determined by what?

A

Q & V

28
Q

Increasing Q leads to ______ distribution time

A

decreased

29
Q

increasing V leads to ______ distribution time

A

increased

30
Q

How can we measure the [drug] in the body fluids?

A

volume of distribution (Vd)

31
Q

Define Vd

A

parameter that quantifies the extent to which a drug is distributed outside the systemic circulation

32
Q

High R related to distribution & elimination

A

longer for both

33
Q

the deposit/uptake of the drug is controlled by what?

A

diffusion barrier of the capillary membrane

34
Q

The accumulation of drugs in the tissue is dependent on what?

A

blood flow

affinity of drug for tissue

35
Q

Affinity to tissues may be due to what?

A
  • solubility and pH trapping
  • binding to tissue proteins
  • low binding to plasma proteins
  • chelation
  • active transport
  • complexation with cellular DNA
36
Q

T/F Vd is not a physiological volume in the body

A

true!

hypothetical

37
Q

Vd equation

A

amount (mg) of drug in system/drug conc (mg/L) in system after equilibrium

38
Q

The tissue drug concentration is influenced by what?

A

partition coefficient

tissue protein binding

39
Q

Drugs with high Vd have _____ tissue affinity or _____ binding to serum albumin

A

high

low

40
Q

What types of drugs have a Vd similar to the volume of extracellular water?

A

polar or hydrophilic

41
Q

T/F drug protein binding is reversible

A

can be reversible or irreversible

42
Q

Irreversible drug protein binding is usually a result of what?

A

metabolic activation

can lead to drug toxicity

43
Q

Why are protein bound drugs more restricted to distribution?

A

large size

do not diffuse freely

44
Q

Only the __ drug is available for ADME and to produce pharmacological effect

A

free

45
Q

Albumin is _% of plasma proteins

A

50%

- acidic (anionic) xenobiotics

46
Q

AAG binding

A

basic (cationic) xenobiotics

47
Q

What are the determinants of protein binding?

A
  • drug
  • protein
  • affinity between drug and protein
  • drug interactions
  • pathophysiologic condition of patient
48
Q

Drug determinants of protein binding

A

physicochemical properties

total concentration in body

49
Q

protein determinants of protein binding

A

quantity of protein available for drug binding

quality of protein

50
Q

drug interactions as determinant of protein binding

A
  • competition for drug by other substances

- alteration of protein by a substance that modifies the affinity of the drug for protein

51
Q

T/F at stead state, unbound drug in plasma and tissue are in equilibrium

A

True

Cu = Cut

52
Q

What compound can be used to estimate plasma Vd?

A

evans blue

53
Q

What compound can be used to estimate extracellular fluid?

A

Br

54
Q

What compound can be used to estimate total body water?

A

ethanol

55
Q

Drugs with low plasma protein binding have a _______ fraction of unbound drug (fu)

A

larger
diffuse more easily into tissues

larger Vd

56
Q

Displacement of drugs from plasma proteins affect on Pk

increase Fu concentration

A
  • directly as result of reduced binding in blood
  • reaches receptor sites directly, cause more therapeutic (or toxic) response
  • cause transient increase in Vd
  • result in more drug diffusion into tissue of eliminating organs –> transient increase in drug elimination
57
Q

In general, drugs that are highly bound to plasma proteins have _____ overall drug clearance

A

reduced

58
Q

relationship between Vd and drug elimination

A

k = Cl/Vd

59
Q

Low plasma drug concentration may be due to what?

A
  • extensive distribution into tissues due to favorable lipophilicity
  • extensive distribution into tissues due to protein binding
  • lack of drug plasma protein binding

PharmSci ADME (4 decks)

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