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Physiology > L8, L9 Pharmacokinetics > Flashcards

L8, L9 Pharmacokinetics Flashcards

1
Q

What makes up pharmacokinetics?

A

drug absorption
drug distribution
drug metabolism
drug excretion

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2
Q

drug in circulation will be at ______ with tissue reservoirs?

A

equilbrium

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3
Q

only a fraction of drug that binds to specific receptors will have a ____

A

pharmacological effect

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4
Q

how does the drug get to the site of action?

A
  • crosses membrane
  • gets into systemic circulation or lymph system
  • needs to workout how best to get the drug into circulation
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5
Q

what is the first barrier to oral administration of drugs?

A

GI epithelium

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6
Q

what is membrane diffusion favored by?

A

concentration gradient - high

+ change on drug (inside of cell is -)

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7
Q

what does the pKa represent?

A

pH value when 1/2 of the drug in protonated and half deprotonated

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8
Q

what is pH trapping

A

for weakly acidic drugs, the protonated, electrically neutral drug is predom. in the highly acidic environment of the stomach. the uncharged drug can pass through lipid bilayers of GI mucosa. the weakly acidic drug is then trapped as it is deprotonated to its electrically charged form in the more basic environment of the plasma.

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9
Q

what is the version of Henderson Hasselablch equation that I will use?

A

Pka - pH = log [HA]/[A-]

HA protonated form
A- deprotonated form

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10
Q

a weakly acidic drug in an acidic enviromment will ne ?

A

protonated - neutral

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11
Q

a weakly acidic drug in an basic or neutral environment will be?

A

deprotonated - charged

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12
Q

what is pKa

A

acid dissociation constant

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13
Q

if the pH < pKa -

A

protonated form favored (HA, BH+)

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14
Q

if pH > pKa -

A

unprotonated form favored ( A-, B)

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15
Q

define absorption

A

getting drug into circulation

bioavailability

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16
Q

what is bioavilability

A

drug reaching circulation / drug administered

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17
Q

what are routes of administration?

A

enteral - oral, by mouth
parenteral - directly to circulation, CSF etc. using SC, IM, IV, IA, IT (intrathecal)
mucous membrane - sublingual, nasal, rectal etc.
transdermal - nicotine patch, androgel etc.

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18
Q

what are the advantages of enteral drug administration?

A

simple
cheap
self-administer
low infection rate

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19
Q

what are the disadvantages of the enteral administration drug route?

A

passes through GIT
first pass metabolism
relatively slow delivery

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20
Q

which drugs pass through the cell membrane more efficiently?

A

hydrophobic and neutral drugs

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21
Q

what is first pass metabolism?

A

after drugs pass GI epithelium they are carried by the portal system to the liver before entering systemic circulation. With this process, liver enzymes may inactivate a fraction of the ingested drug

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22
Q

what are the advantages of parenteral drug administration?

A

rapid onset

high bioavailability

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23
Q

what are the disadvantages of parenteral drug administration?

A

infection
need skilled personal for delivery
hurts
irreversible effect

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24
Q

what is the fastest way to get a drug to target organ?

A

IV, IA or intrathecal

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25
Q

for drugs that are soluble in oil-based solutions what parenteral route should I use?

A

IM

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26
Q

what are advantages of mucous membrane drug administration?

A 
DIRECT ACTION
rapid absorption
low infection incidence
convenient 
no harsh GI environment + first pass metabolism
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27
Q

mucous membranes are highly vascular and drugs enter ____ into the systemic circulation

A

directly

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28
Q

what is atropine?

A

from Atropa belladonna - Deadly nightshade
counters “rest and digest” form PNS
competitive antagonist of muscarinic receptor
it dilates pupil, increase heart rate, reduces salivation

29
Q

in order for a drug to pass transdermally, what should the drug be?

A

highly lipophilic - nicotine or estrogen patches

30
Q

what is transdermal administration ideal for?

A

drugs that must be slowly and continuously administered over extended periods of time

31
Q

what are the benefits of transdermal drug administration?

A
  • no infection risk
  • simple
  • convenient
32
Q

what is the rate of absorption affected by?

A

local, regional and systemic factors

33
Q

what has the greatest effect on absorption?

A

regional blood flow

34
Q

the rate of absorption affects what?

A
  • local concentration of the drug

- duration of action

35
Q

what primarily achieves drug distribution? what plays a minor role in drug distribution?

A

circulatory system

lymphatic system

36
Q

once the drug hits systemic circulation, it is able to go where?

A

to any target organ - except brain and testes…

37
Q

what is used to define and monitor therapeutic drug levels?

A

concentration of drug in plasma

38
Q

what is the volume of distribution?

A

extent to which the drug partitions between the plasma and the tissue compartments

its the fluid volume that would be required to contain the total amount of absorbed drug in the body at a concentration equivalent
to that in the plasma at steady state

39
Q

what is the equation for volume of distribution?

A

Vd = Dose / [Drug]plasma

40
Q

when are Vd low?

A

drugs that are retained within vascular compartment

41
Q

when are Vd high?

A

drugs that are highly distributed into muscle, adipose and nonvascular compartments

42
Q

a drug that is highly distributed, gives a ____ plasma concentration for a set dose

A

lower

43
Q

what is the most abundant plasma protein?

A

albumin

44
Q

drugs with high affinity for plasma proteins keep Vd ____ and free drug ___

A

low

low

45
Q

what happens to the drug concentration in the distribution phase?

A

results in sharp decrease
in the plasma drug concentration shortly after
intravenous administration of a drug bolus - because
of the drug elimination from the body

46
Q

what happens to the drug concentration during the elimination phase?

A

the plasma drug concentration decreases more
slowly during the elimination phase due to the “
reservoir” of drug in tissues that can diffuse
back into blood to replace the drug that
has been eliminated

47
Q

*The half time for drug________ is longer than the

half time for drug _____

A

elimination

distribution

48
Q

what is the first extracellular compartment where drug concentration increases?

A

vessel rich group

49
Q

which groups have a higher capacity for taking up drug than vessel rich?

A

muscle rich and adipose rich

50
Q

what group accumulates the greatest amount of drug at the slowest rate?

A

adipose rich group

51
Q

what drug character can enter liver cells?

A

hydrophobic drugs

52
Q

what can the liver do to drugs?

A
  • may make them more active

- usually become inactive and ready for excretion (biotransformation - red/ox conj/hyd)

53
Q

where are most drugs broken down?

A

liver

54
Q

where are most drugs excreted?

A

by the kidney

some in bile
some oral drugs not fully absorbed - feces

55
Q

what determines the kinetics of drug elimination by the kidney?

A

balance of filtration, secretion, and reabsorption

56
Q

what factors influence renal excretion?

A

increased urine flow

pH trapping

57
Q

how do drugs get from liver to intestines?

A

ABC transporters (ATP binding cassette)

58
Q

define clearance?

A

the amount of active drug cleared relative to the amount in plasma

59
Q

what is the equation for clearance?

A

clearance = metabolism + excretion / [drug in plasma]

clearance = clearance (by kidney + liver + anywhere else)

60
Q

what happens to the rate of drug elimination when plasma drug concentration is increased?

A

increases

*amount of drug excreted is proportional to the concentration in the plasma
E = (Vmax X C) / (Km + C)

61
Q

what happens if you saturate the mechanisms involved in clearance?

A

you no longer see first order kinetics

62
Q

what is half life?

A

the amount of time over which the drug concentration in the plasma decreases to one-half of its original value

follows first order kinetics - what I will be dealing with

63
Q

what factors increase half life?

A

decreasing clearance

  • liver, kidney, cardiac failure
  • inhibition of CY P450

increasing Vd (plasma concentration LOW)

  • major = drug properties - solubility, binding to plasma proteins, binding within compartments
  • minor = obesity, edema/ascities
64
Q

what is the therapeutic range?

A

steady state when what goes in = whats going out

65
Q

where do we want the steady state concentration to lie?

A

within the therapeutic range

66
Q

what is the loading dose?

A

allows you to get to therapeutic range quicker
takes Vd into account
huge dose one time

67
Q

what is maintenance dose?

A

dose required to maintain the drug concentration within the therapeutic range

68
Q

how many half-lifes does it take to reach a steady state concentration in the plasma?

A

4 half lives

69
Q

what happens when drug delivery beats the rate of breakdown?

A

saturation leads to zero order elimination

Physiology (16 decks)

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