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Pharmacology & Anesthesiology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

what are the 4 main pharmacokinetic processes

A

1) absorption
2) distribution
3) metabolism
4) excretion

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2
Q

what is absorption

A

movement of the drug into systemic circulation

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3
Q

what is bioavailability

A

fraction of administered drug that reaches the systemic circulation unchanged

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4
Q

what route is associated with the highest and the lowest bioavailability

A

highest: IV (100%)
lowest: oral

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5
Q

If 70% of buprenorphine is metabolized by the liver in one pass, what is the oral bioavailability?

A

30%

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6
Q

the most rapid absorption is associated with what route

A

IV (essentially instantaneous)

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7
Q

faster absorption is associated with ___________ effect and _________ duration, whereas slower absorption is associated with _______________ effect and _________ duration

A

faster absorption is associated with stronger effect and shorter duration

slower absorption is associated with smaller effect and longer duration

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8
Q

what is the risk if absorption is too slow

A

may not reach MEC for desired effect (drug is being eliminated as it is being absorbed)

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9
Q

what are the two classifications of administration and what is the difference

A

enteral (goes through liver before entering systemic circulation) and parenteral (does not pass through liver before entering systemic circulation)

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10
Q

classify oral, IM, IV, and SQ as either parenteral or enteral

A

Enteral: oral
Parenteral: IV, IM, SQ

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11
Q

what is always a concern with oral drugs

A

emesis and GI irritation possible, so the drug may never reach the MEC due to vomiting

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12
Q

is sublingual route enteral or parenteral

A

parenteral (it is absorbed across the oral mucosa into the systemic circulation)

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13
Q

what type of drugs is SQ good for

A

insoluble, oily, or solid pellets (note: should not be chemically irritating)

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14
Q

how could you slow the absorption of an IM drug

A

form an oily suspension

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15
Q

what type of administration is suitable for large volumes of drugs

A

IV bolus injection

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16
Q

what is a major drawback of IV administration

A

need to administer slowly to prevent cardiac toxicity

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17
Q

what is the safest route of administration of irritating drugs

A

IV CRI

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18
Q

if you needed to deliver a drug to a specific site (ex. the testes) in high concentrations, what route of administration would you choose

A

topical

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19
Q

what is the difference between topical and transdermal

A

transdermal is absorbed into the systemic circulation from the skin to have actions elsewhere in the body; topical is meant to be absorbed and act on the site of administration

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20
Q

in what form is a drug more easily absorbed and what would this form be for a weak acid and weak base

A

more easily absorbed in unionized form (lipid soluble form); AH or B

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21
Q

in what form is a drug more easily excreted and what would this form be for a weak acid and weak base

A

ionized form (water soluble form); A- or BH+

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22
Q

Will a weakly acidic drug with a pKa of 4.4 be better absorbed from the stomach (pH = 1.4) or small intestine (pH = 6.4)?

A

stomach (because it will be in its unionized form, AH)

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23
Q

A weakly basic drug with a pKa of 8.4 is administered orally. Will it be better absorbed from the stomach (pH = 2.4) or small intestine (pH = 6.4)

A

small intestine (because more will be in its unionized form, B)

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24
Q

Assuming you want to maximize absorption, would most oral drugs be weak acids or weak bases?

A

weak acids

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25
Q

Do drugs accumulate on the side of the membrane where ionization is highest or lowest?

A

highest (aka BH+ or A-)

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26
Q

Will a base accumulate in an environment that is more acidic or more basic?

A

It will accumulate where it is BH+ therefore acidic

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27
Q

Will an acid accumulate in an environment that is more acidic or more basic?

A

It will accumulate where it is A- therefore basic

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28
Q

What is distribution

A

movement of the drug from systemic circulation into other tissues

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29
Q

what is the distribution pathway

A

blood plasma -> extracellular fluid -> cells

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30
Q

T/F only a small fraction of each dose reaches the target receptor sites

A

true (the rest accumulates where it isn’t needed or is excreted before it reaches target receptors)

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31
Q

what 4 factors influence drug distribution

A

1) physiochemical properties of the drug
2) anatomy and physiology of the animal
3) plasma protein binding
4) tissue drug binding

32
Q

once a drug enters blood, how long does it take to distribute to the entire blood volume

A

1-2 minutes

33
Q

in the short term, tissues that ____________ receive more drug; in the long term, tissues that _______________ receive drug as equilibrium between occurs

A

have higher blood flow; are larger but less well-perfused

34
Q

what types of drugs enter the BBB well

A

highly lipid soluble and low protein-binding

35
Q

T/F protein bound drug will not be distributed to tissues to produce the effect and instead will be excreted

A

F; they will not be able to enter tissues to produce a desired effect, but they will also not be excreted

36
Q

what is the consequence of plasma protein binding on half-life and drug intensity

A

increases half-life but decreases intensity of effect

37
Q

T/F protein/drug binding is a nonlinear, saturable process

A

T

38
Q

The local anesthetic lidocaine is a weak base. It must diffuse into neurons to reach its target receptors. If infected tissue is more acidic than healthy tissue, would you expect lidocaine to be more or less effective in infected tissue.

A

Less effective.

Rationale:
1) to diffuse into tissues, lidocaine needs to be in its unionized form (aka B)
2) in an acidic environment, lidocaine will be in the BH+ form, which is ionized

39
Q

Explain: Mepivacaine is a weak base used for equine nerve blocks that diffuses better in tissues than other local anesthetics because it has a lower pKa

A

pH is greater than pKa - favours the B form, which makes it easier to diffuse into tissues

40
Q

From a pharmacokinetic point of view, what are the two compartments of the body

A

1) vascular compartment
2) everything else

41
Q

a higher Vd indicates

A

more drug has left the bloodstream and entered tissues

42
Q

if some drug has been distributed to other tissues, Vd will be ____________ than blood volume

A

greater

43
Q

how do we express Vd

A

L/kg BW or mL/kg BW

44
Q

drugs with a small Vd may require _________ doses to be effective

A

larger

45
Q

drugs with a large Vd may take _______ time to excrete

A

longer (the drug needs to be in the blood to be delivered to an organ of elimination)

46
Q

You would expect a water-soluble (ionized) drug to have a ________ Vd, whereas you would expect a lipid-soluble (unionized) drug to have a ___________ Vd

A

small to intermediate; high

47
Q

What would be more readily excreted in the urine, a drug with a pKa of 7.4 that is a weak acid or a weak base? Assume blood pH = 7.4 and urine pH = 5.4

A

weak base; want it to be in its ionized form in the urine (BH+ vs AH)

48
Q

What is another word for metabolism

A

biotransformation

49
Q

define metabolism

A

any chemical change made to a drug from the body

50
Q

what are the two goals of metabolism and what is the exception?

A

1) make drug more water soluble
2) make drug inactivated

Exception: pro-drugs that must be metabolized into their active form

51
Q

what is the main location of drug metabolism

A

liver

52
Q

what are phase I reactions? what are phase II reactions?

A

phase 1: non-synthetic “functionalization”
phase 2: biosynthetic “conjugation”

53
Q

phase I reactions inactivate drugs mainly by what mechanism

A

oxidation

54
Q

in comparison to the parent molecule, phase 1 metabolites are usually more (2)

A

water-soluble and chemically reactive

55
Q

phase II metabolites are usually (3)

A

polar, inactive and readily excreted

56
Q

what dietary component of phase II metabolism are cats deficient in

A

glucuronic acid

57
Q

cats are deficient in many transferases for phase II metabolism, which has what consequence

A

they have difficulty metabolizing many drugs and they therefore reach higher concentrations and have longer duration of action

58
Q

what is the normal process of acetaminophen metabolism and how does this differ in the case of toxicity

A

normally: undergoes phase II metabolism by conjugation to glucuronic acid or sulphate
overdose: conjugation pathways overwhelmed -> metabolized via phase I metabolism by P450 enzymes into highly reactive NAPQI -> liver failure

59
Q

you have a cat present with acetaminophen toxicity - what is your first step?

A

administer a source of glutathione -> get the phase II conjugation pathways working again

60
Q

what are 6 factors that impact the rate of drug metabolism

A

1) enzyme induction and inhibition
2) multidrug therapy
3) distribution
4) age
5) genetics
6) disease

61
Q

A food/drug constituent increases the activity of a hepatic enzyme. What effect will this have on drug action and rate of drug metabolism?

A

decreases the drug action by increasing the rate of drug metabolism

62
Q

what are the organs involved in elimination

A

kidney, liver, lungs, intestinal tract, other (sweat, milk, tears)

63
Q

T/F glomerular filtration is a non-saturable and non-selective process

A

T

64
Q

a constant ________ of drug in the body is eliminated per unit tme

A

fraction

65
Q

after how many half-lives have we essentially eliminated all of the drug

A

4-5

66
Q

what is steady state

A

when plasma concentration of drug varies between two set levels without any accumulation

67
Q

steady state is achieved within how many half-lives for any regular dosing regimen

A

5

68
Q

why is a steady state reached and the plasma concentration doesn’t continually go up

A

kidneys filter a constant fraction of drug per time; a situation is reached within the dosing regimen where the amount administered per dose is equal to the amount cleared by the kidneys, so the values stabilize

69
Q

how do we minimize fluctuations in drug concentration

A

giving small doses frequently (ex. a CRI)

70
Q

if rate of drug administration is doubled, what happens to the steady state drug concentration, Css

A

doubles

71
Q

how can you reach Css instantly

A

give a loading dose, wait 1 half-life and then give normal dose

72
Q

In the case of renal failure, what happens to drug half life and why

A

increases, because the rate of excretion decreases

73
Q

how are some drugs excreted by the liver

A

undergoing phase II metabolism followed by active excretion into bile -> into gut -> eliminated in feces

74
Q

T/F enterohepatic recycling depends on route of administration

A

F; just depends on secretion of the drug into the bile

75
Q

what is drug response proportional to

A

concentration of free drug at the target organ

76
Q

how do we express clearance

A

volume (because it will not change based on the concentration of drug)

Pharmacology & Anesthesiology (12 decks)

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