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Pharmacology > EXAM #1: PHARMACOKINETICS > Flashcards

EXAM #1: PHARMACOKINETICS Flashcards

1
Q

What is absorption?

A

Movement of the agent from the site of administration into the circulation

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2
Q

What is the difference between enteral and parenteral administration?

A

Enteral= drug delivery via the GI tract

Parenteral= non-GI drug delivery

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3
Q

What are the four routes of enteral administration?

A

1) Oral
2) Sublingual
3) Buccal
4) Rectal

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4
Q

What are the pros of oral administration?

A

Highest levels of compliance

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5
Q

What is the con of oral administration?

A
  • GI tract breaks down drug
  • enters portal circulation
  • liver breaks down drug

Thus, delivery can be a challenge

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6
Q

What are the disadvantages of sublingual and buccal administration?

A

Mucosal irritation

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7
Q

What are the advantages of sublingual and buccal administration?

A

Drug is delivered directly into the venous system, BYPASSING the liver

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8
Q

What is the disadvantage to rectal administration?

A
  • Inconvenient
  • Non-compliance
  • Incomplete absorption in rectal tissue can make it difficult to predict dosing
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9
Q

What are the advantages of rectal administration?

A
  • Unconscious patients

- 50% of drug goes to liver, partially bypassing first-pass metabolism

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10
Q

What are the general cons of enteral administration?

A

1) Must pierce the skin, leading to non-compliance

2) Break in skin increases risk of infection

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11
Q

What is the advantage of IV drug administration?

A

Bypass metabolism b/c the entire dose is placed directly into the blood/ circulation

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12
Q

What is the disadvantage of IV drug administration?

A

If a mistake is made in dosing, the drug cannot be “recalled” i.e. can’t correct the mistake

*****Margin of error significantly reduced

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13
Q

What are the pros of IM & subcutaneous injections?

A
  • Dosing is less frequent

- Slow diffusion from tissuee that mirrors taking the medical regularly

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14
Q

What are the cons of IM & subcutaneous injections?

A
  • Pain that leads to poor compliance

- Especially for subcutaneous tissue, change in tissue composition with repeated administration

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15
Q

Where is an intrathecal administration delivered?

A

Subarachnoid space

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16
Q

What are the advantages of intrathecal and epidural administration?

A

Bypass the BBB and delivery of drug directly into the CNS

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17
Q

What are the disadvantages of intrathecal and epidural administration?

A

The CNS is a very delicate tissue that is prone to damage

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18
Q

What types of drugs are best given transdermally?

A

Lipophillic drugs b/c they need to pass through the lipid membrane of the epidermis

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19
Q

What is the con of transdermal drugs?

A

Skin is a difficult barrier to bypass

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20
Q

What is the pro of inhalation?

A
  • Direct administration into lungs

- Very rapid absorption

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21
Q

What are the cons of inhalation?

A

1) Irritation of lung tissue

2) Direct delivery of drug to the heart following inhalation, which is especially detrimental if the drug is cardiotoxic

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22
Q

Which form of drug is able to cross barriers, ionized or unionized?

A

Unionized

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23
Q

What form should weak acid and bases be in to best cross a lipid membrane?

A

Weak acid= protonated= unionized

Weak base= unprotonated= unionzed

Why? These forms are UNIONIZED

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24
Q

Write the Henderson-Hasselbach equation.

A

N/A

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25
Q

What is the pKa?

A

pH at which 50% if the drug is ionized, 50% is unionzed

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26
Q

If the pH is greater than pKa , what form will the drug be in?

A

pH > pKa= DEPROTONATED

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27
Q

If the pH is less than pKa, what form will the drug be in?

A

pH

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28
Q

Where is the body are weak acids and weak bases favored for absorption?

A

Stomach= low pH= protonated= weak acids more readily absorbed

Intestine= high pH= unprotonated= weak bases more readily absorbed

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29
Q

What pH favors absorption of Salicylic acid, pKa = 3?

A

Less than 3

*****Protonated and unionized

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30
Q

What pH favor absorption of Amphetamine, pKa= 10?

A

Greater than 10

*****Unprotonated and unionized

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31
Q

How much salicylic acid, pKa=3, will be absorbed from the small intestine, which has a pH of 7?

A

N/A

See ppt.

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32
Q

In the stomach (at pH=2), what is the ratio of unionized to ionized ASA?

A

N/A

See ppt.

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33
Q

At a pH of 8, what is the ratio of unionized to ionized amphetamine (pKa=10)?

A

N/A

See ppt.

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34
Q

What is the antilog of -4?

A

0.0001

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35
Q

What is the antilog of -3?

A

0.001

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36
Q

What is the antilog of -2?

A

0.01

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37
Q

What is the antilog of -1?

A

0.1

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38
Q

What is the antilog of 0?

A

1

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39
Q

What is the antilog of 1?

A

10

40
Q

What is the antilog of 2?

A

100

41
Q

What is the antilog of 3?

A

1,000

42
Q

What is the antilog of 4?

A

10,000

43
Q

What is distribution?

A

Process by which a drug leaves the circulation and enters the tissues perfused by the blood

44
Q

What are the four general factors that affect drug distribution?

A

1) Cardiovascular factors
2) Tissue binding
3) Drug molecule size
4) Lipid solubility

45
Q

What are the four cardiovascular factors that affect drug absorption?

A

1) CO
2) Regional blood flow
3) Capillary permeability
4) Binding to plasma proteins

46
Q

What is drug metabolism?

A

Biotransformation–making a drug more soluble for elimination from the body

47
Q

What is Phase I of biotransformation?

A

Generation of a more polar molecule by exposing a functional group

48
Q

What is Phase II of biotransformation?

A

Conjugation of a drug to yield a more water soluble product to be excreted

49
Q

What enzymes mediate Phase I biotransformation?

A

Cytochrome P450’s or “CYPs”

50
Q

What are the most common reactions of Phase II biotransformation?

A

Glucuronidation
Sulfation
Acetylation

Know that these are conjugation processes that are making the drugs more polar and water soluble for excretion.

51
Q

What are the key sites of biotransformation?

A 
GI 
Lungs 
Skin 
Kidneys 
Brain
52
Q

What is the “first-pass” effect?

A

Entrance into the portal circulation and initial metabolism of a drug by the liver

53
Q

What is the primary mechanism of drug elimination? Secondary?

A

Primary= renal excretion

Secondary= fecal via hepatic secretion into bile

54
Q

What are the factors that alter renal excretion of a drug?

A
  • GFR (glomerular filtration rate)
  • Binding to plasma proteins
  • Urine pH
55
Q

What is the “Volume of Distribution (V)?”

A

Measure of the space in the body available for the drug

Amount of drug in body/ Concentration of drug in blood or plasma

56
Q

What is “Clearance (CL)?”

A

Measure of the ability of the body to eliminate a drug

Rate of elimination/ concentration of drug

57
Q

Generally, what does a large V mean?

A

Greater extent to which the drug distributes to the extravascular tissue

58
Q

What does a V similar to the blood volume mean?

A

Majority of the drug is located in the vasculature

59
Q

What does a V 100x the volume of the blood mean?

A

Majority of the drug is located in the extravascular tissue e.g. fat

60
Q

What is zero-order elimination?

A

A specific amount of drug is eliminated of a specific period of time INDEPENDENT of drug concentration

E.g. 20mg of drug eliminated per 2 hours

61
Q

When is zero-order kinetics/ elimination observed?

A

When the body’s capacity to eliminate the drug is saturated

62
Q

Draw an example of zero-order elimination graphically.

A

N/A

63
Q

What is first-order elimination?

A

A constant fraction of drug is eliminated per unit time b/c the system is NOT saturated

E.g. Half the drug is eliminated from the body per 2 hours

64
Q

Draw an example of first-order elimination graphically.

A

N/A

65
Q

What is capacity-limited elimination?

A

A point at which the concentration of drug has saturated the elimination capacity of the system

Zero-order process

66
Q

What is flow-dependent elimination?

A

When the system to eliminate drug is NOT saturated, the limiting factor in elimination is how fast blood can get to the organ/system

E.g. how fast can you get blood to the liver?

67
Q

What is the consequence of continuous dosing with a drug that undergoes capacity-limited elimination?

A

Dangerous toxic levels of drug will accumulate

68
Q

What drugs are associated with capacity-limited elimination?

A

Phenytonin
ASA
Alcohol

69
Q

What drug is associated with flow limited elimination?

A

Propanolol

70
Q

What is the half-life of a drug?

A

Time required for the plasma concentration of a drug to decrease by 50%

71
Q

What is the half-life a drug dependent on?

A
  • Volume of distribution (V)

- Clearance (CL)

72
Q

After two half-lives, how much drug has been eliminated?

A

75%

73
Q

How many half-lives does it take for a drug to be “fully eliminated?”

A

4-5 half-lives

74
Q

What happens to the half-life of a drug if you reduce the clearance of the drug e.g. from renal insufficiency/failure?

A

Half-life INCREASES

75
Q

How does increasing the Volume of Distribution (V) impact the half-life of the drug?

A

Increases the half-life

76
Q

How is the initial plasma concentration calculated?

A
  • Plot drug plasma concentration vs. time (semi-log)
  • Slope= rate of elimination
  • Extrapolate the line of best fit to find the y-intercept, the Cp0

Note that Cp0= Dose/V

77
Q

What is the impact of calculating the initial plasma concentration in a one compartment vs. a two compartment model?

A
  • B/c Cp0= Dose/V, the method works well for a one compartment model with a LOW volume of distribution V
  • In the two-compartment model, Cp0 is much HIGHER than the Cp0 in a one-compartment model

If you use a one compartment model to give a loading dose, you could give a toxic/lethal initial dose

78
Q

What is an accumulation factor?

A

= 1/fraction of drug lost in one dosing interval

A factor used to predict the ratio of steady-state concentrations to the dose seen following the first dose

79
Q

When does accumulation of a drug become detectable?

A

If the dosing interval is shorter than 4 half-lives

80
Q

What is bioavailability? What is the equation for bioavailability?

A

The amount of drug that reaches the systemic circulation

F= f x (1-ER)

f= extent of absorption from gut

81
Q

What is the bioavailability of a drug given IV? How does this compare to a drug given PO?

A 
IV= 100% 
PO= much less
82
Q

What is the extraction ratio (ER)?

A

Effect of first-pass metabolism on bioavaliability

83
Q

What are the determinants of the extraction ratio?

A

ER= Hepatic Clearance/ Hepatic Blood Flow

84
Q

What is the TC?

A

Target concentration

85
Q

What is the MEC?

A

Minimum effective concentration

86
Q

What is the Css?

A

“Steady State concentration”

= Dosing Rate/Clearance

The point at which elimination of a drug is equal to the bioavaliability i.e. in and out are balanced

87
Q

How long will it take to reach the Css?

A

4-5 half-lives

88
Q

What is the therapeutic window?

A

Concentration range between the MEC for the desired effect and the MEC for the toxic effect

89
Q

If the clearance of a drug decreases from renal insufficiency or failure, what happens to the Css?

A

Css INCREASES

90
Q

What is the effect of an increased dosing rate of the Css?

A

Css INCREASES

91
Q

What is a maintenance dose?

A

The dose needed to maintain the Css (Steady State Concentration)

92
Q

What value do you need to calculate first to determine the maintenance dose?

A

Dosing rate at steady state

Dosing Ratess= CL x TC

93
Q

What is the equation for maintenance dose?

A

Dosing rate x dosing interval

94
Q

What is a loading dose?

A

An initial dose that can be given to reach target concentrations (TC) rapidly

= V x TC/F

95
Q

What are the advantages of a loading dose?

A

Useful when it would take a long to reach steady state, but you need to rapidly reach the TC
- E.g. in a drug with a long half-life

96
Q

What are the disadvantages of a loading dose?

A
  • Abrupt high concentration may be v.toxic

- Calculation takes into final volume of distribution, but inital dose is restricted to the blood

Pharmacology (64 decks)

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