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Pharmacology - Fall > Lecture 2 and 3 - Pharmacokinetics > Flashcards

Lecture 2 and 3 - Pharmacokinetics Flashcards

1
Q

What is pharmacokinetics?

A

The study of how the body absorbs, distributes, metabolizes, and eliminates a drug over time

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2
Q

What is the primary site of absorption?

A

Small intestine

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3
Q

What is the primary site of excretion?

A

Kidneys

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4
Q

What is the primary site of metabolism?

A

Liver

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5
Q

What is the primary site of distribution?

A

Bloodstream

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6
Q

What is the clinical goal of pharmacokinetics?

A

Enhancing efficacy and decreasing toxicity

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7
Q

What is a better name for metabolism?

A

Biotransformation

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8
Q

What are the fastest routes of administration?

A

IV, inhalation, and sublingual

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9
Q

What are the slower routes of administration?

A

Transdermal and subcutaneous

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10
Q

What do drugs need to cross to move through the body?

A

Cell membranes

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11
Q

How do drugs cross cell membranes and which is the most common method?

A
  • Pass through channels or pores
  • Pass through the membrane with the aid of a transport system
  • Penetrate directly (most common)
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12
Q

Where are transporters found and what do they do?

A
  • Liver, kidneys, intestines, brain capillaries

- Transport a variety of drugs across membranes

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13
Q

Why do most drugs penetrate membranes directly?

A
  • Most drugs are too large to pass through channels

- Most drugs lack transport system to help them cross cell membranes

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14
Q

A drug must be ____ to penetrate cell membranes directly

A

Lipid soluble

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15
Q

What is the one-compartment model of drug disposition?

A

The drug does not extensively distribute into extravascular tissues

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16
Q

What is the two-compartment model of drug disposition?

A

The drug is administered to the central portion of the body, and then moves to the periphery

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17
Q

What is an example of a drug that demonstrates the one-compartment model?

A

Aminoglycosides

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18
Q

What is an example of a drug that demonstrates the multi-compartment model?

A

Benzodiazepines

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19
Q

What is bioavailability?

A

The fraction of unchanged drug reaching the systemic circulation following administration by any route

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20
Q

How are drug accumulation and dose lost related?

A

They are inversely proportional

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21
Q

What is volume of distribution?

A

The measure of the apparent space in the body available to contain the drug

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22
Q

What is clearance?

A

The measure of the ability of the body to eliminate the drug

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23
Q

What is a half-life?

A

The time required to change the amount of drug in the body by one-half during elimination

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24
Q

How do you calculate bioavailability?

A

(AUC admin route/AUC iv) * 100

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25
Q

How do you calculate drug accumulation?

A

1/ dose lost

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26
Q

How do you calculate volume of distribution?

A

Amount of drug in body (mg) / concentration of drug in plasma (mg/L)

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27
Q

How do you calculate clearance?

A

(0.693/t 1/2) * Vd

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28
Q

How you calculate half-life?

A

(0.693 * Vd) / Cl

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29
Q

What are 3 values that determine drug absorption?

A

1) Time to peak concentration (rate)
2) Peak concentration (rate and extent)
3) Area under the plasma concentration vs. time curve

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30
Q

What does the area under the plasma concentration (AUC) determine?

A
  • The extent of absorption of the drug

- The actual body exposure to the drug

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31
Q

Which route of administration have 100% bioavailability?

A

IV

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32
Q

What are 3 limitations for drug absorption?

A

1) Tissue perfusion
2) Diffusion-limited absorption
3) First pass effect

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33
Q

What is first pass effect?

A

Rapid liver inactivation of oral drugs

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34
Q

What is the advantage to enterohepatic cycling?

A
  • Reduces elimination

- Prolongs t 1/2

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35
Q

What are some factors that influence drug absorption?

A
  • Formulation
  • Water and lipid solubility
  • GI motility
  • Posture
  • Other drugs/foods
  • pKa
  • Gastric pH
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36
Q

When will an acidic drug be ionized and non-ionized?

A

Ionized in alkaline media and non-ionized in acid media

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37
Q

What can the Henderson-Hasselbalch equation be used for determining?

A

How much drug on each side of membrane

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38
Q

What is steady state?

A

When the rate of drug elimination equals the rate of administration

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39
Q

Which route of administration can attain steady state?

A

IV infusion

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40
Q

Which protein is the most common for bound drugs?

A

Albumin

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41
Q

Can bound or unbound drugs leave vessels?

A

Unbound b/c bound drugs are too big

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42
Q

What can be altered when a high quantity of a drug is bound?

A

Distribution time

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43
Q

What factors affect volume of distribution?

A

Solubility, charge, size

44
Q

What is volume of distribution important for?

A
  • Determining clearance of a drug from the body

- Determining loading dose of a drug

45
Q

What does a high Vd mean?

A

That the drug is not staying in the vascular compartment (it is extensively distributed)

46
Q

Can Vd surpass body fluid volume?

A

Yes

47
Q

How do you calculate loading dose?

A

Vd * desired plasma concentration

48
Q

How do you calculate dosing rate?

A
  • Clearance * target plasma concentration

- Amount / time

49
Q

How do you calculate maintenance dose?

A

(dosing rate / F) * dosing interval

50
Q

What are some factors that influence drug distribution in the body?

A
  • pKa of compound and pH of tissue compartment
  • Drug binding
  • Specialized distribution barriers (BBB, placenta)
51
Q

Where are acidic drugs more likely to be concentrated?

A

In blood compartment

52
Q

Where are basic drugs more likely to be concentrated?

A

Tissue

53
Q

Drug metabolites are usually more _____ than their parent compound

A

Polar

54
Q

What can happen with the ingestion of 2 or more drugs?

A

It can affect the rate of metabolism in one or both drugs

55
Q

What are phase 1 reactions?

A

Oxidation, reduction, and hydrolysis reactions

56
Q

What are phase 2 reactions?

A

Glucuronidation, sulfation, and acetylation reactions

57
Q

When do phase 1 reactions take place?

A

Between absorption and metabolism

58
Q

When do phase 2 reactions take place?

A

Metabolism and elimination

59
Q

Most drugs are ____ order

A

First

60
Q

What is first order metabolism?

A

When the rate of drug metabolism is proportional to dose

61
Q

What is zero order metabolism?

A

When the rate of drug metabolism remains constant over time

62
Q

What is the importance of clearance?

A

Provides an index of the efficiency by which a drug is removed from the body

63
Q

What factors can cause clearance to change?

A
  • Disease state

- Genetic and environmental factors

64
Q

What is clearance needed for determining?

A

Dosing rate and maintenance dose

65
Q

How many half-lives are required to eliminate a single dose of a drug from the body?

A

Around 5

66
Q

Do high or low MW drugs enter the kidney?

A

Low

67
Q

What does the kidney filter back into the blood and what does it keep in the urine?

A
  • Filters lipid soluble drugs into the blood

- Keeps non-lipid soluble, polar, and ionized drugs in the urine

68
Q

What are the 3 steps of renal elimination?

A

1) Glomerular filtration
2) Tubular reabsorption
3) Tubular secretion

69
Q

What is used to assess renal impairment?

A

Creatinine clearance

70
Q

What are some examples of drug transporters?

A

1) Organic anion transport proteins
2) Organic cation transport proteins
3) P-glycoprotein
4) Multidrug resistance-associated proteins (MRP)

71
Q

Bile excretion favours compounds with _____ MW

A

Higher

72
Q

What is a prodrug?

A

The inactive form of a drug

73
Q

How does a prodrug become active?

A

Through metabolism

74
Q

Does a prodrug increase or decrease bioavailability and why?

A

Increases because it prevents the drug from undergoing first pass metabolism

75
Q

What happens if a drug becomes associated with fat?

A

It alters distribution and elimination

76
Q

Which group of enzymes metabolizes drugs in the liver?

A

Microsomal enzyme system, or P450 system

77
Q

How many families make up the P450 system?

A

12

78
Q

What do the 12 families of the P450 system do?

A
  • 3 families metabolize drugs (CYP 1, 2, 3)

- 9 families metabolize steroids and fatty acids

79
Q

What are the 2 most prevalent CYP enzymes?

A

CYP 3A4 and 3A5

80
Q

What does CYP 2D6 do?

A

Metabolizes morphine and codeine

81
Q

What are 3 main substrates of CYP 3A4?

A

Acetaminophen, cocaine, and testosterone

82
Q

What is one main inducer of CYP 3A4?

A

St. John’s wort

83
Q

What is one main inhibitor of CYP 3A4?

A

Grapefruit juice

84
Q

What is the importance of phenytoin with respect to CYP enzymes?

A

Over time phenytoin causes an increased expression level for CYP 3A4

85
Q

What does rifampicin do to CYP450 enzymes?

A

Induces them

86
Q

How do CYP enzymes get induced?

A

Drug binds to a site on the gene encoding the enzyme which turns on synthesis of more enzyme

87
Q

What does xenobiotic mean?

A

Any foreign substance you ingest

88
Q

Can the induction mechanism change in response to environment?

A

Yes

89
Q

What is the importance of induction with respect to pharmacokinetics?

A

Increased clearance and decreased half-life

90
Q

What is the important of induction with respect to pharmacodynamics?

A

Decreased response

91
Q

Are CYP enzymes only induced by drugs?

A

No, they can be induced by environment/lifestyle factors and herbal/nutritional supplements

92
Q

Smoking has an effect on ______ and ______ of drugs

A

Clearance and metabolism

93
Q

What is the importance of cimetidine with respect to CYP enzymes?

A

It is a potent inhibitor of several CYP enzymes

94
Q

What are 4 drug interactions with cimetidine?

A
  • Warfarin
  • Benzodiazepines
  • Phenytoin
  • Morphine
95
Q

What is the importance of inhibition with respect to pharmacokinetics?

A

Decreased clearance and increased half-life

96
Q

What is the important of inhibition with respect to pharmacodynamics?

A

Increased response and duration

97
Q

For an inhibitor, are effects immediate or delayed?

A

Immediate

98
Q

For an inducer, are effects immediate or delayed?

A

Delayed

99
Q

How can you reduce the risk of interactions?

A

Reduce the number of drugs

100
Q

What are the 3 polymorphisms of some CYP enzymes?

A
  • Poor metabolizer
  • Extensive metabolizer
  • Ultra-extensive metabolizer
101
Q

What does a poor metabolizer mean?

A

Increased toxicity

102
Q

What does an ultra-extensive metabolizer mean?

A

Reduced response

103
Q

What does an extensive metabolizer mean?

A

Normal response

104
Q

In which age groups in rate of drug disposition most likely impaired?

A

Very young and very old

105
Q

What needs to be modified in a patient who has a disease that impairs organ function?

A

Dosage

Pharmacology - Fall (15 decks)

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