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

Lecture 2 and 3 - Pharmacokinetics Flashcards

(105 cards)

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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
How do you calculate drug accumulation?
1/ dose lost
26
How do you calculate volume of distribution?
Amount of drug in body (mg) / concentration of drug in plasma (mg/L)
27
How do you calculate clearance?
(0.693/t 1/2) * Vd
28
How you calculate half-life?
(0.693 * Vd) / Cl
29
What are 3 values that determine drug absorption?
1) Time to peak concentration (rate) 2) Peak concentration (rate and extent) 3) Area under the plasma concentration vs. time curve
30
What does the area under the plasma concentration (AUC) determine?
- The extent of absorption of the drug | - The actual body exposure to the drug
31
Which route of administration have 100% bioavailability?
IV
32
What are 3 limitations for drug absorption?
1) Tissue perfusion 2) Diffusion-limited absorption 3) First pass effect
33
What is first pass effect?
Rapid liver inactivation of oral drugs
34
What is the advantage to enterohepatic cycling?
- Reduces elimination | - Prolongs t 1/2
35
What are some factors that influence drug absorption?
- Formulation - Water and lipid solubility - GI motility - Posture - Other drugs/foods - pKa - Gastric pH
36
When will an acidic drug be ionized and non-ionized?
Ionized in alkaline media and non-ionized in acid media
37
What can the Henderson-Hasselbalch equation be used for determining?
How much drug on each side of membrane
38
What is steady state?
When the rate of drug elimination equals the rate of administration
39
Which route of administration can attain steady state?
IV infusion
40
Which protein is the most common for bound drugs?
Albumin
41
Can bound or unbound drugs leave vessels?
Unbound b/c bound drugs are too big
42
What can be altered when a high quantity of a drug is bound?
Distribution time
43
What factors affect volume of distribution?
Solubility, charge, size
44
What is volume of distribution important for?
- Determining clearance of a drug from the body | - Determining loading dose of a drug
45
What does a high Vd mean?
That the drug is not staying in the vascular compartment (it is extensively distributed)
46
Can Vd surpass body fluid volume?
Yes
47
How do you calculate loading dose?
Vd * desired plasma concentration
48
How do you calculate dosing rate?
- Clearance * target plasma concentration | - Amount / time
49
How do you calculate maintenance dose?
(dosing rate / F) * dosing interval
50
What are some factors that influence drug distribution in the body?
- pKa of compound and pH of tissue compartment - Drug binding - Specialized distribution barriers (BBB, placenta)
51
Where are acidic drugs more likely to be concentrated?
In blood compartment
52
Where are basic drugs more likely to be concentrated?
Tissue
53
Drug metabolites are usually more _____ than their parent compound
Polar
54
What can happen with the ingestion of 2 or more drugs?
It can affect the rate of metabolism in one or both drugs
55
What are phase 1 reactions?
Oxidation, reduction, and hydrolysis reactions
56
What are phase 2 reactions?
Glucuronidation, sulfation, and acetylation reactions
57
When do phase 1 reactions take place?
Between absorption and metabolism
58
When do phase 2 reactions take place?
Metabolism and elimination
59
Most drugs are ____ order
First
60
What is first order metabolism?
When the rate of drug metabolism is proportional to dose
61
What is zero order metabolism?
When the rate of drug metabolism remains constant over time
62
What is the importance of clearance?
Provides an index of the efficiency by which a drug is removed from the body
63
What factors can cause clearance to change?
- Disease state | - Genetic and environmental factors
64
What is clearance needed for determining?
Dosing rate and maintenance dose
65
How many half-lives are required to eliminate a single dose of a drug from the body?
Around 5
66
Do high or low MW drugs enter the kidney?
Low
67
What does the kidney filter back into the blood and what does it keep in the urine?
- Filters lipid soluble drugs into the blood | - Keeps non-lipid soluble, polar, and ionized drugs in the urine
68
What are the 3 steps of renal elimination?
1) Glomerular filtration 2) Tubular reabsorption 3) Tubular secretion
69
What is used to assess renal impairment?
Creatinine clearance
70
What are some examples of drug transporters?
1) Organic anion transport proteins 2) Organic cation transport proteins 3) P-glycoprotein 4) Multidrug resistance-associated proteins (MRP)
71
Bile excretion favours compounds with _____ MW
Higher
72
What is a prodrug?
The inactive form of a drug
73
How does a prodrug become active?
Through metabolism
74
Does a prodrug increase or decrease bioavailability and why?
Increases because it prevents the drug from undergoing first pass metabolism
75
What happens if a drug becomes associated with fat?
It alters distribution and elimination
76
Which group of enzymes metabolizes drugs in the liver?
Microsomal enzyme system, or P450 system
77
How many families make up the P450 system?
12
78
What do the 12 families of the P450 system do?
- 3 families metabolize drugs (CYP 1, 2, 3) | - 9 families metabolize steroids and fatty acids
79
What are the 2 most prevalent CYP enzymes?
CYP 3A4 and 3A5
80
What does CYP 2D6 do?
Metabolizes morphine and codeine
81
What are 3 main substrates of CYP 3A4?
Acetaminophen, cocaine, and testosterone
82
What is one main inducer of CYP 3A4?
St. John's wort
83
What is one main inhibitor of CYP 3A4?
Grapefruit juice
84
What is the importance of phenytoin with respect to CYP enzymes?
Over time phenytoin causes an increased expression level for CYP 3A4
85
What does rifampicin do to CYP450 enzymes?
Induces them
86
How do CYP enzymes get induced?
Drug binds to a site on the gene encoding the enzyme which turns on synthesis of more enzyme
87
What does xenobiotic mean?
Any foreign substance you ingest
88
Can the induction mechanism change in response to environment?
Yes
89
What is the importance of induction with respect to pharmacokinetics?
Increased clearance and decreased half-life
90
What is the important of induction with respect to pharmacodynamics?
Decreased response
91
Are CYP enzymes only induced by drugs?
No, they can be induced by environment/lifestyle factors and herbal/nutritional supplements
92
Smoking has an effect on ______ and ______ of drugs
Clearance and metabolism
93
What is the importance of cimetidine with respect to CYP enzymes?
It is a potent inhibitor of several CYP enzymes
94
What are 4 drug interactions with cimetidine?
- Warfarin - Benzodiazepines - Phenytoin - Morphine
95
What is the importance of inhibition with respect to pharmacokinetics?
Decreased clearance and increased half-life
96
What is the important of inhibition with respect to pharmacodynamics?
Increased response and duration
97
For an inhibitor, are effects immediate or delayed?
Immediate
98
For an inducer, are effects immediate or delayed?
Delayed
99
How can you reduce the risk of interactions?
Reduce the number of drugs
100
What are the 3 polymorphisms of some CYP enzymes?
- Poor metabolizer - Extensive metabolizer - Ultra-extensive metabolizer
101
What does a poor metabolizer mean?
Increased toxicity
102
What does an ultra-extensive metabolizer mean?
Reduced response
103
What does an extensive metabolizer mean?
Normal response
104
In which age groups in rate of drug disposition most likely impaired?
Very young and very old
105
What needs to be modified in a patient who has a disease that impairs organ function?
Dosage

Pharmacology - Fall (15 decks)

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