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Intro to Pharmacology > Absorption and Distribution > Flashcards

Absorption and Distribution Flashcards

1
Q

What is pharmacokinetics?

3

A

intended to get the drug to the site of action so it may exert its effect (i.e., pharmacodynamics) and then remove the drug from the body

How the body affects the drug
Movement of drug through the body
Intended to get the drug to the site of action so it may exert its effect

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2
Q

What are the stages of PK?

A 
Liberation
Absorption
Distribution
Metabolism
Excretion
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3
Q

What is liberation?

A

the release of the drug from its dosage (administered) form

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4
Q

What is absorption?

A

the movement of drug from the site of administration to the blood circulation

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5
Q

What is distribution?

A

the process by which drug diffuses or is transferred from intravascular space to extravascular space (body tissues)

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6
Q

What is metabolism?

A

the chemical conversion of drugs into compounds which are easier to eliminate

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7
Q

What is excretion and through what pathways (3)?

A

the elimination of unchanged drug or metabolite from the body

via renal, biliary, or pulmonary processes

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8
Q

Where does absorption mainly occur?

3

A

GI tract
Skin
Lungs

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9
Q

Where does distribution and metabolism mainly occur?

4

A

Blood
Lymph
(liver and kidney)

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10
Q

How does elimination mainly occur?

3

A

Feces
Urine
Expired air

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11
Q

What are the various types of liberation?

3

A

Immediate
delyaed
Extended

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12
Q

Describe immediate release drugs

A

the medicine is formulated to release the medicinal drug without delay

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13
Q

Describe delayed release drugs

A

the medicine is formulated to release medicinal drug sometime after it is taken

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14
Q

Describe extended release drugs

A

the medicine is formulated to make the drug available over an extended period

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15
Q

Why does extended release have an advantage over the other types?
2

A

allowing a reduction in dosing frequency compared with immediate or delayed-release medicines. So you only have to take it once a day instead of multiple.
Lasts longer

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16
Q

Describe the enteral route

-how can it be administered?

A

Drug is placed directly into the gastrointestinal (GI) tract

-orally or via gastric feeding tube

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17
Q

Advantages of enteral (orally) route of administration?

5

A 
Simple
Inexpensive
Convenient
Painless
No infection risk
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18
Q

Disadvantages of enteral (orally) route?

6

A
  1. Drug exposed to harsh GI environment
  2. First pass metabolism
  3. Requires GI absorption
  4. Slow delivery to site of pharmacologic action
  5. Gastric mucosa irritation
  6. Unpleasant taste
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19
Q

Describe the enteral (rectal) route?

A

Drug is placed directly into the GI tract

Rectally

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20
Q

Advantages of the enteral (rectal) route?

6

A
  1. First pass metabolism partially avoided (if low)
  2. Unconscious patients and children
  3. Use in nauseous or vomiting patients
  4. Use in patients with poor GI absorption
  5. Easy to stop exposure
  6. Good for drugs affecting bowel (i.e. laxatives)
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21
Q

Disadvantages of the enteral (rectal) route?

3

A
  1. Variable absorption (not very reliable/you never know how much is actually absorbed)
  2. Invasion of privacy
  3. Irritating drugs contraindicated
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22
Q

What is the first pass effect (metabolism)?

A

Term used for the hepatic metabolism of a pharmacological agent when it is absorbed from the gut and delivered to the liver via the portal circulation.

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23
Q

What does a high first pass effect result in?

A

A smaller amount of the agent or drug reaching the systemic circulation when the agent is admistered orally

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24
Q

What is the extraction ratio?

A

Magnitude of the first pass hepatic effect

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25
Q

What is the equation for the extraction ratio

A

ER= CL liver/Q
CL liver = drug clearance through the liver
Q= hepatic blood flow

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26
Q

How do you determine systemic drug bioavailability (F)?

A

from the extent of absorption (f) and the extraction ratio (ER):
F = fraction absorbed (1 - ER)

Quantity of drug reaching systemic circulation / quantity of drug administered

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27
Q

What is the area under the curve represent?

A

Area Under the Curve (AUC) = total amount of drug reaching circulation

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28
Q

Parenteral VS Enteral?

A

IV goes straight to the body

Oral drugs go straight to the liver and are metabolized extensively before they go to the body

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29
Q

What are the types of parenteral routes of administration?

4

A

Intravascular (IV, IA)
Intrathecal (IT)
Intramuscular (IM)
Subcutaneous (SQ or SubQ)

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30
Q

What phase is bypassed in an IV route?

A

absorption phase

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31
Q

What is an IV routes bioavailability?

A

100%

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32
Q

Advantages of IV route?

3

A
  1. Precise and accurate dosing
  2. Almost immediate onset of action
  3. Large quantities may be given, fairly pain free
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33
Q

Disadvantages of IV routes?

5

A
  1. Greater risk of adverse effects
  2. High concentration attained rapidly
  3. Requires aseptic technique
  4. Risk of embolism
  5. OOPs factor
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34
Q

What is the intrathecal (IT) route?

A

placing a drug directly into the cerebrospinal fluid

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35
Q

Advantages of IT route?

A

bypasses the blood brain barrier

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36
Q

Disadvantages of the IT route?

3

A

Infection
Highly skilled personnel required
Aseptic technigue required

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37
Q

What is the IM intramuscular route of administration?

A

drug injected into skeletal muscle

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38
Q

Advantages of IM route?

2

A
  1. Very rapid absorption of drugs in aqueous solution

2. Repository and slow release preparations

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39
Q

Disadvantages of IM route?

3

A
  1. Pain at injection sites (for certain drugs)
  2. Increased risk of intramuscular hemorrhage
  3. Can affect lab tests (creatine kinase)
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40
Q

What is the subcutaneous (SQ or SubQ) route of administration?

A

Drugs injected into the tissue right below the skin

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41
Q

Advantages of the subcutaneous route?

A

Slow and constant absorption

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42
Q

Disadvantages of the Subcutaneous route?

A
  1. Absorption is limited by blood flow, affected if circulatory problems exist
  2. Concurrent administration of vasoconstrictor will slow absorption
  3. Small volumes (2-3 mL)
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43
Q

What are examples of the mucous membrane route?

6

A

inhalation, sublingual, nasal, vaginal, ocular, urinary

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44
Q

Advantages of the mucous membranes route?

4

A
  1. Avoids first-pass metabolism
  2. Direct delivery to affected tissue
  3. Rapid onset of action due to rapid access to circulation
    - Large surface area
    - High blood flow
  4. Simple, convenient, low infection risk
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45
Q

Disadvantages of Mucous membrane route?

A

Few drugs available to administer in this route

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46
Q

Describe the topical or transdermal route of administration

A

Highly lipophilic drugs can passively diffuse across the skin

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47
Q

Advantages of the transdermal route?

6

A
  1. 100% bioavailability
  2. Sustained, therapeutic plasma levels
    - Less peaks/valleys
  3. Avoids continuous infusion technique difficulties
  4. Low side effect incidence (smaller doses)
  5. Generally good patient compliance
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48
Q

Disadvanatges of the transdermal route?

4

A
  1. Skin irritation

2. Molecular weight

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49
Q

Which of the following routes would undergo the largest degree of first-pass metabolism?

A

Oral

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50
Q

What are the two definitions for absorption?

A

Process by which a drug enters the bloodstream without being chemically altered
OR
Movement of a drug from its site of application into the blood or lymphatic system

51
Q

Name the factors that affect drug absorption

6

A 
Administration route
Rate of dissolution of tablet(if oral)
Drug formulation
Physical factors
Diffusion
Transport
52
Q

What are the physical factors that affect drug absorption?

6

A 
Blood flow
Surface area
Contact time
GI motility
Gastric emptying time
Food
53
Q

What kind of circulation recieves 25% of cardiac output?

A

Sphlanic circulation

54
Q

How can GI motility affect drug absorption?

A

fasting or interdigestive state promote propulsion of food from the upper GI

55
Q

Describe how gastric emptying time can affect drug absorption

A

high fat meals, cold beverages, and anticholinergic drugs can delay gastric emptying time

56
Q

What does Fick’s law describe?

A

passive movement of molecules down its concentration gradient.

57
Q

What is the equation for Fick’s law?

A

Flux (J) (molecules per unit time) = (C1 - C2) · (Area ·Permeability coefficient) / Thickness

Diffusion Flux (F) = (C1-C2) x (Area x permeability)/ membrane thickness

58
Q

What do C1 and C2 respresent?

A

C1 is the higher concentration and C2 is the lower concentration

59
Q

What is the area in Ficks Law state?

A

Area across which diffusion occurs

60
Q

What is the permeability coefficient?

A

drug mobility in the diffusion path for lipid diffusion

61
Q

What does a partition coefficient reflect?

A

reflects how easily the drug enters the lipid phase from the aqueous medium.

62
Q

What does thickness mean in Fick’s Law?

A

Length of the diffusion path

63
Q

What is rate of transport across membranes dependent on?

6

A 
Molecular size
Lipophilicity
Charge
Degree of ionization
Blood flow
Protein binding
64
Q

What types of molecules passively diffuse the most rapidly?

4

A
  1. Small
  2. Hydrophobic/
    lipophilic
  3. Non-polar
  4. Non-ionized
65
Q

What is the pKa of a drug?

A

pKa = the pH at which 50% of the drug is ionized

66
Q

What are most drugs considered in regards to pH?

A

weak acids or weak bases

67
Q

How do weak bases interact with hydrogen?

A

accept hydrogen

68
Q

How to weak acids interact with hydrogen?

A

donate hydrogen

69
Q

Non-ionized or protonated molecules can do what more readily?

A

diffuse across the cell membrane easier because they are lipid soluable

70
Q

When the pH = pKa what is going on with the drug?

A

The drug is being absorbed and eliminated equally

71
Q

If the pH

A

-uncharged (non-ionized) form dominates

Weak acids exposed to low pH diffuse across cell membrane, but weak bases do not

72
Q

If the pH > pKa what is going on with the drug?

3

A

-charged (ionized) form dominates

Weak acids exposed to high pH (ionized) will not diffuse across cell membrane

73
Q

If a weak acid goes into the stomach what will happen?

A

The stomach is highly acidic. The drug molecule will remain unchanged and diffuse freely from GI into the blood stream

74
Q

What happens with the weak acid moved into the blood stream?

A

It was changed to an ioized form (charged form) and cannot diffuse back into the GI tract trapping it in the blood stream

75
Q

If the intestine environment is basic what kind of drug will remain unchanged?

A

weak bases (non-ionized)

76
Q

In the stomach (pH of 1), will aspirin (pKa = 3.5) have low or high absorption?

A

High

77
Q

What is the extent of ionization of drug molecules is influenced by?

A

pKa of the drug and the pH of the surrounding fluid

78
Q

When do drug molecules tend to be ionized?

A

when in a pH-opposite fluid (basic drugs are ionized and retained in acidic fluid)

79
Q

How do non-ionized drug molecules move across biological membranes?

A

passive diffusion

80
Q

What are the three ways ionized molecules can pass the cell membrane?

A

active transport mechanisms, facilitated diffusions, or endo/exocytosis`

81
Q

What is distribution?

A

Movement of drug to and from the blood and various tissues of the body
-fat, muscle, and brain tissue

82
Q

What factors affect distribution?

6

A 
Blood flow to the tissue
Size of the organ
Solubility of the drug
Capillary permeability
Binding
Volume of distribution
83
Q

How will tissues with high blood flow recieve drugs?

examples?3

A

recieve a significant amount in a short period of time

viscera, brain, muscle

84
Q

Organs with low perfusion will recieve drugs how?
examples?
2

A

receive drugs more slowly

fat and bone

85
Q

How does size affect organ distribution?

A

Very large organs (e.g., skeletal muscle) can take up large quantities of drug if allowed to reach steady state

86
Q

How would you treat an aspirin overdose?

A
  1. Alkalanize the urine (IV sodium bicarbonate)
  2. Increasing urine pH to just 6.3 doubles extent of ionization in urine, thereby trapping more of the drug there > elimination
87
Q

If you overdose on aspirin where does the majority go and why?

A

moves to the blood because its more acidic there

88
Q

What is the blood brain barrier made of and what can enter it?

A
  1. Astrocytic sheath
  2. Endothelium cells are more tightly joined
    - Slow the diffusion of water-soluble drugs
  3. Most non-ionized, lipid-soluble drugs readily enter the brain
89
Q

What does it mean when a drug has a low plasma protein binding affinity?

A
  1. Effectively restricted to the vasculature
  2. Only unbound drug is able to diffuse across membranes
  3. Low volume of distribution
  4. Potential of drug-drug interactions due to competing for binding sites
    Ex. warfarin
90
Q

What is the volume of drug (Vd) distribution?

A

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

91
Q

Bioavailabilty in laymens terms?

A

If i gave a certain amount of drugby mouth, how much of that drug ends upgetting into the systemic circulation

92
Q

Distribution is was?

A

The dispersion of a drug throughout your body

Where is it starting and where is it going?
Ex. from your vascular space to your extravascular space

93
Q

Equation for volume of distribution?

A

total mass absorbed/ concentration of drug in the plasma

94
Q

If you give not that much drug (10mg) but the plasma concentration is really high then what is your Vd?

A

low volume of distribution

95
Q

If the drug give the same 10mg of a different drug but the plasma concentration is really low then what does that mean about your Vd?

A

High volume of distribution

96
Q

What compartments can drugs distribute in?

3

A

plasma
interstitial fluid
intracellular fluid

97
Q

Vd is a proportionality constant defined as?

A

Amount of drug in the body/plasma concentration

98
Q

If drug likes to stay in the plasma we say it has a what kind of distribution?

A

low Vd

99
Q

If a drug likes to stay in the extravascular compartments we say it has what kind of distribution?

A

high Vd

100
Q

What factors affect the volume of distribution?

3 drug related factors and 4 patient related factors

A
  1. Drug pKa
  2. Extent of drug-plasma protein binding
  3. Partition coefficient of the drug in fat (lipid solubility)
  4. Vd may be affected by:
    - patient’s gender
    - patient’s age
    - patient’s disease
    - patient’s body composition (muscle mass, body fat, etc)
101
Q

If a drug as a high volume of distribution then what kind of dose do we need to give to reach our desired plasma concentration?

A

a high dose

102
Q

If a drug as a low volume of distribution then what kind of dose do we need to give to reach our desired plasma concentration?

A

a low dose

103
Q

What is the four compartment model of drug distribution?

A
  1. Blood- initally high but falls rapidly
  2. VRG- first to accumulate drug but its tissue uptake is variable
  3. Muscle- less perfused than vessel rich group but is a larger compartment
  4. Fat- much of the drug has already been metabolized and excreted by the time it gets to the fat but its the best holder of drug
104
Q

What is the order of capacity to accumulate drug for each compartment?

A
  1. Fat, 2. Muscle, 3. VRG, …. Bone, ligament and cartilage.
105
Q

If fat has the highest capacity to accumulate a drug, why is it’s peak lower than that of muscle for a single dose?

A

Because the body is already eliminating the drug and it takes time for the drug to accumulate into fat.

106
Q

Examples of drugs with high Vd for a 70 mg person?

A 
Amiodarone = 4620 L (66 L/kg)
Amitryptiline = 1050 L (15 L/kg)
Azithromycin = 2170 L (31 L/kg)
107
Q

What do we need to keep in mind about apparent volume of distribution?

A

Not a physical volume but an extrapolated volume based on the concentration of drug in plasma.

108
Q

A drug with a high Vd or that os taken up in large quantities by body tissue will be how present in the circulation?

A

largely removed from the circulation

109
Q

Explain saturation of tissue levels and how that affects the efficacy of the drug?

A

Tissues must be saturated before plasma levels can increase sufficiently to affect the target organ. (there is no more places in the tissue for the drug to go so it has to stay in the plasma)

110
Q

What kind of drugs would require a loading dose?

A

For drugs of equal potency, a drug with a high Vd typically requires a higher initial dose to establish therapeutic plasma levels (“loading dose”)

111
Q

So does the Vd (L/kg) give us a good estimate of?

A

how well the drug is distributed

112
Q

Vd values less than or equal to 0.071 L/kg indicate what about the drug?

A

That it is mainly in the circulatory system

113
Q

Vd values greater than or equal to 0.071 L/kg indicate what about the drug?

A

That the drug has gotten into specific tissue

114
Q

How are drug distribution and drug elimination related?

2

A
  1. Distribution is typically quicker than elimination

2. Drug distribution is affected by elimination

115
Q

Dosing decisions should be based on what?

2

A

Route

Desired tissue

116
Q 
The following factors affect drug distribution except:
Blood flow to the tissue
Solubility of the drug
Capillary permeability
Binding
Volume of distribution
All the above
A

All of the above

117
Q 
If all of these were low how what kind of distribution would you have?
Blood flow to the tissue
Solubility of the drug
Capillary permeability
Binding
Volume of distribution
A 
low Blood flow to the tissue= low Vd
Solubility of the drug= low Vd
Capillary permeability= low Vd
Binding affinity= Low Vd
Volume of distribution= Low Vd
118
Q

If a drug is really big/molecular weight is high then what kind of volume of distribution will it have?

A

low Vd

119
Q

If a drug likes to bind to plasma proteins it has what kind of Vd?

A

low

120
Q

If a drug likes to bind to extracellualr proteins it has what kind of Vd?

A

high

121
Q

If the drug is lipophilic it will have what kind of Vd?

A

high Vd

122
Q

If the drug is hydrophilic (really charged/ionized) it will have what kind of Vd?

A

low Vd

123
Q

If there is low albumin what will be the Vd?

A

low Vd?

Intro to Pharmacology (6 decks)

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