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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
What is the pKa?
pH at which 50% if the drug is ionized, 50% is unionzed
26
If the pH is greater than pKa , what form will the drug be in?
pH > pKa= DEPROTONATED
27
If the pH is less than pKa, what form will the drug be in?
pH
28
Where is the body are weak acids and weak bases favored for absorption?
Stomach= low pH= protonated= weak acids more readily absorbed Intestine= high pH= unprotonated= weak bases more readily absorbed
29
What pH favors absorption of Salicylic acid, pKa = 3?
Less than 3 *****Protonated and unionized
30
What pH favor absorption of Amphetamine, pKa= 10?
Greater than 10 *****Unprotonated and unionized
31
How much salicylic acid, pKa=3, will be absorbed from the small intestine, which has a pH of 7?
N/A See ppt.
32
In the stomach (at pH=2), what is the ratio of unionized to ionized ASA?
N/A See ppt.
33
At a pH of 8, what is the ratio of unionized to ionized amphetamine (pKa=10)?
N/A See ppt.
34
What is the antilog of -4?
0.0001
35
What is the antilog of -3?
0.001
36
What is the antilog of -2?
0.01
37
What is the antilog of -1?
0.1
38
What is the antilog of 0?
1
39
What is the antilog of 1?
10
40
What is the antilog of 2?
100
41
What is the antilog of 3?
1,000
42
What is the antilog of 4?
10,000
43
What is distribution?
Process by which a drug leaves the circulation and enters the tissues perfused by the blood
44
What are the four general factors that affect drug distribution?
1) Cardiovascular factors 2) Tissue binding 3) Drug molecule size 4) Lipid solubility
45
What are the four cardiovascular factors that affect drug absorption?
1) CO 2) Regional blood flow 3) Capillary permeability 4) Binding to plasma proteins
46
What is drug metabolism?
Biotransformation--making a drug more soluble for elimination from the body
47
What is Phase I of biotransformation?
Generation of a more polar molecule by exposing a functional group
48
What is Phase II of biotransformation?
Conjugation of a drug to yield a more water soluble product to be excreted
49
What enzymes mediate Phase I biotransformation?
Cytochrome P450's or "CYPs"
50
What are the most common reactions of Phase II biotransformation?
Glucuronidation Sulfation Acetylation *****Know that these are conjugation processes that are making the drugs more polar and water soluble for excretion.*****
51
What are the key sites of biotransformation?
``` GI Lungs Skin Kidneys Brain ```
52
What is the "first-pass" effect?
Entrance into the portal circulation and initial metabolism of a drug by the liver
53
What is the primary mechanism of drug elimination? Secondary?
Primary= renal excretion Secondary= fecal via hepatic secretion into bile
54
What are the factors that alter renal excretion of a drug?
- GFR (glomerular filtration rate) - Binding to plasma proteins - Urine pH
55
What is the "Volume of Distribution (V)?"
Measure of the space in the body available for the drug *****Amount of drug in body/ Concentration of drug in blood or plasma*****
56
What is "Clearance (CL)?"
Measure of the ability of the body to eliminate a drug *****Rate of elimination/ concentration of drug*****
57
Generally, what does a large V mean?
Greater extent to which the drug distributes to the extravascular tissue
58
What does a V similar to the blood volume mean?
Majority of the drug is located in the vasculature
59
What does a V 100x the volume of the blood mean?
Majority of the drug is located in the extravascular tissue e.g. fat
60
What is zero-order elimination?
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
When is zero-order kinetics/ elimination observed?
When the body's capacity to eliminate the drug is saturated
62
Draw an example of zero-order elimination graphically.
N/A
63
What is first-order elimination?
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
Draw an example of first-order elimination graphically.
N/A
65
What is capacity-limited elimination?
A point at which the concentration of drug has saturated the elimination capacity of the system *****Zero-order process*****
66
What is flow-dependent elimination?
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
What is the consequence of continuous dosing with a drug that undergoes capacity-limited elimination?
Dangerous toxic levels of drug will accumulate
68
What drugs are associated with capacity-limited elimination?
Phenytonin ASA Alcohol
69
What drug is associated with flow limited elimination?
Propanolol
70
What is the half-life of a drug?
Time required for the plasma concentration of a drug to decrease by 50%
71
What is the half-life a drug dependent on?
- Volume of distribution (V) | - Clearance (CL)
72
After two half-lives, how much drug has been eliminated?
75%
73
How many half-lives does it take for a drug to be "fully eliminated?"
4-5 half-lives
74
What happens to the half-life of a drug if you reduce the clearance of the drug e.g. from renal insufficiency/failure?
Half-life INCREASES
75
How does increasing the Volume of Distribution (V) impact the half-life of the drug?
Increases the half-life
76
How is the initial plasma concentration calculated?
- 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
What is the impact of calculating the initial plasma concentration in a one compartment vs. a two compartment model?
- 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
What is an accumulation factor?
= 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
When does accumulation of a drug become detectable?
If the dosing interval is shorter than 4 half-lives
80
What is bioavailability? What is the equation for bioavailability?
The amount of drug that reaches the systemic circulation F= f x (1-ER) f= extent of absorption from gut
81
What is the bioavailability of a drug given IV? How does this compare to a drug given PO?
``` IV= 100% PO= much less ```
82
What is the extraction ratio (ER)?
Effect of first-pass metabolism on bioavaliability
83
What are the determinants of the extraction ratio?
ER= Hepatic Clearance/ Hepatic Blood Flow
84
What is the TC?
Target concentration
85
What is the MEC?
Minimum effective concentration
86
What is the Css?
"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
How long will it take to reach the Css?
4-5 half-lives
88
What is the therapeutic window?
Concentration range between the MEC for the desired effect and the MEC for the toxic effect
89
If the clearance of a drug decreases from renal insufficiency or failure, what happens to the Css?
Css INCREASES
90
What is the effect of an increased dosing rate of the Css?
Css INCREASES
91
What is a maintenance dose?
The dose needed to maintain the Css (Steady State Concentration)
92
What value do you need to calculate first to determine the maintenance dose?
Dosing rate at steady state Dosing Ratess= CL x TC
93
What is the equation for maintenance dose?
Dosing rate x dosing interval
94
What is a loading dose?
An initial dose that can be given to reach target concentrations (TC) rapidly = V x TC/F
95
What are the advantages of a loading dose?
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
What are the disadvantages of a loading dose?
- 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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