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Pharmocokinetics Flashcards

1
Q

What does bioavailability mean?

A

Amount of drug that ends up being available to cause an effect

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2
Q

What is the first pass effect?

A

Drug is metabolized by the liver before it hits the vascular system

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3
Q

What does solubility mean?

A

Ability of a drug to be dissolved in one state or the other

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4
Q

What is the oil/water partition coefficient?

A

Reflects lipophilic nature of the drug vs. Hydrophilic nature of the drug

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5
Q

What is the blood/gas partition coefficient?

A

How much or little does the drug like to be dissolved in gas

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6
Q

What is the blood/tissue partition coefficient?

A

How much or little does the drug like to be dissolved in tissue

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7
Q

What is pKa?

A

A scientifically determined pH at which 50% of an acid or base exists in an uncharged (unprotenated) form and 50% is charged (protenated).

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8
Q

Are acidic compounds charged when they are protenated or unprotenated?

A

Unprotenated

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9
Q

Are acidic compounds uncharged in the protenated or unprotenated form?

A

Protenated

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10
Q

Are basic compounds charge in the protenated or unprotenated form?

A

Protenated

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11
Q

Are basic compounds uncharged in the protenated or unprotenated form?

A

Unprotenated

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12
Q

What form ionized or unionized can cross the phospholipid cell membrane?

A

Unionized (unprotenated)

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13
Q

At what pKa the onset of drugs the fastest?

A

The closer the pKa is to physiologic pH

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14
Q

How does a small change in pH affect the pKa equation?

A

It can greatly affect it - can even cause ion trapping

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15
Q

What is ion trapping?

A

When drugs can become trapped in a compartment with low or high pH

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16
Q

What is the definition of absorption?

A

Movement of drug molecules across membranes and thus into blood

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17
Q

What route avoids absorption?

A

IV

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18
Q

What is Fick’s law?

A

The rate of diffusion is proportional to [(the concentration gradient) x (the surface area for absorption) x (drug solubility of the drug in that membrane)] divided by [(the membrane thickness (or distance it needs to go to diffuse)) x (the size of the molecule)]

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19
Q

What are the routes for solute so to cross physiologic membranes?

A
  • diffusion through lipid
  • Diffusion through aqueous channels
  • Carrier
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20
Q

What mechanism do gases use to get across a lipophilic membrane?

A

Diffusion - quite readily

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21
Q

What mechanism does hydrophobic molecules use to get across the lipophilic membrane?

A

Diffusion

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22
Q

What mechanism do small polar molecules use to get across the lipophilic membrane?

A

Diffusion

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23
Q

What mechanism do large polar molecules use to get across the lipophilic membrane?

A

Need carrier

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24
Q

What mechanism do charge molecules used to get across the lipophilic membrane?

A

Need pores or amino acids that are transported into the cell

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25
What are 2 main components taken into consideration when looking at the ease of crossing the lipophilic membrane?
Molecular size | Molecular affinity
26
What is meant by volume of distribution?
A parameter used to estimate the distribution of drug in the body - not all drugs distribute evenly.
27
What 3 factors must be present for volume of distribution to have any validity?
1. The drug must be instantaneously distributed and no metabolism should have occurred 2. No portion of the drug should have been excreted 3. No portion of the drug should have been sequestered
28
What are compartment models used for?
To predict elimination
29
What is a one compartment model?
The assumption is that the drug is distributed instantly and simultaneously in an even manner throughout the entire body.
30
What is a two compartment model?
Immediately after administration, the drug is distributed through high flow tissues and their after, there is an equilibrium formed where there is a linear line.
31
Water are considered high flow tissues?
Blood, brain, heart, liver, lungs
32
What is a multi-compartmental model?
Drug is administered and delivered into central compartment (vasculature). It is then redistributed to highly perfused organs and then comes into equilibrium with the central compartment. There is also a phase where it is distributed to the vessel poor compartment. All this then becomes in equilibrium with elimination phase
33
What is considered vessel poor compartments?
Muscle, bone, teeth, tendons, and fat
34
What is phase 1 metabolism?
Oxidation-reeducation reaction in hepatocytes By mixed function oxidase enzymes found on the smooth ER of the hepatocytes - makes compounds more polar (allows them to be more easily eliminated by kidney or secreted into the bile).
35
What is phase 2 metabolism?
Polar molecule attaches to another larger molecule for increased water solubility
36
Where does phase 2 metabolism occur?
Hepatocytes by enzymes located in the cytoplasm and in the smooth ER
37
What is the most common type of phase 2 metabolism?
Glucuronic acid conjugation - most important step in inactivation of the drug and elimination of the apparent drug effect
38
What does the rough ER do?
Transports material through the cell and produces proteins in sacks which are then sent to the Golgi body or inserted into the cell membrane
39
What does the smooth ER do?
Makes up proteins and lipids that get exported by the cell | Controls calcium levels in the nucleus and detoxifies poisons, alcohol, and drugs
40
What is first pass metabolism?
100% of dose is ingested orally. In the stomach and gut, 70% is ingested and transported into the vasculature. Inside the liver, as the drug transverses the portal system, a fair amount is eliminated by phase 1 and 2 elimination. Only about 15% of the dose enters the blood and is delivered through the heart and lungs to the target organ.
41
Where does esterase metabolism take place?
Neuromuscular junction or within the plasma
42
In esterase metabolism, what enzyme binds acetylcholine CoA and Choline?
Choline acetylcholine transferase
43
When acetyl CoA and Choline are blinded together, what forms and what is recycled?
Acetylcholine is formed and CoA is recycled
44
Describe the process of how acetylcholine is released into the cell membrane and then broken down.
Acetylcholine is stored in small vesicles of the neuromuscular end plate. With the arrival of an impulse, acetylcholine is released form vesicles into the synaptic cleft. Once in the synaptic cleft in sufficient concentration, it causes a depolarization of the receptor membrane. In the synaptic cleft, acetylcholine esterase is used to break down acetylcholine into acetate and choline.
45
What happens to the acetate and choline that are broken down?
They are recycled back into acetyl CoA and choline and the process starts over.
46
Describe the process of esterase metabolism.
Acetyl CoA + Choline (choline acetyl transferase joins the two together) forms acetylcholine (CoA is recycled). Acetylcholine is released into cleft. Acetylcholine esterase then breaks down the acetylcholine into acetate and choline which is recycled back and the cycle begins all over again.
47
How is succinylcholine broken down?
It diffuses away from the neuromuscular junction and is broken down by plasma esterase a into succinctness and choline. It is not broken down in the synaptic cleft - has a prolonged effect on acetylcholine receptors.
48
What is the primary route of elimination in the body?
Kidneys
49
Do drugs that are highly protein bound have longer or shorter elimination half lives? Why?
Longer because of acceptor sites on albumin - acts as a resin ore of active drug
50
Do filtration pores have a negative or positive charge?
Slightly negative - this is why it's best to have a non-polar molecule delivered to the kidney
51
Where are drugs excreted in the kidney?
Proximal tubule
52
Which types of drugs are excreted most readily through the kidneys?
Water soluble
53
What do lipid soluble drugs need before being eliminated?
Liver metabolism - phase 1 or phase 2 - to make the more water soluble.
54
Are weak acids excreted more readily in alkaline or acidic urine?
Alkaline
55
Are weak bases excreted more readily in alkaline or acidic urine?
Acidic
56
Is the alpha elimination curve a more rapid or slower decline in drug concentration?
Rapid
57
Is the beta elimination cure a more rapid or slower decline in drug concentration?
Slower
58
What is first order kinetics?
If you administer a drug, the rate of decline in its concentration will be exponential. Ex. A constant fraction of drug is eliminated per unit time - most popular
59
What is zero order kinetics?
If you administer a drug, the rate of decline in its concentration will be linear Ex. A constant amount of drug is eliminated per unit time
60
When does zero order kinetics occur?
When there is saturation of some rate limiting step in the elimination process. This may occur when the amount of drug is too great to be handled by a particular metabolic enzyme, secretory process, transport protein, or cofactors.
61
What is elimination half-life?
The time for plasma concentration to drop by 1/2 It is a constant
62
What is the Michaels-mention theory?
That drugs are metabolized by zero order kinetics at high levels and first order kinetics at lower levels
63
What is context-sensitive elimination?
Accounts for steady state administration over time Ex. Propofol infusion - longer proposal drip is on, the longer it takes the patient to recover from it.
64
What accounts for majority of the protein binding?
Albumin
65
What binds acidic drugs?
Plasma albumin
66
What binds basic drugs?
Beta globulin and alpha 1 glycoprotein
67
Is protein binding saturable?
Yes. Can lead to a non linear response to the protein bound drug.
68
What does protein binding do to drug metabolism?
Delays it
69
What other factors play into the kinetics of drug metabolism?
- age - Gender - Temp - co-morbidities - Pharmacogenetics and Pharmacogenetics
70
What is the definition of pharmacokinetics?
What the body does to the drug once it is introduce into the system.

Anesthesia Pharm (5 decks)

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