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Pharmacokinetics & Pharmacodynamics Flashcards

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1
Q

What are pharmacokinetics?

A

The effects the body has on the drug

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2
Q

What are pharmacodynamics?

A

The effects the drug has on the body

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3
Q

What is the path an oral drug takes to get to the blood stream?

A

Mouth, stomach, intestines, portal vein, liver, blood

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4
Q

Drugs can diffuse to which organs relevant to ADME once they reach the blood?

A

Liver, Kidneys, Tissues, Site of Action

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5
Q

What characteristics are required for passive diffusion across a membrane?

A

Uncharged, unbound and non-polar

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6
Q

What does Lipinski’s Rule describe the characteristics of?

A

Drugs that are orally bioavailable

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7
Q

What are Lipinski’s Rules of 5?

A

Drugs should have less than 5 hydrogen bond donors, less than 10 hydrogen bond acceptors, a LogP less than 5 and a MW under 500 Da

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8
Q

What is LogP?

A

The logarithm of the ratio of the concentration of drug solvated by n-octanol and the concentraiton of drug solvated by water

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9
Q

What are the two main tenets of the free drug hypothesis?

A

Within the blood, drugs exist in equilibrium between being protein-bound and free and only free drugs can permeate to the site of action and have therapeutic efficacy

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10
Q

Because of protein binding in the plasma, what can be said about the relationship between plasma drug concentrations and concentrations at the site of action?

A

These concentrations aren’t always equivalent

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11
Q

How does protein binding influence drug elimination?

A

Because bound drug can’t be filtered by the kidneys, the circulation time (half-life) of the drug increases

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12
Q

What are some additional considerations for drugs with high protein binding?

A

Pathophysiological changes to organs responsible for distribution and elimination might change drug half-life

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13
Q

How does pH influence absorption?

A

At a pH far from a drug’s pI, the majority of the drug will be ionized and unable to permeate through a membrane which will decrease absorption

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14
Q

Generally, is the gut more acidic or basic?

A

Basic

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15
Q

How can charged and polar drugs cross membranes?

A

Active transport/using membrane transporters

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16
Q

What is AUC (conceptually)?

A

The total exposure to a drug after dosing

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17
Q

How is AUC measured?

A

It is the sum of the area under the curve of a time vs drug concentration curve

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18
Q

What is bioavailability?

A

The percentage of drug that reaches the blood after an extravascular dose

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19
Q

How can bioavailability be measured?

A

Find the ratio between the AUC after an extravascular dose and an intravascular dose

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20
Q

What is considered an extravascular dose?

A

Any dose that isn’t IV (IM, SC, oral, direct target)

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21
Q

What factors can influence absorption?

A

pH, solubility, MW

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22
Q

What factors can influence bioavailability?

A

first-pass metabolism, intestinal wall permeability and low exposure to absorptive surfaces

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23
Q

At what bioavailability should you switch from oral dosing?

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A

Around 10-20% bioavailability

24
Q

What is volume of distribution?

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A

The apparent volume that a drug distributes into

25
If a drug's Vd is the central compartment, what is that referring to?
Systemic circulation/blood
26
What's the largest factor influencing a person's Vd?
Their size
27
How can protein binding influence Vd?
Since protein binding decreases the measurable concentration of drug in plasma, the apparent Vd decreases are protein binding increases
28
What does Ke represent?
The elimination rate constant
29
What is Ke conceptually?
The fraction of drug eliminated over unit of time
30
What order of elimination do most drugs fall under and how does elimination rate change with respect to the dose of drug under this order of elimination?
First-order; elimination rate increases proportionally with dose
31
What order of elimination is associated with a saturated elimination rate?
Zero-order
32
How does elimination rate change with respect to the dose of a drug under zero-order elimination
It doesn't change
33
What is half-life?
The time is take a drug to decrease in concentration by 50%
34
How can you convert between half-life and elimination rate constant?
Half-life = .7/ke
35
How can you estimate ke/half-life/Vd after dosing someone?
Measure the concentration of drug at two timepoints, determine the natural log of both concentrations and plot them on a graph of ln(conc.) against time. From the slope of this curve, you can determine the elimination rate constant. From the ke, you can determine the half-life. Extrapolate the curve to time = 0 and determine the initial concentration by reversing the natural log of the y-intercept. With this value, Vd/F (if administered non-IV) = initial dose/initial concentration
36
What is clearance?
The rate a volume is cleared of drug
37
What are the three main types of clearance?
Renal, hepatic and respiratory
38
What is the primary mechanism of clearance?
Hepatic
39
What is the difference between elimination rate and elimination rate constant?
Elimination Rate depicts a mass of drug elimination per unit of time while elimination rate constant depicts a fraction of the total drug eliminated per unit of time
40
What is the steady state concentration of a drug?
The concentration of a drug where administration and absorption equal elimination
41
Continuously infusing a drug at the rate of elimination will bring the drug concentration to what?
Steady state
42
What is an IV bolus? Why are these dose forms used?
An high concentration infusion of a drug to produce an immediate effect. These are used when the therapeutic effect of a drug is needed immediately
43
What are some examples of situations that would elicit IV bolus dosing?
Preventing overdose, anaphylaxis, cardiac arrest or providing immediate pain relief or rescuing from severe dehydration
44
How does intermittent dosing differ from continuous infusion?
Intermittent dosing occurs at consistent intervals while continuous infusion administers the drug at a slower rate constantly to maintain steady state
45
What situations would necessitate continuous infusion over intermittent dosing?
Dosing drugs with small therapeutic windows (chemotherapeutics) or treating severe infections
46
After how many half-lives is steady state reached?
4-5
47
What happens when dosing intervals increase but the daily dose remains fixed?
The peak:trough ratio increases but the drug levels continue to fluctuate around the same steady state
48
What is one benefit of oral intermittent dosing over other mechanisms?
The peaks and trough are narrower
49
How can pathophysiology change dosing intervals?
If the pathophysiology impacts clearance, then the dosing interval needs to be changed to compensate for the change in half-life
50
When modeling PKPD, how can receptor occupancy be measured?
The slope of a sigmoidal effect against time curve informs on occupancy
51
What metric can be calculated to measure receptor occupancy from a PD curve?
The hill coefficient
52
What do PK curves plot and what can these curves inform you of?
Concentration of drug against time; they can inform you of rate of absorption, distribution, elimination (plus related PK parameters like Vd, clearance, half-life)
53
What do PD curves plot and what can these curves inform you of?
Degree of effect against concentration of drug; they can inform you of maximum drug efficacy (Emax) and metrics of drug potency (EC/IC50), ED50, toxicity (LD50) and therapeutic index (LD50:ED50)
54
What is the hysteresis loop phenomenon?
A phenomenon that occurs when the concentration of a drug doesn't correlate with the degree of effect because of a distribution delay or disequilibrium between the drug and its effect
55
What are some mechanisms of counterclockwise hysteresis (effect is greater as concentration returns to zero)?
Sensitization (drug activity-induced upregulation of receptors), active agonist metabolites, distribution delay
56
What are some mechanisms of clockwise hysteresis (effect is less as concentration returns to zero)?
Desensitization (drug activity-induced downregulation of receptors), active antagonist metabolites, negative feedback regulation
57
How is clearance related to the volume of distribution and elimination rate constant?
Clearance is the product of Vd and Ke

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