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CMOD/PCM- Block 2 > Pharm: Pharmacokinetics I > Flashcards

Pharm: Pharmacokinetics I Flashcards

1
Q

What is drug clearance (abbrev. CL)?

A

the theoretical volume of fluid from which a drug is removed per unit time

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2
Q

What are the fundamental differences between therapeutic implications of zero-order and first-order elimination kinetics?

A

Zero-order kinetics drugs are metabolized by enzymes, which are saturable RLS, and are metabolized at a constant amount per unit time, thus no plateau observed.
First-order kinetics drugs are metabolized at a constant fraction per unit time (half-life) and will show a plateau.

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3
Q

What is the concept of apparent volume distribution?

A

the apparent space the drug resides in

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4
Q

What is the concept of elimination half-life? What is its relationship to clearance and volume of distribution?

A

the rate of drug removal

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5
Q

How is elimination half-life calculated mathematically?

A

Ke = CL / Vd

  • Ke is the elimination constant
  • units is 1/min
  • *The change in drug concentration with respect to time is equal to the slope of concentration vs. time plot, or -Ke, or natural log of C/Co = -Ke x t

T1/2= 0.7/Ke

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6
Q

What is the plateau principle, and how is it applied to drug sampling intervals and expected time course of drug in the body?

A

the plateau principle says that the time to steady state is dependent on the half-life; fluctuations will be proportional to the dose interval over the half-life: increasing dose interval will lead to greater fluctuations; decreasing it will lead to increased steady-state concentrations and smaller fluctuations

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7
Q

What are the main reasons to study pharmacokinetics?

A
  1. there is a relationship between concentration of drug (bioavailable) and its effects
  2. to develop a rational framework for dosing
  3. improve therapeutic efficacy by selecting dosing regimens to match patients’ parameters
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8
Q

If a clinician typically wants to maintain steady-state concentrations of a drug within the therapeutic window, how should the drug be administered?

A

At the same rate it’s eliminated

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9
Q

What is the formula for mathematically calculating dosing rate?

A

dosing rate = CL x Css

  • CL = clearance rate
  • Css = [desired] steady-state concentration
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10
Q

What is the formula for mathematically calculating clearance?

A

rate of elimination / concentration

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11
Q

What is the formula for mathematically calculating systemic clearance?

A

CL =CLrenal + CLhepatic + CLother

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12
Q

What is the formula for mathematically calculating rate of drug elimination of an organ?

A 
= Q x Ca - Q x Cv
=Q(Ca-Cv)
*Q = blood flow to the organ
*Ca = arterial drug concentration
*Cv = venous drug concentration
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13
Q

What is the formula for mathematically calculating clearance for an organ?

A 
CLorgan = Q[(Ca-Cv) / Ca] = Q x E
*E = extraction ratio
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14
Q

For drugs handled by the kidney, ____ clearance is most important to watch.

A

renal

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15
Q

What is the limiting variable in drug clearance?

A

blood flow (presentation of drug) to the organ

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16
Q

What is the extraction ratio (E)?

A

the fraction of drug that has been presented on the arterial side that is removed by the organ

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17
Q

On a linear graph of drug concentration over time, how will first- and zero-order kinetic reactions appear?

A

first order = exponential decay

zero order = linear

18
Q

On a graph of log drug concentration over linear time, how will first-order kinetic reactions appear? What does this mean?

A

first order = linear; this means that a constant fraction of the drug will be eliminated per unit time (ex: half-life)

19
Q

Remind me: what is the volume of distribution?

A

the volume of fluid that would be required to contain all of the drug dose at the same concentration as exists in the blood or plasma; Vd = amount of drug in body / blood concentration

20
Q

What is significant about the time at which C0/C = 2?

A

This is the time of the half-life– this formula indicates that the original drug concentration (C0) divided by the current concentration (C) equals 2

21
Q

In the body, a drug’s half life is the time it takes for the concentration of drug in ____ to be reduced by 50%.

A

plasma

22
Q

What is clinical significant about half-life determination?

A
  • to determine the dosing interval
  • to help determine dose
  • may determine route of administration
  • indicates time required to reach steady-state
23
Q

True or false: a drug is usually given at half-life intervals to maintain steady state dosing.

A

True

24
Q

What route of administration might be the best for drugs with short half-lives?

A

intravenous

25
Q

What is a pharmacokinetic model?

A

model used for designing and rationalizing pharmaco-therapy regimens; single-IV dose models are a simple, one-compartment open-system model

26
Q

Two compartment open model for pharmacokinetics assumes that much of a drug is in one particular compartment (often blood) and that an equilibrium exists between what? What happens during and after equilibration?

A

that first particular compartment (often blood) and other areas; as it equilibrates the concentration drops rapidly, following equilibration the concentration follows a first-order model for elimination

27
Q

What model is most realistic for the body?

A

multicompartment models (requires computer assistance); clearance equals the dose divided by the area under the curve (curve of concentration in blood over time)

28
Q

What is the bioavailability term, F, used for?

A

modifying the dosing rate equation to account for variable bioavailability which will affect the dosing rate needed to maintain steady state concentrations; added to formula as follows:
Dosing rate x F = CL x Css

29
Q

About how many half-lives does it take to achieve steady-state?

A

about 4-5

30
Q

Time to steady state is independent of ____ or ____ ____, but strictly dependent on ____.

A

independent of dose or dose interval; dependent on half-life

31
Q

What clinical features will be seen or not seen below the therapeutic range?

A

no clinical benefit will be seen

32
Q

What clinical features will be seen or not seen above the therapeutic range?

A

toxicity may be seen

33
Q

Clinicians can control what aspects of drug administration that will affect the peak/trough and magnitude of the Css?

A

the dosing interval and the dose

34
Q

What formula is used to determine the infusion rate for IV administered drugs?

A

CSS = infusion rate / total body clearance

35
Q

What is the definition of a loading dose?

A

the desired steady state concentration of a drug times the volume of distribution adjusted for bioavailability;

36
Q

Why might loading doses be dangerous?

A

due to the high concentrations that are achieved

37
Q

What is the practice of loading dosing for therapeutic use?

A

administering enough drug to achieve desired Css when one cannot wait for 5 half-lives to achieve a therapeutic range; e.g. in heart attacks, serious heart failure, overwhelming bacterial infections, etc.

38
Q

What is the practice of maintenance dosing for therapeutic use?

A

following the loading dose, drug is given in maintenance doses to keep the drug within the therapeutic window such that:
Dosing rate = (target Css x CL) / F

39
Q

For zero order kinetics drug elimination, Km is used to modify LD, CSS, and DR equations. What is Km?

A

Km is the dose that produces 50% of the maximal elimination rate

40
Q

For zero order kinetics drug elimination, Vm is used to modify LD, CSS, and DR equations. What is Vm?

A

Vm is the maximum rate of the elimination process

41
Q

True or false: Loading doses are calculated in the same way whether the drug obeys zero or first order kinetics.

A

True. The others (DR, CSS) are calculated differently.

CMOD/PCM- Block 2 (41 decks)

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