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CMOD Block 2 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What does drug clearance tell you?

A

it describes the body’s efficiency of drug removal (theoretical volume of fluid from which a drug is removed per unit time)

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2
Q

What is the equation for drug clearance (CL)?

A

CL= rate of elimination/concentration

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3
Q

In order to maintain a steady-state concentration of a drug within the therapeutic window, what must a physician do?

A

administer the drug at the same rate that it is eliminated

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4
Q

What is the equation for rate of elimination from an organ?

A

Rate of elimination= Q(Ca-Cv)

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5
Q

What is the value “Q” in the rate of elimination equation?

A

Q= blood flow to the organ

*this is the LIMITING VARIABLE

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6
Q

What is the value “Ca-Cv” in the rate of elimination equation?

A

it is the concentration gradient of drug from the arterial side to the venous side

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7
Q

What concentration do you divide the rate of elimination by to get the clearance?

A

Ca (concentration on the arterial side)

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8
Q

What is the extraction ratio?

A

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

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9
Q

What is the mathematical representation of the extraction ratio(E)?

A

E=(Ca-Cv)/Ca

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10
Q

What is another way to calculate clearance?

A

CL= Q*E

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11
Q

True or false: most drugs obey second order kinetics.

A

FALSE: most drugs obey first order kinetics

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12
Q

What does a concentration versus time plot look like for first order kinetics?

A

exponential decay function

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13
Q

How do you get a “straight line” from a graph of first order kinetics?

A

make Y axis (concentration) a log

keep X axis linear

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14
Q

What does the slope of a first order kinetics reaction (straight line type) tell you?

A

elimination rate constant (Ke)- means that constant FRACTION of the drug is eliminated per unit time
Ex. every 2 hours the concentration is halved (hour0=8, hour2=4, hour4=2, hour6=1)

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15
Q

The absolute amount of drug removed per unit time (in first order kinetics) depends on what factor?

A

concentration

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16
Q

What does half-life mean in first order kinetics?

A

the time it takes for the plasma concentration or the amount of drug in the body to be reduced by 50%

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17
Q

What is another name for 0 order kinetics?

A

saturation kinetics

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18
Q

True or false: few drugs obey zero order kinetics.

A

True

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19
Q

List examples of drugs that obey zero order kinetics.

A

Ethanol
Aspirin
Heparin

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20
Q

What does a concentration versus time plot look like for zero order kinetics?

A

a straight line

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21
Q

True or false: zero order kinetics uses saturable enzymes that make an early plateau in activity.

A

FALSE: zero order kinetics uses enzymes that get saturated at usual levels of drug in the body. The SAME amount of drug is metabolized regardless of the level of drug

22
Q

True or false: half life of drugs in zero order kinetics varies with the DOSE of the drug.

A

TRUE: the larger the dose, the longer the half life

23
Q

What is the volume of distribution?

A

fluid volume that would be required to contain all of the dose at the same concentration as exists in the blood or plasma

24
Q

What is the equation for the volume of distribution?

A

Vd= amount of drug in body/C (blood concentration)

25
Q

What drug has a Vd very close to plasma (~4L)?

A

indocyanine green

26
Q

What drug has a Vd very close to total body water (~40L)?

A

ethanol

27
Q

What drug has a Vd very close to extracellular fluid (~12L)?

A

aspirin

28
Q

What is the equation for elimination rate?

A

Ke= CL/Vd

29
Q

What is the equation for elimination half life?

A

T1/2= 0.7/Ke or 0.7(Vd)/CL

30
Q

True or false: the greater the clearance, the longer the halflife.

A

FALSE: the greater the clearance, the shorter the half-life

31
Q

True or false: if a drug has a large volume of distribution, it will have a longer halflife.

A

True!

32
Q

Drugs with short half-lives are ideally given by what route of administration?

A

IV or sustained release tablets

33
Q

What does half-life help a physician decide?

A 
Dosing interval (drugs often given at half-life intervals)
Dose
34
Q

What is a one compartment open model good to model?

A

drugs that are distributed fairly uniformly throughout the body (because it assumes the entire body is a 1 compartment, open system)

35
Q

What type of kinetics does a one compartment open model follow?

A

first order kinetics (linear decrease)

36
Q

What does a two compartment open model assume?

A
  • drug is in a particular compartment

- equilibrium exists between the blood and other areas

37
Q

What are the “phases” of a two compartment open model?

A

distribution phase: drug drops in blood rapidly when first administered
elimination phase: drug follows first order kinetic model (linear)

38
Q

What do multicompartment models measure?

A

area under the curve

39
Q

What is the relationship between clearance and area under the curve?

A

CL= dose/AUC

40
Q

What is the equation for dosing rate?

A

Dosing Rate= CL * Css
OR
Dosing rate= Dose/dosing interval (T)

41
Q

What is Css?

A

steady-state concentration of the drug (plateau)

42
Q

How is the dosing rate equation modified to account for the loss of drug?

A 
incorporate bioavailability (F)
Dosing rate= (CL * Css)/F
43
Q

What is the “plateau principle”?

A

The plateau principle says that the time to steady state is independent of dose or dosing interval. It is strictly dependent on half-life

44
Q

Around how many half-lives does it take to reach steady state?

A

4-5

45
Q

What is the equation of Css considering dose and dosing rate?

A

Css= (FDose)/(CLT)

46
Q

What is the Css equation for an IV infusion?

A

Css= infusion rate/total body clearance

47
Q

How long does it take an IV infused to reach steady state?

A

around 5 half-lives (not different)

48
Q

When should you use a loading dose?

A

when you cannot wait 5 half-lives to achieve therapeutic range

49
Q

What is the equation for a loading dose?

A

LD= (Css*Vd)/F

50
Q

What is a maintenance dose?

A

dose given after a loading dose that helps maintain the Css in a desired therapeutic window

51
Q

What is the equation for the dosing rate of a maintenance dose?

A

Dosing rate= (target Css* CL)/F

CMOD Block 2 (11 decks)

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