Flashcards in Pharmacokinetics Deck (51):

1

## What does drug clearance tell you?

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

2

## What is the equation for drug clearance (CL)?

### CL= rate of elimination/concentration

3

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

### administer the drug at the same rate that it is eliminated

4

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

### Rate of elimination= Q(Ca-Cv)

5

## What is the value "Q" in the rate of elimination equation?

###
Q= blood flow to the organ

*this is the LIMITING VARIABLE

6

## What is the value "Ca-Cv" in the rate of elimination equation?

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

7

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

### Ca (concentration on the arterial side)

8

## What is the extraction ratio?

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

9

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

### E=(Ca-Cv)/Ca

10

## What is another way to calculate clearance?

### CL= Q*E

11

## True or false: most drugs obey second order kinetics.

### FALSE: most drugs obey first order kinetics

12

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

### exponential decay function

13

## How do you get a "straight line" from a graph of first order kinetics?

###
make Y axis (concentration) a log

keep X axis linear

14

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

###
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)

15

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

### concentration

16

## What does half-life mean in first order kinetics?

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

17

## What is another name for 0 order kinetics?

### saturation kinetics

18

## True or false: few drugs obey zero order kinetics.

### True

19

## List examples of drugs that obey zero order kinetics.

###
Ethanol

Aspirin

Heparin

20

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

### a straight line

21

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

### 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

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

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

23

## What is the volume of distribution?

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

24

## What is the equation for the volume of distribution?

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

25

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

### indocyanine green

26

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

### ethanol

27

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

### aspirin

28

## What is the equation for elimination rate?

### Ke= CL/Vd

29

## What is the equation for elimination half life?

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

30

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

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

31

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

### True!

32

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

### IV or sustained release tablets

33

## What does half-life help a physician decide?

###
Dosing interval (drugs often given at half-life intervals)

Dose

34

## What is a one compartment open model good to model?

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

35

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

### first order kinetics (linear decrease)

36

## What does a two compartment open model assume?

###
-drug is in a particular compartment

-equilibrium exists between the blood and other areas

37

## What are the "phases" of a two compartment open model?

###
distribution phase: drug drops in blood rapidly when first administered

elimination phase: drug follows first order kinetic model (linear)

38

## What do multicompartment models measure?

### area under the curve

39

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

### CL= dose/AUC

40

## What is the equation for dosing rate?

###
Dosing Rate= CL * Css

OR

Dosing rate= Dose/dosing interval (T)

41

## What is Css?

### steady-state concentration of the drug (plateau)

42

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

###
incorporate bioavailability (F)

Dosing rate= (CL * Css)/F

43

## What is the "plateau principle"?

### 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

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

### 4-5

45

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

### Css= (F*Dose)/(CL*T)

46

## What is the Css equation for an IV infusion?

### Css= infusion rate/total body clearance

47

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

### around 5 half-lives (not different)

48

## When should you use a loading dose?

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

49

## What is the equation for a loading dose?

### LD= (Css*Vd)/F

50

## What is a maintenance dose?

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

51