Pharmacokinetics

Question 1

A drug has a volume of distribution of 0.35 L/kg. In a 70-kg patient, what IV loading dose must be administered to achieve a plasma concentration of 8 mg/L?

Answer 1

196 mg

loading dose= (Vd x desired Cp)/ bioavailability

Question 2

_______ describes the relationship between the administered dose of a drug and the plasma concentration that results

Answer 2

Volume of distribution

Question 3

________ is a measure of an amount of drug in a given volume.

Answer 3

Concentration

Question 4

When is a drug in its most concentrated form?

Answer 4

before we administer it

Question 5

The higher the Vd, the ____________ that must be given to achieve its effect.

Answer 5

the higher the loading dose

Question 6

A drug with a Vd that exceeds total body water(>0.6 L/kg or >42 L) is assumed to be

Answer 6

liphophilic

Question 7

A drug with a Vd that is less than total body water is assumed to be

Answer 7

hydrophilic

Question 8

What is the volume of distribution equation?

Answer 8

Vd= amount of drug/desired plasma concentration

Question 9

Volume of distribution must assume two things:

Answer 9

the drug distributes instantaneously
the drug is not subjected to biotransformation or elimination before it fully distributes

Question 10

Total body water in a 70 kg patient is

Answer 10

42 L

Question 11

Extracellular fluid in a 70 kg patient is

Answer 11

14 L

Question 12

Intracellular fluid in a 70 kg patient is

Answer 12

28 L

Question 13

What patient characteristics affect volume of distribution?

Answer 13

pregnancy & burns

Question 14

What drug characteristics affect volume of distribution?

Answer 14

molecular size, ionization, & protein binding

Question 15

Liphophilic means that

Answer 15

it distributes into the total body water as well as into the fat

Question 16

Liphophilic requires a ______ dose to achieve a given plasma concentration

Answer 16

higher

Question 17

Hydrophilic means that a drug

Answer 17

distributes into some or all of the body water but it does not distribute into fat

Question 18

What is the loading dose equation?

Answer 18

loading dose= Vd x (desired plasma concentration/bioavailability)

Question 19

For an IV medication, bioavailability is equal to

Answer 19

1 since it’s injected directly into the bloodstream

Question 20

The higher the volume of distribution, the __________ the loading dose that must be given to achieve the predetermined plasma concentration.

Answer 20

higher

Question 21

How much water does the plasma volume contain?

Answer 21

4 L

Question 22

How much water does the interstitial fluid contain in a 70 kg patient?

Answer 22

10 L

Question 23

Clearance is directly proportional to:
a. blood flow to clearing organ
b. half-life
c. extraction ratio
d. concentration in the central compartment

Answer 23

A & C

Question 24

Clearance is the

Answer 24

volume of plasma that is cleared of drug per unit time

Question 25

Clearance is directly proportional to

Answer 25

blood flow to the clearing organ, extraction ratio, and drug dose

Question 26

Clearance is inversely proportional to

Answer 26

half-life and drug concentration in the central compartment

Question 27

To maintain a steady-state concentration in the plasma, the infusion rate or dosing interval must

Answer 27

equal the rate of drug clearance

Question 28

As a general rule, steady-state is achieved after

Answer 28

five half-times

Question 29

If a drug has a long half-life, you can achieve steady state faster by

Answer 29

administering a loading dose

Question 30

The most important clearing organs include

Answer 30

liver, kidney, organ independent (Hofmann elimination and ester hydrolysis in the plasma)

Question 31

Steady-state occurs when the

Answer 31

amount of drug entering the body is equivalent to the amount of drug eliminated from the body-there is a stable plasma concentration

Question 32

The plasma concentration curve in a two compartment model illustrates the

Answer 32

biphasic decrease of a drug’s plasma concentration after a rapid IV bolus

Question 33

The alpha phase of a plasma concentration curve represents

Answer 33

distribution from the central compartment (the plasma) to the peripheral compartment (the tissues)

Question 34

The beta phase of a plasma concentration curve represents

Answer 34

elimination from the central compartment

Question 35

A rate constant describes the

Answer 35

speed at which a reaction occurs (or how fast a molecule moves between compartments)

Question 36

Most of the drugs we administer follow a ________ model

Answer 36

multi-compartment model (3 or more)

Question 37

The steeper the slope of line A on a plasma concentration curve, the more _____ the drug is

Answer 37

liphophilic the drug is & the large the volume of distribution

Question 38

The relatively flatter slope (beta phase) of the plasma concentration curve represents

Answer 38

drug elimination from the central compartment

Question 39

Describe K12

Answer 39

the rate constant for drug transfer from the central to the peripheral compartment

Question 40

Describe K21

Answer 40

the rate constant for drug transfer from the peripheral to the central compartment

Question 41

Describe ke

Answer 41

the rate constant for drug elimination from the body

Question 42

After administering an IV drug that distributes into a one-compartment model, the patient’s serum contains 6.25% of the original dose. How many half-lives have elapsed?

Answer 42

4

Question 43

Elimination half-life is the

Answer 43

time it takes for 50% of the drug to be eliminated from the body after a rapid IV injection

Question 44

Elimination half-time is the time

Answer 44

it takes for 50% of the drug to be removed from the plasma during the elimination phase

Question 45

By convention, we say that a drug is cleared from the body when

Answer 45

96.9% of the dose has been eliminated from the plasma

Question 46

The concept of context-sensitive half-time takes the

Answer 46

duration of drug administration into account
it’s the time required for the plasma concentration to decline by 50% after the infusion is stopped

Question 47

The half-time measures a ________ and NOT a _________

Answer 47

constant fraction and not a constant amount

Question 48

The concept of half-times is really only applicable to drugs that follow

Answer 48

a one-compartment model

Question 49

In order of longest, what is the context sensitive half-time of the four main opioids?

Answer 49

fentanyl, alfentanil, sufentanil, remifentanil

Question 50

What is the “context” in context-sensitive half-time?

Answer 50

duration of infusion (time)

Question 51

Which opioid has a similar context-sensitive half-time regardless of infusion duration?

Answer 51

remifentanil