L5 Pharmacokinetics II

Question 1

What does a large Vd mean?

Answer 1

The drug get distributed to peripheral tissues beyond the plasma

Question 2

What does a small Vd mean?

Answer 2

It means that the drug stays mostly in the blood

Question 3

As plasma levels of a drug fall, what happens to the drug that went into the storage depots (fat, tissues, bone, transcellular)?

Answer 3

They come out of their storage depots, down their concentration gradients and into the plasma.

Question 4

What kind of drugs accumulate in the fat?

Answer 4

Highly lipid soluble drugs like anesthetics

Question 5

What kinds of drugs accumulate in bone?

Answer 5

Cheating drugs like tetracyclines

Question 6

If a drug has a high plasma protein binding, what does its Vd probably look like?

Answer 6

It probably has a low Vd, meaning it accumulates in plasma

Question 7

What does plasma protein binding do to a drug’s half life?

Answer 7

Prolongs it

Question 8

How do you calculate Vd?

Answer 8

Vd= Total dose of drug given/plasma concentration

Question 9

Is the fetus acidic or basic compared to the mother?

Answer 9

Acidic. Basic drugs will get trapped

Question 10

IS Breast milk more acidic or basic than plasma?

Answer 10

More acidic

Question 11

What kind of drugs get trapped in breaks milk?

Answer 11

Basic and lipid-soluble

Tetracyclines, phenobarbital

Question 12

What are sites of drug exclusion

Answer 12

Sites where drugs would have to be injected in order to get to those spaces.
Ex: CSF, ocular fluid, fetal fluid, pleural fluid

Question 13

How are most drugs eliminated

Answer 13

1st order

Question 14

What is first-order elimination?

Answer 14

Percentage of the drug eliminated/time

Depends on plasma concentration

Question 15

Why would we plot the elimination of a first-order drug in a semi-logarithmic form?

Answer 15

Gives us a straight line that makes it easy to calculate half life

Question 16

What is half life?

Answer 16

Time required to decrease the plasma concentration by 50%

Question 17

What the half life of a drug with Vd=40L and CL of 5 L/hr?

Answer 17

T 1/2= (0.7 Vd)/CL
= (.7x40)/5
=5.6 hours

Question 18

What is the half life of a drug in an 80kg man if the Vd= 0.57L/Kg and CL=5?

Answer 18

T 1/2= (0.7 x 0.57x80)/5

= 6.4 hr

Question 19

How long do you need to wait to determine Css plasma levels?

Answer 19

About 5 half lives

Question 20

Is the time to reach CSS related to the size of the dose you gave them?

Answer 20

NO it is only related to half life

Remember
Half life= (0.7 x Vd)/CL

Question 21

Shortening the dosing internal or increasing the dose will have what effect on Css?

Answer 21

Increase

Question 22

What is zero-order elimination?

Answer 22

Constant AMOUNT eliminated over unit of time

Question 23

Does half life apply to zero-order elimination?

Answer 23

NO

Question 24

What is the elimination of ethanol?

What kind of elimination is it (1st or 0 order)

Answer 24

10g/hr

Zero order elimination

Question 25

If you plot the elimination of a zero-order drug on a logarithmic scale, what kind of line do you get? Curved or straight

Answer 25

curved

Question 26

If you give a zero order drug repeatedly in high doses, will you develop steady state levels?

Answer 26

No, because its not dependent on plasma levels

Question 27

What happens when you give zero order drugs at higher doses than their elimination rate?

Answer 27

They will accumulate in the body and produce excessive plasma levels and toxicity

Question 28

What is Clearance? CL

Answer 28

The volume of plasma from which a drug is removed per unit of time

Question 29

How do you calculate CL?

Answer 29

CL= Vd x (0.7/half life) | Just flipping around the equation for T 1/2

Question 30

What is the CL of a drug with a Vd=100L and T 1/2=2 hours

Answer 30

CL= (.7 x Vd)/ half life CL=35 L/hr

Question 31

What is the CL if Vd=100: and half life is 2 hours in a 80kg patient?

Answer 31

First you calculate Vd in L/kg Vd=100L/70kg = 1.43 L/kg CL= (.7 x 1.43 x 80)/2 CL=40 L/hr

Question 32

What is the standard weight that Vd’s apply to?

Answer 32

70kg patient

Question 33

How do you calculate CL?

Answer 33

CL= (Vd)(.7/ t 1/2)

Question 34

What 3 things are directly proportional to the Css?

Answer 34

Dose, bioavailability, and T 1/2

Question 35

What 2 things are in the denominator of the Css equation

Answer 35

CL and Vd

Question 36

How many 1/2 lives does it take to reach CSS

Answer 36

5

Question 37

How do you calculate dosing rate/elimination rate?

Answer 37

(CL)(TC) _________ F

Question 38

How do you calculate the maintenance dose?

Answer 38

(Dosing rate)(dosing interval) Remember dosing interval is CL x TC __________ F

Question 39

What is F in the dosing rate calculation if drug is infused?

Answer 39

1 Dosing rate: CL x TC / F

Question 40

How fo you calculate loading dose

Answer 40

LD= Vd x TC

Question 41

Why would you administer a loading dose

Answer 41

To achieve immediate therapeutic plasma concentrations