Distribution

Question 1

Which patient characteristics affect drug distribution?

Answer 1

Oedema and dehydration
Weight loss and obesisty
Gender
Ethnicity
Pregnancy
Age
Health status

Question 2

How does volume of distribution change with age?

Answer 2

Because volume of water, fat protein, minerals changes with age

Question 3

describe distribution in relation to blood flow to kidneys, brain, muscle, liver and fat

Answer 3

Kidneys - 22%
Brain - 15%
Muscle - 15%
Liver - 6% systematic 21% GI
Fat - 10%

Question 4

What does balance depend on?

Answer 4

Relative binding affinity in blood and tissues

Question 5

Ion trapping in regards to Basic and acidic drugs

Answer 5

Basic drugs accumulate in acidic enviroments

Acidic drugs accumulate in basic enviroments

Question 6

Define compartment

Answer 6

The sum of all tissues into which a drug dristributes at approximately the same rate

Question 7

Explain what is meant single by compartment

Answer 7

-All tissues are penetrated rapidly or not at all
-Drug is assumed to spread instantly throughout all of this space
-This is called the first compartment

Question 8

Explain what is meant by two compartments

Answer 8

• Drug penetrates some tissues rapidly and others slowly
• Combine blood and rapid tissues as as first compartment
  -Combine slow tissues as second compartment

Question 9

What is Volume of Distribution (Vd) definition

Answer 9

The apparent volume of distribution is the amount of theoretical fluid that would be required to contain the drug in the body fluids (intracellular, iterstitial fluid and plasma) at the same concentration as in the plasma.

Question 10

Explain Vd in your own terms

Answer 10

Vd is the apparent volume that the drug occupies in the blood

Question 11

What are the 4 main compartments in which a drug is distributed in?

Answer 11

-Plasma
-Interstitial fluid
-intracellular fluid
-fat

Question 12

What is a drawback of Vd

Answer 12

Does not give specific information like where the drug is or if it is concentrated in a particular organ

Question 13

What are the trends foudn in Vd

Answer 13

Changes in the drug concentration in plasma are proprtional to changes in the drug concentration in tissue
-however this does not mean concentration in plasma is the same as concentration in tissue

Question 14

Formula for Vd

Answer 14

Vd = D/C

d - dose
c - concentration
Vd - L/KG

Question 15

Categorise some drugs with small medium and large Vd

Answer 15

draw a table

Question 16

Why might a drug be highly distributed into tissues but less so in plasma?

Answer 16

This is because the drug has a high Vd. The drug is widley distributed and/or has extensive tissue binding meaning most of the drug is moved out into tissues and less of the drug remains in plasma.

Question 17

Why might a drug be more concentrated in plasma and less so in tissues?

Answer 17

This is becasue the drug has a small Vd. The drug is mostly bound to proteins in the plasma and so does not move out into tissues

Question 18

What does Vd tell us?

Answer 18

How much of the drug will stay in the blood and how much will spread out into tissues.

Question 19

What does a medium Vd imply?

Answer 19

Similar concentration of blood in plasma compared to drug in tissues.