Distribution Flashcards
Which patient characteristics affect drug distribution?
Oedema and dehydration
Weight loss and obesisty
Gender
Ethnicity
Pregnancy
Age
Health status
How does volume of distribution change with age?
Because volume of water, fat protein, minerals changes with age
describe distribution in relation to blood flow to kidneys, brain, muscle, liver and fat
Kidneys - 22%
Brain - 15%
Muscle - 15%
Liver - 6% systematic 21% GI
Fat - 10%
What does balance depend on?
Relative binding affinity in blood and tissues
Ion trapping in regards to Basic and acidic drugs
Basic drugs accumulate in acidic enviroments
Acidic drugs accumulate in basic enviroments
Define compartment
The sum of all tissues into which a drug dristributes at approximately the same rate
Explain what is meant single by compartment
-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
Explain what is meant by two compartments
- Drug penetrates some tissues rapidly and others slowly
- Combine blood and rapid tissues as as first compartment
-Combine slow tissues as second compartment
What is Volume of Distribution (Vd) definition
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.
Explain Vd in your own terms
Vd is the apparent volume that the drug occupies in the blood
What are the 4 main compartments in which a drug is distributed in?
-Plasma
-Interstitial fluid
-intracellular fluid
-fat
What is a drawback of Vd
Does not give specific information like where the drug is or if it is concentrated in a particular organ
What are the trends foudn in Vd
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
Formula for Vd
Vd = D/C
d - dose
c - concentration
Vd - L/KG
Categorise some drugs with small medium and large Vd
draw a table
Why might a drug be highly distributed into tissues but less so in plasma?
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.
Why might a drug be more concentrated in plasma and less so in tissues?
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
What does Vd tell us?
How much of the drug will stay in the blood and how much will spread out into tissues.
What does a medium Vd imply?
Similar concentration of blood in plasma compared to drug in tissues.
