Key Concepts: Apparent Volume Of Distribution

Question 1

What is volume of distribution? (Vd)

Answer 1

A metaphorical value of how much of a drug partitions between the plasma and tissue

Question 2

What does a high Vd mean?

Answer 2

A high Vd would mean that more of the drug crosses the membrane and leaves the plasma to go into cells

Question 3

What does a low Vd mean?

Answer 3

A low Vd means less of the drug is able to cross the membrane so stays within the bloodstream rather than going into cells

Question 4

What can lower the volume of distribution?

Answer 4

Drugs that exhibit high plasma protein binding can bind to plasma proteins such as albumin and this reduces the availability of the drug to diffuse into target organs, therefore a lower Vd

Question 5

What are some other factors that affect Vd?

Answer 5

-ageing can lower Vd
-obesity can increase Vd
-pathological fluid can increase Vd

Question 6

What is the equation of Vd?

Answer 6

Vd = dose / [drug]plasma