Drug distribution

Question 1

What factors affect the distribution of drugs?

Answer 1

Perfusion of each organ
Permeability of tissue membranes
Physiochemical properties of the drug
Binding of drugs to plasma and tissue components and partitioning into phospholipids

Question 2

Amount of drug (mg) = ? x ?

Answer 2

volume of distribution (L) x Concentration (mg/L)

Question 3

Why does the volume of distribution vary so much?

Answer 3

Drugs can bind to plasma proteins, blood cells and tissue components:

• Acidic drugs have a strong affinity for plasma proteins i.e. small vd
• Basic drugs have a strong affinity for acidic phospholipids in tissues i.e high vd
• Monoclonal antibodies tend to reside in plasma

Question 4

Where are the locations of distribution barriers?

Answer 4

BBB - barrier at capillary level

Kidneys, muscle - barrier at cellular level