5. Distribution

Question 1

Distribution

Answer 1

The reversible transfer of a drug between compartments

Plasma — interstitial fluid —Intracellular fluid

All 3 are compartments: defined volume of body fluids

Question 2

Distribution depends on _______ and ______ of the drug.

Answer 2

Molecular size, polarity/Lipophilicity

Question 3

Very large drugs

Answer 3

Confined to circulation, cannot escape pores

Question 4

Lipophillic drugs

Answer 4

Enriched in fat, can escape circulation

Question 5

Very polar Drugs

Answer 5

Hydrophilic - with a charge can escape circulation but do not cross cell membrane because of polarity

Question 6

Drug evenly distributed

Answer 6

Uncommon

Question 7

Vd - Volume of distribution

Answer 7

Vd= total amount of drug in body/ concentration of drug in plasma

Expressed in liters

High Vd = low concentration in plasma, drug in tissue

Low Vd = high concentration in plasma

Question 8

Protein-binding affects drug administration

Answer 8

Protein bound fraction is not available for action

Ex: albumin: certain number of passengers to transport drug, drug can jump off

Question 9

Drugs may compete for plasma protein binding

Answer 9

Creates drug-drug interaction if drug 2 significantly displaces drug 1s free concentration that drug 1 levels may now be toxic

Question 10

Blood-Brain Barrier

Answer 10

Prevents distribution of many drugs to the brain

P-glycoproteins in BBB

Certain drugs need to be given intrathecally (through spinal cord) to reach brain

Question 11

Drugs may be stores in tissues (fat and bone)

Answer 11

Adipose (fat): drug dosing in obese patients difficult because drug can hide out in fate

Teeth (bone): avoid tetracycline antibiotics in children over 8, it can stain teeth.