Drug Distribution

Question 1

Lipid-soluble drugs

Answer 1

bind non-specifically

Question 2

Weak acids

Answer 2

bind to a specific, saturable site

Question 3

Hydrophilic drugs

Answer 3

are highly soluble in aqueous, polar media.

Question 4

Lipophilic drugs

Answer 4

are soluble in fats and non-polar solutions.

Question 5

Many drugs are weak acids or bases

Answer 5

• Ionised:unionised ratio depends on pH

* Ionised drugs have low lipid solubility

Question 6

Blood brain barrier

Answer 6

both a physical and functional barrier

Question 7

Placenta

Answer 7

Tight endothelial cell junctions in maternal and fetal capillaries
Partially protective, except with:
– lipid soluble drugs
– unionised forms of weak acids and bases

Question 8

Chronic abscesses

Answer 8

Avascular tissue compartments

Question 9

Lung infection

Answer 9

Local low PO2 and high PCO2 cause vasoconstriction

Question 10

Extracellular fluid

Answer 10

15 litres

Question 11

plasma

Answer 11

3 litres

Question 12

Interstitial fluids

Answer 12

12 litres

Question 13

Intracellular fluids

Answer 13

27 litres

Question 14

total body water (for a 70kg adult)

Answer 14

42 litres

Question 15

large, water-soluble molecules (e.g. mannitol)

Answer 15

15 litres

Question 16

Highly plasma- bound molecules

Highly charged molecules

Very large
molecules (e.g. heparin

Answer 16

3 litres

Question 17

small, water-soluble molecules (e.g. ethanol)

Answer 17

42 litres

Question 18

Plasma steady state conc. (Css)

The Css value reached depends on:

Answer 18

the rate of drug administered (K0)
divided by
volume of plasma cleared of drug per unit time (CL)

Question 19

The time taken to reach Css depends on:

Answer 19

elimination half-life (t1/2)

Question 20

The apparent volume of distribution (Vd) of a drug is

Answer 20

total amount of drug in the body
divided by
blood plasma concentration of drug

Question 21

Vd varies with:

Answer 21

– Height
–Weight
–Age
–Fluid accumulation 
• ascites
• oedema
• pleural effusion
–Accumulation of fat