Drug Distribution- Vd

Question 1

Define vd

Answer 1

Apparent volume into which a drug disperses in order to produce the observed plasma concentration

Question 2

How to calculate vd?

Answer 2

Total amount of drug in body/ plasma concentration of drug

Question 3

Unit for plasma concentration of drug

Answer 3

g/L

Question 4

If a drug remains in the plasma, what will happen to vd / drug dose?

Answer 4

Vd will be low
Drug dose will be low

Question 5

If a drug disperses to other fluids or tissues, what will happen to vd / drug dose?

Answer 5

Vd will be high
Drug dose needs to be high

Question 6

Vd is a theoretical number to help describe what?

Answer 6

How well drugs distribute, rather than an actual real-life volume

Question 7

Calculate Total amount of drug

Answer 7

Plasma concentration drug (mg/L) x vd

Question 8

How does protein binding affect vd?

Answer 8

Bound drugs can’t leave the circulatory system
Higher proportion remains in the plasma
Therefore, total plasma concentration will be higher
Vd will be lower

Question 9

Drug factors affecting vd?

Answer 9

Plasma protein binding
Tissue binding
Physiochemical properties of a drug: size, charge, pKa, lipid/water solubility

Question 10

Patient factors affecting vd?

Answer 10

Age, sex, body musculfat proportion, level of hydration,water distribution (oedema, effusions pregnancy)

Question 11

Increasing drug dose by 10% will have what impact on plasma levels?

Answer 11

Small

Question 12

If medication stopped what effect will this have on vd?

Answer 12

Takes longer for plasma levels to fall, there is a reservoir elsewhere in the body