Volume of distribution

Question 1

Why can the volume of distribution only be determined from plasma concentration after Intravenous drug administration?

Answer 1

Because we need to know the actual dose of drug that reached the circulation i.e. this is the only way we can assure 100% bioavailability

Question 2

Why is volume of distribution an apparent volume?

Answer 2

Because V assumes that drug concentrations are homogenous throughout the body. This is not true, at equilibrium, the concentration of drug is proportional between blood, and different tissues

Question 3

Name 4 reasons why drug concentration is not homogenous throughout the body

Answer 3

1. ) Tissues have different characteristics e.g. fat content, blood perfusion
2. ) Drugs have different physiochemical properties that might make it easier to cross membranes in some tissues more than others
3. )Tissues possess different transporters which might help drugs to cross their membranes
4. ) Plasma and tissue binding of drugs

Question 4

If the fraction unbound in plasma INCREASE, does the volume of distribution increase or decrease?

Answer 4

Increase

Question 5

If the fraction unbound in tissue INCREASES, does the volume of distribution increase or decrease?

Answer 5

Decrease

Question 6

When in a hospital setting would you give a loading dose?

Answer 6

When you need to achieve steady state quickly i.e. you can’t wait 5 half lives to reach the therapeutic dose.

Question 7

If a drug is given intravenously, what is F?

Answer 7

1 = 100% bioavailability