3- Pharmacology fundamentals workshop

Question 1

Compare the apparent Vd for phenobarbital of 0.55L/Kg with that for digoxin (7L/kg).

What does this tell you about the potential movement of these drugs within the body?

Answer 1

7L/kg = high volume of distribution meaning it likes to leave the blood and go into the tissues (Hugh affinity)

want this in an anaesthetic agent (not too strong tho)

Question 2

The half-life for phenobarbital is 100h (in dogs). Another drug X has a half-life of just 5h.
What pharmacokinetic parameter(s) could theoretically be different between the two drugs?

Answer 2

Clearance factor

Question 3

If the half-life of phenobarbital is 76h in dogs. How long will it take to reach the steady state in the dog?

(Steady state is normally achieved within 5 half lives)

Answer 3

76 x 5 = 380hours (15-16days)

Question 4

Why is it common for dose adjustments to have to be made when treating dogs with phenobarbital?

Answer 4

Plasma concentrations dip = were at good levels but now dipped so not therapeutic

> Clearance increased = body gets rid of drug quicker so plasma conc is dipping
- Drug induces expression of liver enzymes (changes clearance)

Question 5

When is steady state normally achieved

Answer 5

within 5 half lives