Half life

Question 1

What is the formula for the elimination half life

Answer 1

T 1/2 = 0.7 * Vd/ Cl

Question 2

What is the relationship between accumulation and elimination in a zero order infusion

Answer 2

Mirror images. After one half life 50% of the drug will be eliminated and 50% accumulated. After 2 half lives 75% will be eliminated and 25% accumulated

Question 3

At how many half lives is >95% of the drug eliminated

Answer 3

4

Question 4

If you are not using a zero order infusion what is the effect on accumulation

Answer 4

Nothing the average accumulation rate is the same as constant infusion however peak concentrations are different

Question 5

What is the accumulation factor

Answer 5

The ratio of the concentration at steady state to the concentration after the first dose at the same time after the dose (e.g. immediately after each respective dose)

Question 6

What are the applications of accumulation/elimination

Answer 6

Time to steady state

Time to eliminate drug (4x elimination half lives)

Question 7

How long is the approximate time to reach peak concentration (Tmax)

Answer 7

Tmax is approx 3 absorption half lives. Because peak concentration is when drug absorption = drug elimination. If drug is completely absorbed 4 half lives) some will have been eliminated.

Question 8

If you give a drug once every half life, what will the concentration be at steady state in relation to the initial concentration after first dose

Answer 8

Twice