Sun28November0628PM 50

In a clinical trial of a new intravenous induction agent, the plasma concentrations of this drug are taken at regular time intervals following a bolus.

The following data are acquired:

Time following injection (hours) Plasma concentration (mcg/mL)

2 400

6 100

10 25

14 6.25

From these measurements which one of the following options approximates best to the plasma half life (T½) of the drug?

(Please select 1 option)

10 hours

8 hours

1 hour

2 hours Correct

4 hours

Explanation

The plasma half life (T½) of a drug is the time it takes for the initial plasma concentration to fall by 50%.

Once injected into the central compartment (intravascular space) the concentration of the intravenous induction agent decreases exponentially as it is eliminated and redistributed.

Extrapolating the values from the plasma concentration vs. time data:

Plasma concentration at time zero = 800 mcg/mL

Plasma concentration at 2 hours = 400 mcg/mL

Plasma concentration at 4 hours = 200 mcg/mL

Plasma concentration at 6 hours = 100 mcg/mL

Plasma concentration at 8 hours = 50 mcg/mL

etc.

Answer Statistics

1

3%

2

9%

3

72%

4

18%

Times answered: 247