Saudi Prometric Pharmacist Pharmacokinetics and Drug Calculations

Question 1

A drug has a half-life of 6 hours. How long does it take to reach 93.75% of steady-state concentration?

Accepted Answer

24 hours (4 half-lives)

Answer

12 hours (2 half-lives)

Answer

6 hours (1 half-life)

Answer

30 hours (5 half-lives)

Question 2

A drug follows first-order kinetics. If the plasma concentration is 100 mg/L and the half-life is 4 hours, what is the concentration after 12 hours?

Accepted Answer

12.5 mg/L

Answer

25 mg/L

Answer

50 mg/L

Answer

6.25 mg/L

Question 3

What is the clearance (CL) of a drug if the volume of distribution is 42 L and the elimination rate constant (ke) is 0.1 h-1?

Accepted Answer

4.2 L/hr

Answer

0.0024 L/hr

Answer

420 L/hr

Answer

0.42 L/hr

Question 4

A drug's oral bioavailability is 25%. If the IV dose required to produce a therapeutic effect is 100 mg, what oral dose provides the same systemic exposure?

Accepted Answer

400 mg

Answer

25 mg

Answer

40 mg

Answer

250 mg

Question 5

What does a high plasma protein binding (e.g., 99%) of a drug imply about its pharmacokinetics?

Accepted Answer

Only 1% is free (active) drug; small changes in protein binding have large effects on free fraction; displaced drug can cause toxicity

Answer

The drug is widely distributed into tissues

Answer

The drug has high renal clearance

Answer

High protein binding always means long half-life

Question 6

A patient is given 500 mg of drug X intravenously. The initial plasma concentration measured immediately after injection is 10 mg/L. What is the volume of distribution?

Accepted Answer

50 L

Answer

500 L

Answer

5 L

Answer

0.02 L