Pharm.D. Doctor of Pharmacy Pharmacokinetics and Pharmacodynamics 1 — Questions and Answers
Question 1: Which pharmacokinetic parameter describes the volume of plasma cleared of a drug per unit time?
- Clearance (Correct answer)
- Volume of distribution
- Half-life
- Bioavailability
Correct answer: Clearance
Clearance (CL) is the pharmacokinetic parameter that represents the volume of plasma cleared of a drug per unit time, typically expressed in L/hr or mL/min.
Question 2: A drug has a half-life of 6 hours. Approximately how long does it take to reach steady-state concentration?
- 6 hours
- 12 hours
- 24–30 hours (Correct answer)
- 48 hours
Correct answer: 24–30 hours
Steady state is reached after approximately 4–5 half-lives, so a drug with a 6-hour half-life reaches steady state in about 24–30 hours.
Question 3: Which of the following best defines the volume of distribution (Vd)?
- The rate at which drug is eliminated
- A proportionality constant relating plasma concentration to total drug in the body (Correct answer)
- The fraction of drug absorbed systemically
- The time to reach maximum plasma concentration
Correct answer: A proportionality constant relating plasma concentration to total drug in the body
Volume of distribution is an apparent proportionality constant that relates the total amount of drug in the body to the measured plasma concentration.
Question 4: What is the effect of first-pass metabolism on oral bioavailability?
- Increases bioavailability
- Has no effect on bioavailability
- Decreases bioavailability (Correct answer)
- Only affects IV bioavailability
Correct answer: Decreases bioavailability
First-pass (hepatic) metabolism reduces oral bioavailability by metabolizing a significant fraction of the drug before it reaches systemic circulation.
Question 5: Which pharmacodynamic concept describes the relationship between drug concentration and the maximum possible effect?
- EC50
- Emax model (Correct answer)
- Therapeutic index
- Zero-order kinetics
Correct answer: Emax model
The Emax model describes the relationship between drug concentration and effect, where Emax is the maximum achievable pharmacological response.
Question 6: A drug following zero-order kinetics is eliminated at:
- A rate proportional to its concentration
- A constant amount per unit time (Correct answer)
- A rate proportional to the square of its concentration
- A rate that doubles with each dose
Correct answer: A constant amount per unit time
Zero-order kinetics means a constant amount of drug is eliminated per unit time regardless of concentration, as seen with ethanol and phenytoin at high doses.
