Pharmacology Pharmacokinetic Principles 3 — Questions and Answers
Question 1: Which process describes passive movement of a drug from an area of high concentration to low concentration across a membrane without energy expenditure?
- Active transport
- Facilitated diffusion
- Passive diffusion (Correct answer)
- Pinocytosis
Correct answer: Passive diffusion
Passive diffusion is the most common mechanism of drug absorption and requires no energy, driven solely by concentration gradients.
Question 2: A drug is 90% plasma protein-bound. If a second drug displaces it, which fraction of the drug becomes pharmacologically active?
- 90%
- 10%
- The free (unbound) fraction (Correct answer)
- The bound fraction
Correct answer: The free (unbound) fraction
Only the free (unbound) fraction of a drug is pharmacologically active and able to exert effects at target sites.
Question 3: What does zero-order kinetics mean in drug elimination?
- A constant fraction of drug is eliminated per unit time
- A constant amount of drug is eliminated per unit time (Correct answer)
- Elimination depends on renal function only
- The drug accumulates without any elimination
Correct answer: A constant amount of drug is eliminated per unit time
Zero-order kinetics means a fixed amount (not fraction) of drug is eliminated per unit time, regardless of plasma concentration.
Question 4: Which of the following drugs is most likely to have unpredictable toxicity if renal function declines?
- Propranolol (hepatically cleared)
- Digoxin (renally cleared) (Correct answer)
- Lidocaine (hepatic metabolism)
- Diazepam (hepatic conjugation)
Correct answer: Digoxin (renally cleared)
Digoxin is predominantly renally eliminated, so reduced GFR leads to drug accumulation and potential toxicity.
Question 5: The area under the plasma concentration-time curve (AUC) is a measure of:
- Peak drug concentration
- Total drug exposure over time (Correct answer)
- Rate of drug absorption
- Volume of distribution
Correct answer: Total drug exposure over time
AUC represents total systemic drug exposure integrated over time and is used to assess bioavailability and calculate clearance.
Question 6: A loading dose is used clinically to:
- Reduce the half-life of a drug
- Rapidly achieve therapeutic plasma concentrations (Correct answer)
- Decrease volume of distribution
- Prolong steady-state duration
Correct answer: Rapidly achieve therapeutic plasma concentrations
A loading dose achieves therapeutic concentrations quickly without waiting for 4-5 half-lives of accumulation.
Question 7: Enterohepatic recirculation of a drug leads to:
- Decreased oral bioavailability
- Prolonged drug action due to reabsorption from the gut (Correct answer)
- Accelerated renal elimination
- Reduced volume of distribution
Correct answer: Prolonged drug action due to reabsorption from the gut
Enterohepatic recirculation involves biliary excretion and intestinal reabsorption, prolonging the drug's effect and half-life.
Pharmacology Pharmacokinetic Principles 3
Which process describes passive movement of a drug from an area of high concentration to low concentration across a membrane without energy expenditure?