PEBC Pharmacology Basics 5 — Questions and Answers
Question 1: Renal clearance of a drug is increased when the drug is:
- Highly protein-bound in plasma
- Actively secreted by renal tubules (Correct answer)
- Extensively reabsorbed in the tubule
- Highly lipophilic
Correct answer: Actively secreted by renal tubules
Active tubular secretion adds to glomerular filtration, substantially increasing total renal clearance beyond that predicted by filtration alone.
Question 2: The therapeutic effect of a drug that acts as an enzyme inhibitor is most directly related to:
- Receptor upregulation
- Accumulation of the enzyme's substrate or reduction of its product (Correct answer)
- Increased protein synthesis
- Ion channel blockade
Correct answer: Accumulation of the enzyme's substrate or reduction of its product
Enzyme inhibitors reduce conversion of substrate to product, so substrate accumulates and/or product decreases, which is the basis of the therapeutic effect.
Question 3: Which statement about drug half-life in first-order kinetics is TRUE?
- Half-life increases as plasma concentration increases
- Half-life is independent of the initial dose or concentration (Correct answer)
- Half-life equals the time for 50% receptor occupancy
- Half-life is doubled in zero-order kinetics
Correct answer: Half-life is independent of the initial dose or concentration
In first-order kinetics, half-life is constant (t½ = 0.693/ke) and does not depend on the drug concentration or dose.
Question 4: Upregulation of receptors is most commonly associated with:
- Chronic agonist exposure
- Chronic antagonist exposure (Correct answer)
- CYP enzyme induction
- Increased first-pass metabolism
Correct answer: Chronic antagonist exposure
Prolonged receptor blockade by antagonists leads to receptor upregulation, increasing the number or sensitivity of receptors, which can cause rebound effects if the antagonist is abruptly stopped.
Question 5: Which phase I metabolic reaction is most commonly catalyzed by cytochrome P450 enzymes?
- Glucuronidation
- Sulfation
- Oxidation (Correct answer)
- Acetylation
Correct answer: Oxidation
Oxidation is the predominant phase I reaction and is primarily carried out by cytochrome P450 (CYP) enzymes located mainly in the liver.
Question 6: A patient with severe renal failure is prescribed a drug that is 90% renally excreted unchanged. What is the expected consequence?
- Faster elimination of the drug
- Drug accumulation and increased risk of toxicity (Correct answer)
- Increased hepatic metabolism as compensation
- Decreased volume of distribution
Correct answer: Drug accumulation and increased risk of toxicity
In renal failure, a drug primarily excreted by the kidneys will accumulate because clearance is markedly reduced, increasing the risk of dose-dependent toxicity.
Question 7: Which pharmacokinetic model assumes that the body acts as a single, well-mixed compartment for drug distribution?
- Two-compartment model
- Physiologically based pharmacokinetic (PBPK) model
- One-compartment model (Correct answer)
- Michaelis-Menten model
Correct answer: One-compartment model
The one-compartment model assumes instantaneous and uniform drug distribution throughout the body, simplifying pharmacokinetic calculations.
PEBC Pharmacology Basics 5
Renal clearance of a drug is increased when the drug is: