OSCE Pharmacology Fundamentals 3 — Questions and Answers
Question 1: A competitive antagonist is given alongside an agonist. What happens to the agonist's dose-response curve?
- Shifts to the right with the same maximum effect (Correct answer)
- Shifts to the right with a reduced maximum effect
- Shifts to the left with an increased maximum effect
- Remains unchanged
Correct answer: Shifts to the right with the same maximum effect
A competitive antagonist shifts the agonist dose-response curve to the right (higher EC50) but the maximum effect is preserved if enough agonist is available.
Question 2: Which pharmacodynamic concept describes a drug that binds a receptor and produces less than the maximum possible effect even at full receptor occupancy?
- Partial agonism (Correct answer)
- Competitive antagonism
- Inverse agonism
- Receptor downregulation
Correct answer: Partial agonism
Partial agonists have intrinsic efficacy less than 1, so they cannot produce the full maximal response even when all receptors are occupied.
Question 3: A patient's renal function declines significantly. Which pharmacokinetic parameter is most directly affected for renally cleared drugs?
- Clearance (Correct answer)
- Volume of distribution
- Protein binding
- Oral bioavailability
Correct answer: Clearance
Renal clearance is directly reduced when GFR falls, leading to drug accumulation and potentially toxicity.
Question 4: Which term describes the minimum concentration of drug needed at the receptor to produce a measurable effect?
- Threshold concentration (Correct answer)
- Maximum efficacy
- Ceiling effect
- Intrinsic activity
Correct answer: Threshold concentration
Threshold concentration is the minimum drug concentration required to elicit a detectable pharmacological response.
Question 5: A patient on a stable dose of theophylline starts smoking. What adjustment is expected?
- Dose increase because smoking induces CYP1A2 and lowers theophylline levels (Correct answer)
- Dose decrease because smoking inhibits theophylline metabolism
- No change because theophylline is renally excreted
- Switch to a different drug class
Correct answer: Dose increase because smoking induces CYP1A2 and lowers theophylline levels
Smoking induces CYP1A2, accelerating theophylline metabolism and reducing its plasma concentration, requiring a higher dose.
Question 6: Which phenomenon describes decreased drug effect over time requiring higher doses to achieve the same response?
- Tolerance (Correct answer)
- Tachyphylaxis
- Sensitization
- Synergism
Correct answer: Tolerance
Tolerance is the gradual decrease in response to a drug with repeated exposure, often due to receptor downregulation or metabolic adaptation.
Question 7: An irreversible antagonist is administered. Which statement correctly describes the resultant dose-response curve of the agonist?
- Maximum effect is reduced and cannot be overcome by increasing agonist dose (Correct answer)
- The curve shifts right but maximum effect is maintained
- EC50 is unchanged but maximum effect increases
- No change occurs because antagonism is competitive
Correct answer: Maximum effect is reduced and cannot be overcome by increasing agonist dose
Irreversible (non-competitive) antagonists permanently occupy receptors, reducing the maximal response regardless of agonist concentration.
OSCE Pharmacology Fundamentals 3
A competitive antagonist is given alongside an agonist.
What happens to the agonist's dose-response curve?