Pharmacology Pharmacodynamics 2 — Questions and Answers
Question 1: A drug that binds to a receptor and produces a submaximal response even at full receptor occupancy is called a:
- Full agonist
- Partial agonist (Correct answer)
- Competitive antagonist
- Inverse agonist
Correct answer: Partial agonist
A partial agonist has intrinsic efficacy between 0 and 1, so it cannot produce the maximal response even when all receptors are occupied.
Question 2: Which pharmacodynamic parameter describes the concentration of drug required to produce 50% of the maximum effect?
- Emax
- EC50 (Correct answer)
- Kd
- Hill coefficient
Correct answer: EC50
EC50 (effective concentration 50%) is the drug concentration that produces 50% of the maximal response and is used as a measure of drug potency.
Question 3: An inverse agonist differs from a competitive antagonist in that it:
- Blocks receptor access by the endogenous ligand
- Produces the opposite effect to the agonist by stabilizing the inactive receptor state (Correct answer)
- Irreversibly binds the receptor
- Increases the potency of the agonist
Correct answer: Produces the opposite effect to the agonist by stabilizing the inactive receptor state
An inverse agonist has negative intrinsic efficacy, stabilizing the inactive conformation of the receptor and producing an effect opposite to the agonist.
Question 4: Tachyphylaxis is best defined as:
- Increased drug response after repeated dosing
- Rapid decrease in response to a drug after repeated administration in a short time (Correct answer)
- Slow development of tolerance over weeks
- Cross-reactivity between structurally similar drugs
Correct answer: Rapid decrease in response to a drug after repeated administration in a short time
Tachyphylaxis is a rapid, short-term reduction in drug response that occurs after repeated or continuous exposure to a drug.
Question 5: Which statement correctly describes a quantal dose-response relationship?
- It measures the magnitude of effect in a single individual
- It describes the frequency of a defined all-or-none response in a population (Correct answer)
- It is identical to the graded dose-response curve
- It measures receptor binding affinity
Correct answer: It describes the frequency of a defined all-or-none response in a population
Quantal dose-response curves plot the percentage of a population exhibiting a defined all-or-none endpoint (e.g., death, sleep, seizure) against drug dose.
Question 6: The therapeutic index is calculated as:
- ED50 / LD50
- LD50 / ED50 (Correct answer)
- TD50 / EC50
- Emax / EC50
Correct answer: LD50 / ED50
The therapeutic index = LD50 / ED50; a higher ratio indicates a greater margin of safety between the effective and lethal doses.
Question 7: Receptor downregulation in response to prolonged agonist exposure typically results in:
- Sensitization to the drug
- Decreased drug response over time (Correct answer)
- Increased receptor affinity
- Enhanced second-messenger signaling
Correct answer: Decreased drug response over time
Prolonged agonist exposure causes receptor internalization and degradation (downregulation), reducing the number of available receptors and diminishing drug effect.
Pharmacology Pharmacodynamics 2
A drug that binds to a receptor and produces a submaximal response even at full receptor occupancy is called a: