Pharmacology Pharmacodynamic Mechanisms 2 — Questions and Answers
Question 1: Which term describes a drug that binds to a receptor and produces a submaximal response regardless of dose?
- Full agonist
- Partial agonist (Correct answer)
- Inverse agonist
- Competitive antagonist
Correct answer: Partial agonist
A partial agonist has intrinsic efficacy between 0 and 1, so it cannot produce the maximal response even at receptor saturation.
Question 2: An inverse agonist differs from a neutral antagonist in that an inverse agonist:
- Blocks agonist binding without any effect of its own
- Reduces receptor activity below constitutive baseline (Correct answer)
- Increases receptor affinity for endogenous ligands
- Competes reversibly with agonists at the active site
Correct answer: Reduces receptor activity below constitutive baseline
An inverse agonist stabilizes the inactive receptor conformation, reducing constitutive (basal) receptor activity below the unliganded baseline.
Question 3: The Emax in a dose-response curve represents:
- The dose producing 50% of maximum effect
- The maximum possible effect of a drug (Correct answer)
- The slope of the linear portion of the curve
- The drug concentration at receptor equilibrium
Correct answer: The maximum possible effect of a drug
Emax is the ceiling effect — the greatest response a drug can produce regardless of how much dose is increased.
Question 4: Two drugs are said to be equieffective when they:
- Have the same molecular weight
- Produce the same maximum effect
- Require the same dose to achieve any response (Correct answer)
- Bind to identical receptor subtypes
Correct answer: Require the same dose to achieve any response
Equieffective doses produce the same magnitude of response and are the basis for comparing drug potency.
Question 5: Receptor reserve (spare receptors) means that:
- Extra receptors are stored intracellularly until needed
- Maximum effect is achieved before all receptors are occupied (Correct answer)
- Agonist affinity exceeds its intrinsic efficacy
- Spare receptors have lower affinity than occupied ones
Correct answer: Maximum effect is achieved before all receptors are occupied
When receptor reserve exists, the system reaches Emax while a fraction of receptors remains unoccupied, allowing the drug to appear more potent than its Kd would predict.
Question 6: Which pharmacodynamic parameter is most affected when a competitive antagonist is present?
- Emax of the agonist
- EC50 of the agonist (Correct answer)
- Hill coefficient of the agonist
- Intrinsic efficacy of the agonist
Correct answer: EC50 of the agonist
A competitive antagonist shifts the agonist dose-response curve rightward, increasing EC50, while Emax remains achievable with higher agonist concentrations.
Question 7: The phenomenon where prolonged receptor activation leads to decreased receptor number on the cell surface is called:
- Sensitization
- Tachyphylaxis
- Receptor downregulation (Correct answer)
- Supersensitivity
Correct answer: Receptor downregulation
Downregulation involves internalization and degradation of receptors following sustained agonist exposure, reducing overall cellular responsiveness.
Pharmacology Pharmacodynamic Mechanisms 2
Which term describes a drug that binds to a receptor and produces a submaximal response regardless of dose?