Pharmacodynamics and Receptor Theory MCQ — NEET PG Practice Question | NEETPGAI
Pharmacodynamics and Receptor Theory
medium
pill Pharmacology
All of the following are true regarding dose-response curves and pharmacodynamic principles EXCEPT:
A. Efficacy and potency are synonymous terms; both describe the ability of a drug to produce a response at a given dose
B. The slope of the dose-response curve (Hill coefficient) reflects the degree of cooperativity; a slope > 1 indicates positive cooperativity and a slope < 1 indicates negative cooperativity
C. A drug with a lower EC₅₀ is more potent than a drug with a higher EC₅₀ when compared at the same receptor
D. The EC₅₀ (half-maximal effective concentration) is the ligand concentration that produces 50% of the maximum response and is a measure of agonist potency
Explanation
Dose-Response Curves: Potency vs. Efficacy
Key Point
Potency and efficacy are distinct pharmacodynamic properties. Conflating them is a common and high-yield exam trap.
Definitions and Distinctions
Table
Property
Definition
Measure
Clinical Relevance
Potency
Concentration (or dose) required to produce a given effect
EC₅₀ (lower = more potent)
Determines how much drug is needed; affects dosing frequency
Efficacy
Maximum response (Emax) a drug can achieve, regardless of dose
Intrinsic activity (0–1)
Determines whether the drug can produce the desired therapeutic outcome
High-YieldNEET PG
A drug can be potent but have low efficacy (e.g., partial agonist) or weak but have high efficacy (e.g., full agonist requiring higher doses). These are independent properties.
Why Option 4 Is Wrong
Option 4 incorrectly states that potency and efficacy are synonymous. They are not:
Potency = EC₅₀ (position of curve on x-axis)
Efficacy = Emax (height of curve on y-axis)
Clinical Pearl
Morphine (high potency, high efficacy) vs. aspirin (low potency, moderate efficacy) — morphine works at lower doses but both can produce strong effects. Conversely, a partial agonist may have high potency (low EC₅₀) but low efficacy (cannot reach 100% response).
Correct Statements Explained
Option 1: EC₅₀ is the concentration producing 50% Emax; it inversely reflects potency (lower EC₅₀ = higher potency). ✓
Option 2: Lower EC₅₀ = higher potency; the drug achieves the same response at a lower concentration. ✓
