Understanding the dose–response relationship is fundamental for B. Pharm students studying pharmacodynamics and therapeutics. This concept explains how varying drug doses influence the magnitude of biological effect, linking potency, efficacy, EC50/ED50 values, and maximal response (Emax). Graded and quantal dose–response curves, receptor occupancy, spare receptors, Hill coefficient, therapeutic index, and safety margin are essential keywords that guide drug selection, dose optimization, and toxicity assessment. Interpreting sigmoidal and log‑dose plots, recognizing competitive versus noncompetitive antagonism, and applying concepts like KD and dose equivalence deepen clinical reasoning and experimental design. Clear mastery of these principles helps predict drug behavior and optimize patient outcomes. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What does EC50 represent in a graded dose–response curve?
- The dose producing 50% of the maximal effect
- The dose lethal to 50% of subjects
- The equilibrium dissociation constant of the drug
- The maximal achievable response
Correct Answer: The dose producing 50% of the maximal effect
Q2. Which term describes the maximum effect a drug can produce regardless of dose?
- Potency
- Therapeutic index
- Efficacy
- EC50
Correct Answer: Efficacy
Q3. How does potency differ from efficacy?
- Potency is the maximal effect; efficacy is the dose to reach it
- Potency refers to the dose required for effect; efficacy is the maximum effect achievable
- They are synonymous
- Potency measures toxicity; efficacy measures safety
Correct Answer: Potency refers to the dose required for effect; efficacy is the maximum effect achievable
Q4. What is a quantal dose–response curve used to determine?
- The graded response magnitude in one individual
- The fraction of a population showing a defined response at different doses
- The receptor binding kinetics of a drug
- The slope of a single-cell response
Correct Answer: The fraction of a population showing a defined response at different doses
Q5. Which parameter is most directly associated with drug safety margin?
- ED50
- Therapeutic index (TI)
- Emax
- EC50
Correct Answer: Therapeutic index (TI)
Q6. How is therapeutic index commonly calculated?
- ED50 divided by LD50
- LD50 divided by ED50
- EC50 multiplied by KD
- Emax divided by potency
Correct Answer: LD50 divided by ED50
Q7. A leftward shift of a log-dose response curve without change in Emax generally indicates:
- Decreased potency
- Increased potency
- Decreased efficacy
- Irreversible antagonism
Correct Answer: Increased potency
Q8. Competitive antagonism typically causes which change on a graded dose–response curve?
- Decrease in Emax with no shift in EC50
- Rightward parallel shift with no change in Emax at high agonist concentrations
- Leftward shift and increased Emax
- Immediate irreversible receptor inactivation
Correct Answer: Rightward parallel shift with no change in Emax at high agonist concentrations
Q9. Noncompetitive (irreversible) antagonists usually produce:
- Only a rightward shift without Emax change
- A decrease in Emax and possible change in slope
- An increase in potency of the agonist
- No effect on dose–response relationship
Correct Answer: A decrease in Emax and possible change in slope
Q10. What does a Hill coefficient (n) greater than 1 suggest about a drug–receptor interaction?
- Independent single-site binding
- Negative cooperativity
- Positive cooperativity or steep slope
- No receptor involvement
Correct Answer: Positive cooperativity or steep slope
Q11. Spare receptors (receptor reserve) explain why:
- Partial agonists always achieve full Emax
- Full response can occur even when not all receptors are occupied
- EC50 equals KD for all drugs
- Antagonists increase Emax
Correct Answer: Full response can occur even when not all receptors are occupied
Q12. Which is TRUE about a partial agonist?
- Has higher efficacy than a full agonist
- Produces lower maximal effect than a full agonist even at full receptor occupancy
- Always acts as an antagonist in all situations
- Has no intrinsic activity
Correct Answer: Produces lower maximal effect than a full agonist even at full receptor occupancy
Q13. ED50 in a quantal dose–response study indicates:
- The dose where 50% of individuals exhibit the defined effect
- The dose at which the drug is 50% metabolized
- The equilibrium dissociation constant for receptor binding
- The maximal tolerated dose
Correct Answer: The dose where 50% of individuals exhibit the defined effect
Q14. Which statement best describes KD?
- Concentration of drug at which half the receptors are occupied
- Maximal effect achievable by a drug
- Clinical potency in humans
- The slope of the dose–response curve
Correct Answer: Concentration of drug at which half the receptors are occupied
Q15. If two drugs have the same Emax but different EC50, they differ in:
- Efficacy only
- Potency only
- Both potency and efficacy
- Neither potency nor efficacy
Correct Answer: Potency only
Q16. Tachyphylaxis affects the dose–response relationship by:
- Increasing Emax permanently
- Causing a rapid decrease in response to repeated doses
- Mediating only pharmacokinetic tolerance
- Enhancing receptor sensitivity
Correct Answer: Causing a rapid decrease in response to repeated doses
Q17. In a Schild plot, the x‑intercept corresponds to:
- pA2 value indicating antagonist potency
- ED50 of the agonist
- Emax of the antagonist
- Log KD of the agonist
Correct Answer: pA2 value indicating antagonist potency
Q18. What effect does a noncompetitive antagonist have on EC50 and Emax?
- No change in Emax, leftward shift in EC50
- Decrease in Emax; EC50 may be unchanged or appear increased
- Increase in Emax, no change in EC50
- Unpredictable decrease in potency only
Correct Answer: Decrease in Emax; EC50 may be unchanged or appear increased
Q19. Which curve transformation is commonly used to linearize a sigmoidal dose–response for analysis?
- Plotting response vs dose on linear scale
- Log transformation of dose (log‑dose plot)
- Taking the square root of response
- Using reciprocal of response values only
Correct Answer: Log transformation of dose (log‑dose plot)
Q20. An inverse agonist differs from a neutral antagonist because it:
- Blocks receptor without affecting constitutive activity
- Reduces constitutive receptor activity below basal levels
- Has the same effect as a full agonist
- Only acts at nonreceptor targets
Correct Answer: Reduces constitutive receptor activity below basal levels
Q21. In combined drug effects, what describes synergy?
- The combined effect equals the sum of individual effects
- The combined effect is less than the sum of individual effects
- The combined effect is greater than the sum of individual effects
- Two drugs block each other’s effect completely
Correct Answer: The combined effect is greater than the sum of individual effects
Q22. Which factor can shift a dose–response curve rightward, indicating decreased potency?
- Increased receptor expression
- Competitive antagonist present
- Higher intrinsic efficacy of agonist
- Increased drug bioavailability
Correct Answer: Competitive antagonist present
Q23. What is the main difference between pharmacokinetic and pharmacodynamic tolerance?
- Pharmacokinetic tolerance is receptor-based; pharmacodynamic is metabolism-based
- Pharmacokinetic tolerance involves altered drug concentrations; pharmacodynamic involves receptor or post‑receptor changes
- They are identical processes
- Only pharmacodynamic tolerance affects dose–response curves
Correct Answer: Pharmacokinetic tolerance involves altered drug concentrations; pharmacodynamic involves receptor or post‑receptor changes
Q24. The slope of the log-dose response curve is influenced by:
- Only the molecular weight of the drug
- The Hill coefficient and cooperative interactions
- The patient’s age only
- The unit used to express dose
Correct Answer: The Hill coefficient and cooperative interactions
Q25. When calculating margin of safety (MOS), which comparison is typically used?
- ED50 divided by LD50
- LD1 divided by ED99 or similar low‑toxicity/high‑efficacy ratio
- EC50 multiplied by Emax
- KD divided by EC50
Correct Answer: LD1 divided by ED99 or similar low‑toxicity/high‑efficacy ratio
Q26. A drug with a steep dose–response slope implies:
- Small dose changes cause large effect changes
- Dose has no influence on effect
- Large dose changes are needed for effect changes
- Drug is always safe across doses
Correct Answer: Small dose changes cause large effect changes
Q27. In receptor theory, intrinsic activity refers to:
- The ability of an antagonist to block a receptor
- The maximal response a drug can produce relative to a full agonist
- The drug’s absorption rate
- The concentration required for 50% occupancy
Correct Answer: The maximal response a drug can produce relative to a full agonist
Q28. Which experimental measure helps distinguish competitive from noncompetitive antagonism?
- Measuring reflex arcs
- Observing whether Emax can be restored by increasing agonist concentration
- Calculating drug half‑life
- Measuring drug solubility in water
Correct Answer: Observing whether Emax can be restored by increasing agonist concentration
Q29. If a drug’s EC50 is much lower than its KD, what might this indicate?
- Receptor reserve or signal amplification
- Drug has no receptor interactions
- Measurement error only
- Drug is a pure antagonist
Correct Answer: Receptor reserve or signal amplification
Q30. Which concept best explains why two drugs with similar potency may have different clinical effects?
- They must have identical receptor selectivity
- Different efficacy, receptor selectivity, tissue distribution, or intrinsic activity
- Potency fully determines clinical outcome
- Only pharmacokinetics matter, pharmacodynamics is irrelevant
Correct Answer: Different efficacy, receptor selectivity, tissue distribution, or intrinsic activity
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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