Drug–receptor interactions MCQs With Answer

Drug–receptor interactions MCQs With Answer

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Understanding drug–receptor interactions is central to pharmacodynamics and essential for B. Pharm students preparing for therapeutics and research. This concise guide reviews how drugs bind receptors, definitions of affinity and efficacy, distinctions between agonists, partial agonists, antagonists, inverse agonists, and mechanisms of competitive and noncompetitive inhibition. Key concepts include dose–response curves, EC50 and Kd, receptor reserve (spare receptors), allosteric modulation, desensitization, and signal transduction pathways (GPCRs, ion channels, enzyme-linked receptors). It also links molecular mechanisms to clinical outcomes and laboratory assays used in pharmacology. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What does the term “affinity” describe in drug–receptor interactions?

  • The maximum response produced by a drug
  • The drug concentration producing 50% of maximal effect
  • The strength of binding between a drug and its receptor
  • The speed at which a drug is metabolized

Correct Answer: The strength of binding between a drug and its receptor

Q2. Which parameter is used to quantify potency in a dose–response curve?

  • Intrinsic activity
  • EC50
  • Emax
  • Kd

Correct Answer: EC50

Q3. Efficacy of a drug refers to:

  • The concentration required to occupy 50% of receptors
  • The maximum effect a drug can produce regardless of dose
  • The ability of a drug to cross membranes
  • The duration of action of a drug

Correct Answer: The maximum effect a drug can produce regardless of dose

Q4. A competitive antagonist typically:

  • Reduces Emax without shifting the dose–response curve
  • Shifts the dose–response curve to the right without reducing Emax
  • Irreversibly inactivates receptors
  • Enhances intrinsic activity of agonists

Correct Answer: Shifts the dose–response curve to the right without reducing Emax

Q5. Which concept explains why a full response can be obtained without all receptors being occupied?

  • Allosteric modulation
  • Receptor reserve (spare receptors)
  • Inverse agonism
  • Competitive antagonism

Correct Answer: Receptor reserve (spare receptors)

Q6. Kd is best defined as:

  • The drug concentration producing half-maximal effect
  • The equilibrium dissociation constant representing affinity
  • The maximal binding capacity of tissue
  • The rate of receptor internalization

Correct Answer: The equilibrium dissociation constant representing affinity

Q7. A partial agonist at a receptor will:

  • Produce no response but block agonists
  • Produce a submaximal response even at full receptor occupancy
  • Always act as a noncompetitive antagonist
  • Increase receptor expression

Correct Answer: Produce a submaximal response even at full receptor occupancy

Q8. Which statement about inverse agonists is correct?

  • They increase constitutive receptor activity
  • They stabilize receptors in an inactive conformation, reducing basal activity
  • They have higher efficacy than full agonists
  • They are identical to competitive antagonists in all systems

Correct Answer: They stabilize receptors in an inactive conformation, reducing basal activity

Q9. Noncompetitive antagonists usually:

  • Compete with agonists at the same binding site
  • Decrease Emax irrespective of agonist concentration
  • Only shift the dose–response curve to the right
  • Act by increasing receptor synthesis

Correct Answer: Decrease Emax irrespective of agonist concentration

Q10. In the context of receptor theory, intrinsic activity refers to:

  • The ability of a drug to bind to plasma proteins
  • The efficacy of a drug in activating a receptor once bound
  • The drug’s lipophilicity
  • The receptor’s genetic polymorphism

Correct Answer: The efficacy of a drug in activating a receptor once bound

Q11. Schild analysis is primarily used to:

  • Determine the Emax of an agonist
  • Quantify the potency of a competitive antagonist (pA2)
  • Measure receptor internalization rates
  • Estimate intrinsic activity of partial agonists

Correct Answer: Quantify the potency of a competitive antagonist (pA2)

Q12. Tachyphylaxis refers to:

  • A gradual increase in drug sensitivity over weeks
  • An acute, rapidly developing decrease in response to repeated drug doses
  • Permanent receptor deletion after one dose
  • Enhanced drug absorption after repeated dosing

Correct Answer: An acute, rapidly developing decrease in response to repeated drug doses

Q13. Allosteric modulators:

  • Bind to the same site as the endogenous ligand
  • Can modify receptor response by binding to a different site
  • Always act as antagonists
  • Irreversibly block receptors

Correct Answer: Can modify receptor response by binding to a different site

Q14. Which receptor family commonly signals via G proteins and second messengers?

  • Ligand-gated ion channels
  • G protein-coupled receptors (GPCRs)
  • Receptor tyrosine kinases
  • Nuclear hormone receptors

Correct Answer: G protein-coupled receptors (GPCRs)

Q15. The Scatchard plot is used to analyze:

  • Clinical trial outcomes
  • Receptor binding data to derive Bmax and Kd
  • Dose–response curves for efficacy
  • Pharmacokinetic half-life

Correct Answer: Receptor binding data to derive Bmax and Kd

Q16. A drug with high affinity and low intrinsic activity is most likely a:

  • Full agonist
  • Partial agonist
  • Competitive antagonist
  • Inverse agonist

Correct Answer: Partial agonist

Q17. Physiological antagonism describes:

  • Two drugs acting at the same receptor site
  • Opposing physiological effects produced via different receptors or pathways
  • Irreversible blocking of receptors by a toxin
  • Synergistic increase of drug effect

Correct Answer: Opposing physiological effects produced via different receptors or pathways

Q18. Which term best describes a drug that increases the effect of an agonist when co-administered but has little activity alone?

  • Full agonist
  • Positive allosteric modulator
  • Inverse agonist
  • Noncompetitive antagonist

Correct Answer: Positive allosteric modulator

Q19. Receptor up-regulation typically occurs in response to:

  • Chronic agonist exposure
  • Chronic antagonist exposure
  • Acute agonist overdose
  • Single low-dose administration

Correct Answer: Chronic antagonist exposure

Q20. Which method directly measures drug–receptor binding affinity in vitro?

  • Western blotting of receptor protein
  • Radioligand binding assay
  • ELISA for cytokines
  • Mass spectrometry of metabolites

Correct Answer: Radioligand binding assay

Q21. “Spare receptors” increase:

  • Apparent potency of agonists by allowing maximal response at lower occupancy
  • Rate of drug metabolism
  • Drug clearance from plasma
  • Degree of irreversible antagonism

Correct Answer: Apparent potency of agonists by allowing maximal response at lower occupancy

Q22. An irreversible antagonist usually produces its effect by:

  • Reversibly blocking the orthosteric site
  • Covalently modifying the receptor, decreasing Emax
  • Increasing receptor synthesis
  • Competing with agonist for transient binding

Correct Answer: Covalently modifying the receptor, decreasing Emax

Q23. The two-state model of receptor activation proposes:

  • Receptors exist only in one active conformation
  • Receptors interconvert between active and inactive states, influenced by ligands
  • All drugs act as full agonists
  • Affinity and efficacy are identical properties

Correct Answer: Receptors interconvert between active and inactive states, influenced by ligands

Q24. Which factor does NOT directly affect drug–receptor binding in vivo?

  • Plasma protein binding of the drug
  • Local pH at the receptor site
  • Genetic polymorphism of the receptor
  • Color of the tablet formulation

Correct Answer: Color of the tablet formulation

Q25. A shift of a dose–response curve to the left indicates:

  • Decreased potency
  • Increased potency
  • Decreased efficacy
  • Irreversible antagonism

Correct Answer: Increased potency

Q26. Receptor desensitization can result from:

  • Prolonged agonist exposure causing phosphorylation and internalization
  • Acute antagonist exposure increasing receptor numbers
  • Reduced drug distribution to tissues
  • Enhanced renal clearance only

Correct Answer: Prolonged agonist exposure causing phosphorylation and internalization

Q27. Selectivity of a drug means:

  • The drug produces a single effect in all tissues
  • The drug preferentially binds certain receptor subtypes over others
  • The drug has equal affinity for all receptors
  • The drug cannot be metabolized

Correct Answer: The drug preferentially binds certain receptor subtypes over others

Q28. Which is an example of a second messenger commonly activated by GPCRs?

  • DNA
  • cAMP
  • Hemoglobin
  • Albumin

Correct Answer: cAMP

Q29. A drug that reduces basal signaling of a constitutively active receptor will be classified as:

  • Neutral antagonist
  • Inverse agonist
  • Partial agonist
  • Allosteric enhancer

Correct Answer: Inverse agonist

Q30. Why is understanding receptor polymorphism important in B. Pharm practice?

  • It dictates the physical appearance of tablets
  • It helps predict interindividual variability in drug response and adverse effects
  • It determines packaging requirements
  • It only affects IV infusion rates

Correct Answer: It helps predict interindividual variability in drug response and adverse effects

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