Agonists MCQs With Answer

Agonists MCQs With Answer

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Introduction: Agonists MCQs With Answer is a focused study tool for B. Pharm students to master pharmacodynamics, drug‑receptor interactions, and therapeutic applications of agonists. This concise, keyword‑rich introduction covers concepts like full agonist, partial agonist, inverse agonist, biased agonism, affinity, efficacy, potency, EC50, Kd, spare receptors, desensitization, and allosteric modulation. Understanding these mechanisms helps in predicting drug responses, adverse effects, and clinical use of adrenergic, muscarinic, opioid and other receptor agonists. These MCQs emphasize mechanism, examples, dose‑response relationships, and clinical relevance to deepen learning and exam preparation.
Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary action of a pharmacologic agonist at a receptor?

  • Blocks the receptor and prevents signaling
  • Binds the receptor and stabilizes its inactive form
  • Binds the receptor and produces a cellular response
  • Promotes receptor degradation without signaling

Correct Answer: Binds the receptor and produces a cellular response

Q2. How does a partial agonist differ from a full agonist?

  • Partial agonist has higher affinity but no efficacy
  • Partial agonist produces lower maximal response even at full receptor occupancy
  • Partial agonist binds an allosteric site only
  • Partial agonist always acts as an inverse agonist in vivo

Correct Answer: Partial agonist produces lower maximal response even at full receptor occupancy

Q3. What defines an inverse agonist?

  • It produces the same effect as the agonist at higher potency
  • It increases constitutive receptor activity
  • It reduces constitutive receptor activity, producing opposite effect to agonist
  • It only binds to receptor when agonist is absent

Correct Answer: It reduces constitutive receptor activity, producing opposite effect to agonist

Q4. Which parameter describes drug potency?

  • Maximum effect (Emax)
  • EC50, the concentration producing 50% of Emax
  • Intrinsic activity at receptor
  • Number of receptors in tissue

Correct Answer: EC50, the concentration producing 50% of Emax

Q5. What does a lower Kd value indicate about a drug‑receptor interaction?

  • Lower affinity of drug for receptor
  • Higher affinity of drug for receptor
  • Faster receptor desensitization
  • Greater intrinsic efficacy

Correct Answer: Higher affinity of drug for receptor

Q6. What is meant by “spare receptors” in pharmacology?

  • Extra receptors that do not bind drug due to mutation
  • Receptors that are permanently inactive
  • A receptor population in excess so maximal response occurs without full occupancy
  • Receptors located in intracellular compartments only

Correct Answer: A receptor population in excess so maximal response occurs without full occupancy

Q7. How does a competitive antagonist affect an agonist dose‑response curve?

  • Decreases Emax without changing potency
  • Shifts the curve to the right (decreased potency) without altering Emax if reversible
  • Converts agonist to inverse agonist
  • Increases efficacy of the agonist

Correct Answer: Shifts the curve to the right (decreased potency) without altering Emax if reversible

Q8. What is the typical effect of a noncompetitive antagonist?

  • Only alters agonist potency, not efficacy
  • Reduces maximal effect (Emax) regardless of agonist concentration
  • Acts only at low agonist concentrations
  • Is always reversible by increasing agonist concentration

Correct Answer: Reduces maximal effect (Emax) regardless of agonist concentration

Q9. Which statement best describes a drug with biased agonism?

  • Activates all downstream pathways equally after receptor binding
  • Preferentially activates specific signaling pathways over others via the same receptor
  • Only binds to mutated receptors in diseased tissues
  • Acts as an agonist in one organ and antagonist in another due to metabolism

Correct Answer: Preferentially activates specific signaling pathways over others via the same receptor

Q10. Why can a partial agonist behave as an antagonist in presence of a full agonist?

  • Because it reduces receptor number
  • Because it competes for binding but produces a lower response, lowering overall effect
  • Because it converts the full agonist to an antagonist chemically
  • Because partial agonists only bind allosteric sites

Correct Answer: Because it competes for binding but produces a lower response, lowering overall effect

Q11. Which example is a classic beta‑2 adrenergic agonist used in asthma?

  • Propranolol
  • Salbutamol (albuterol)
  • Metoprolol
  • Phenoxybenzamine

Correct Answer: Salbutamol (albuterol)

Q12. Which drug is an example of a muscarinic receptor agonist used to stimulate bladder contraction?

  • Atropine
  • Bethanechol
  • Scopolamine
  • Glycopyrrolate

Correct Answer: Bethanechol

Q13. Which opioid is a well‑known full agonist at mu opioid receptors?

  • Buprenorphine
  • Morphine
  • Naloxone
  • Pentazocine

Correct Answer: Morphine

Q14. Which opioid acts as a partial agonist and is used for opioid dependence with a ceiling effect on respiratory depression?

  • Fentanyl
  • Buprenorphine
  • Codeine
  • Methadone

Correct Answer: Buprenorphine

Q15. Many H1 antihistamines act as which of the following at the histamine H1 receptor?

  • Full agonists
  • Partial agonists
  • Inverse agonists
  • Irreversible antagonists only

Correct Answer: Inverse agonists

Q16. Benzodiazepines enhance GABAergic signaling by which mechanism?

  • Direct agonism at the GABA binding site
  • Positive allosteric modulation of GABA-A receptors
  • Blocking GABA reuptake transporters
  • Irreversible activation of GABA receptors

Correct Answer: Positive allosteric modulation of GABA-A receptors

Q17. What is receptor desensitization?

  • Permanent increase in receptor gene copy number
  • Short‑term loss of receptor responsiveness after prolonged agonist exposure
  • Immediate increase in agonist potency
  • Creation of new receptor subtypes

Correct Answer: Short‑term loss of receptor responsiveness after prolonged agonist exposure

Q18. Chronic exposure to an agonist commonly causes which cellular adaptation?

  • Up‑regulation of receptor number
  • Down‑regulation or internalization of receptors
  • Conversion of agonist to antagonist
  • Increase in agonist intrinsic efficacy

Correct Answer: Down‑regulation or internalization of receptors

Q19. Which measurement is used to quantify antagonist potency in Schild analysis?

  • pKa value
  • pA2 value
  • Therapeutic index
  • Bioavailability percentage

Correct Answer: pA2 value

Q20. Phenylephrine is primarily used therapeutically because it is an agonist at which receptor subtype?

  • Beta‑2 adrenergic receptor
  • Alpha‑1 adrenergic receptor
  • Muscarinic M2 receptor
  • Opioid mu receptor

Correct Answer: Alpha‑1 adrenergic receptor

Q21. Which beta‑blocker has partial agonist (intrinsic sympathomimetic) activity?

  • Propranolol
  • Pindolol
  • Metoprolol
  • Atenolol

Correct Answer: Pindolol

Q22. What is Emax in a dose‑response relationship?

  • The concentration that kills 50% of cells
  • The maximal effect a drug can produce in a given system
  • The affinity constant of the drug for the receptor
  • The baseline response in absence of drug

Correct Answer: The maximal effect a drug can produce in a given system

Q23. How do spare receptors affect apparent drug potency?

  • They decrease potency by requiring full occupancy
  • They increase apparent potency because full effect occurs at lower occupancy
  • They convert partial agonists into inverse agonists
  • They eliminate all antagonist effects

Correct Answer: They increase apparent potency because full effect occurs at lower occupancy

Q24. Pentazocine is classified as which type of opioid receptor ligand?

  • Pure mu full agonist
  • Kappa agonist and mu partial agonist/antagonist (mixed agonist‑antagonist)
  • Inverse agonist at all opioid receptors
  • Selective delta receptor antagonist only

Correct Answer: Kappa agonist and mu partial agonist/antagonist (mixed agonist‑antagonist)

Q25. A positive allosteric modulator (PAM) typically does which of the following?

  • Binds to the orthosteric site and activates receptor alone
  • Enhances the effect of the endogenous agonist at a separate site
  • Blocks the receptor irreversibly
  • Converts a full agonist into a partial agonist

Correct Answer: Enhances the effect of the endogenous agonist at a separate site

Q26. Which clinical feature is commonly associated with tolerance to an agonist?

  • Increased sensitivity to the drug after repeated use
  • Requirement of higher dose to achieve same response
  • Immediate severe allergic reaction on repeated dosing
  • Permanent increase in drug half‑life

Correct Answer: Requirement of higher dose to achieve same response

Q27. Which adverse effect is reduced by using a partial agonist instead of a full agonist?

  • Complete loss of therapeutic effect
  • Absolute prevention of tolerance
  • Lower maximal adverse events due to ceiling effect (e.g., respiratory depression)
  • Increased irreversible receptor down‑regulation

Correct Answer: Lower maximal adverse events due to ceiling effect (e.g., respiratory depression)

Q28. A left shift of a drug’s dose‑response curve indicates which change?

  • Decreased potency
  • Increased potency
  • Decreased efficacy
  • Complete antagonism

Correct Answer: Increased potency

Q29. Which mechanism best explains pharmacodynamic tolerance to an agonist?

  • Enzyme induction increasing drug metabolism only
  • Receptor phosphorylation, uncoupling, or down‑regulation reducing response
  • Immediate immune destruction of drug molecules
  • Increase in drug bioavailability over time

Correct Answer: Receptor phosphorylation, uncoupling, or down‑regulation reducing response

Q30. For exam preparation, which concept links affinity, efficacy, and clinical response of agonists?

  • Pharmacokinetics only
  • Drug‑receptor theory and dose‑response relationships
  • Renal clearance mechanisms only
  • First‑pass metabolism exclusively

Correct Answer: Drug‑receptor theory and dose‑response relationships

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