Principles of drug action MCQs With Answer

Principles of drug action MCQs With Answer

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Principles of drug action MCQs With Answer introduces B. Pharm students to core concepts in pharmacodynamics and pharmacokinetics, including receptor theory, dose-response relationships, agonists and antagonists, bioavailability, clearance, half-life, and therapeutic index. This concise, keyword-rich overview emphasizes drug–receptor interactions, potency versus efficacy, mechanisms of tolerance and desensitization, ADME (absorption, distribution, metabolism, excretion), enzyme inhibition, and clinical implications for safe dosing. Clear, exam-focused multiple-choice practice strengthens understanding of molecular mechanisms and quantitative calculations essential for rational drug therapy and formulation development. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What best distinguishes pharmacodynamics from pharmacokinetics?

  • Pharmacodynamics studies how the body affects a drug; pharmacokinetics studies the drug’s chemical structure
  • Pharmacodynamics studies drug effects on the body; pharmacokinetics studies the body’s effect on the drug
  • Pharmacodynamics evaluates drug manufacturing; pharmacokinetics evaluates drug marketing
  • Pharmacodynamics measures serum concentrations only; pharmacokinetics measures receptor binding only

Correct Answer: Pharmacodynamics studies drug effects on the body; pharmacokinetics studies the body’s effect on the drug

Q2. In receptor theory, what does ‘affinity’ mean?

  • The ability of a drug to produce a maximal response after binding
  • The rate at which a drug is metabolized by the liver
  • The tendency of a drug to bind to its receptor
  • The capacity of a drug to cross cell membranes

Correct Answer: The tendency of a drug to bind to its receptor

Q3. How is a partial agonist defined?

  • A drug that blocks receptor binding without affecting baseline activity
  • A drug that produces a maximal response greater than a full agonist
  • A drug that produces less than maximal response even at full receptor occupancy
  • A drug that irreversibly activates all receptor subtypes

Correct Answer: A drug that produces less than maximal response even at full receptor occupancy

Q4. What is the typical effect of a competitive antagonist on an agonist dose–response curve?

  • Decrease in Emax with no shift in ED50
  • Rightward shift of the curve with no change in Emax
  • Leftward shift with increased Emax
  • Conversion of agonist into an inverse agonist

Correct Answer: Rightward shift of the curve with no change in Emax

Q5. Noncompetitive antagonists commonly cause which change in a dose–response relationship?

  • Parallel rightward shift without Emax change
  • Increase in potency with no efficacy change
  • Decrease in maximal effect (Emax) regardless of agonist concentration
  • Enhanced receptor affinity for the agonist

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

Q6. Which statement correctly differentiates potency and efficacy?

  • Potency is the maximum effect a drug can produce; efficacy is the dose required for effect
  • Potency is a safety margin; efficacy is the bioavailability
  • Potency refers to the dose needed to achieve an effect; efficacy refers to the maximum effect achievable
  • Potency and efficacy are interchangeable pharmacokinetic terms

Correct Answer: Potency refers to the dose needed to achieve an effect; efficacy refers to the maximum effect achievable

Q7. What does ED50 represent in pharmacology?

  • The dose that is lethal to 50% of the population
  • The dose that produces 50% of the maximal effect
  • The dose absorbed unchanged into systemic circulation
  • The concentration at which 50% of receptors are degraded

Correct Answer: The dose that produces 50% of the maximal effect

Q8. How is the therapeutic index (TI) usually calculated?

  • TI = ED50 / LD50
  • TI = LD50 / ED50
  • TI = Cmax / Tmax
  • TI = Vd / Cl

Correct Answer: TI = LD50 / ED50

Q9. What is ‘bioavailability’ (F)?

  • The fraction of administered drug that reaches systemic circulation unchanged
  • The percentage of drug excreted unchanged in urine
  • The drug’s ability to bind to the target receptor
  • The time taken to reach peak concentration

Correct Answer: The fraction of administered drug that reaches systemic circulation unchanged

Q10. Which process primarily causes low oral bioavailability for some drugs?

  • First-pass metabolism in the liver and gut wall
  • Complete passive diffusion across intestinal epithelium
  • High glomerular filtration rate
  • Complete stability in the gastrointestinal tract

Correct Answer: First-pass metabolism in the liver and gut wall

Q11. What is the pharmacokinetic definition of half-life (t1/2)?

  • The time for the body to absorb 50% of an oral dose
  • The time for the plasma concentration to decrease by half
  • The time to reach peak plasma concentration after dosing
  • The time for 50% of receptors to be occupied

Correct Answer: The time for the plasma concentration to decrease by half

Q12. Clearance (Cl) is best described as:

  • The rate of drug metabolism in mg/min only
  • The volume of plasma completely cleared of drug per unit time
  • The total amount of drug eliminated per dose
  • The fraction of drug bound to plasma proteins

Correct Answer: The volume of plasma completely cleared of drug per unit time

Q13. What does a large volume of distribution (Vd) indicate?

  • Drug is largely confined to plasma
  • Drug extensively distributes into tissues outside plasma
  • Drug has poor membrane permeability
  • Drug is not protein bound

Correct Answer: Drug extensively distributes into tissues outside plasma

Q14. Approximately how many half-lives are required to reach steady state during continuous dosing?

  • About 1 half-life
  • About 2 half-lives
  • About 4–5 half-lives
  • About 10–12 half-lives

Correct Answer: About 4–5 half-lives

Q15. Which statement correctly contrasts zero-order and first-order kinetics?

  • Zero-order elimination: constant fraction removed per unit time; First-order: constant amount removed
  • Zero-order elimination: constant amount removed per unit time; First-order: constant fraction removed per unit time
  • Both zero- and first-order always have linear elimination with dose
  • First-order occurs only for drugs with saturable enzymes

Correct Answer: Zero-order elimination: constant amount removed per unit time; First-order: constant fraction removed per unit time

Q16. What is a ‘prodrug’?

  • A drug that is toxic until detoxified
  • A compound administered in inactive form that is metabolized to an active drug
  • An antagonist that converts to an agonist in vivo
  • A drug that cannot cross cell membranes

Correct Answer: A compound administered in inactive form that is metabolized to an active drug

Q17. Which property makes a competitive antagonist ‘surmountable’ by increasing agonist concentration?

  • Irreversible covalent binding to the receptor
  • Binding to an allosteric site causing receptor internalization
  • Reversible binding at the agonist’s active site
  • Induction of metabolic enzymes that degrade the agonist

Correct Answer: Reversible binding at the agonist’s active site

Q18. What is the functional consequence of ‘spare receptors’?

  • Maximal response requires occupancy of all receptors
  • Maximal response can occur without full receptor occupancy
  • Receptors are resistant to antagonists because they are intracellular
  • Spare receptors are permanently inactive

Correct Answer: Maximal response can occur without full receptor occupancy

Q19. An inverse agonist differs from a neutral antagonist because it:

  • Blocks the receptor but has no effect on constitutive activity
  • Increases receptor constitutive activity above baseline
  • Reduces constitutive receptor activity below basal levels
  • Only binds irreversibly to receptors

Correct Answer: Reduces constitutive receptor activity below basal levels

Q20. Allosteric modulators act by:

  • Binding to the same active site as the endogenous ligand
  • Modifying receptor response by binding to a distinct site from the agonist
  • Increasing drug renal clearance universally
  • Preventing drug absorption in the GI tract

Correct Answer: Modifying receptor response by binding to a distinct site from the agonist

Q21. ‘Tachyphylaxis’ is best described as:

  • Slowly developing tolerance over months of therapy
  • Rapid decrease in response after repeated dosing over a short period
  • An increase in drug potency with repeated use
  • Permanent loss of receptor proteins following a single dose

Correct Answer: Rapid decrease in response after repeated dosing over a short period

Q22. Which cellular process commonly causes receptor desensitization after prolonged agonist exposure?

  • Phosphorylation and receptor internalization
  • Increased DNA transcription of receptor genes
  • Enhanced translation of receptor proteins
  • Immediate increase in receptor synthesis

Correct Answer: Phosphorylation and receptor internalization

Q23. A Hill coefficient (nH) greater than 1 indicates:

  • No binding between ligand and receptor
  • Negative cooperativity among binding sites
  • Positive cooperativity among binding sites
  • That the drug is an irreversible antagonist

Correct Answer: Positive cooperativity among binding sites

Q24. In enzyme kinetics, a competitive inhibitor typically affects Vmax and Km how?

  • Vmax decreases; Km unchanged
  • Vmax unchanged; apparent Km increases
  • Both Vmax and Km decrease proportionally
  • Vmax increases; Km decreases

Correct Answer: Vmax unchanged; apparent Km increases

Q25. An irreversible antagonist usually reduces drug response by:

  • Reversibly occupying the agonist binding site
  • Forming a covalent bond that permanently inactivates receptors
  • Increasing agonist synthesis to outcompete binding
  • Blocking renal excretion of the agonist

Correct Answer: Forming a covalent bond that permanently inactivates receptors

Q26. Intestinal P-glycoprotein (P-gp) primarily affects oral drugs by:

  • Increasing passive diffusion into enterocytes
  • Pumping drugs back into the intestinal lumen, reducing absorption
  • Converting drugs into prodrugs in the gut lumen
  • Neutralizing acidic drugs in the stomach

Correct Answer: Pumping drugs back into the intestinal lumen, reducing absorption

Q27. The relationship between half-life, volume of distribution (Vd), and clearance (Cl) is given by which equation?

  • t1/2 = 0.693 × Cl / Vd
  • t1/2 = 0.693 × Vd / Cl
  • t1/2 = Vd × Cl
  • t1/2 = Cl / (0.693 × Vd)

Correct Answer: t1/2 = 0.693 × Vd / Cl

Q28. Induction of hepatic CYP450 enzymes by one drug will most likely:

  • Decrease the clearance of other drugs metabolized by those enzymes
  • Increase plasma levels and toxicity of co-administered substrates
  • Increase clearance and reduce plasma levels of co-administered substrates
  • Always cause renal failure

Correct Answer: Increase clearance and reduce plasma levels of co-administered substrates

Q29. The ‘therapeutic window’ refers to:

  • The dose range between the ED1 and ED99 values only
  • The concentration range between minimum effective concentration and minimum toxic concentration
  • The time period during which a drug is marketed
  • The range of half-lives observed in a population

Correct Answer: The concentration range between minimum effective concentration and minimum toxic concentration

Q30. Which statement about insurmountable antagonism is correct?

  • It can always be overcome by increasing agonist concentration
  • It reduces potency but never affects efficacy
  • It cannot be fully overcome by adding more agonist and often reduces Emax
  • It only occurs with reversible competitive antagonists

Correct Answer: It cannot be fully overcome by adding more agonist and often reduces Emax

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