Drug tolerance MCQs With Answer — For B.Pharm students: Drug tolerance is a progressive reduction in drug effect after repeated exposure, involving pharmacokinetic and pharmacodynamic mechanisms, receptor desensitization, enzyme induction, and behavioral adaptation. This introduction covers key concepts such as tachyphylaxis, cross-tolerance, dose–response curve shifts, clinical examples (opioids, benzodiazepines, nitrates), and management strategies like drug holidays and dose adjustment. Understanding molecular mechanisms, therapeutic implications, and measurement methods is essential for safe pharmacotherapy and rational dosing. These focused, exam-oriented MCQs reinforce mechanisms, examples, and clinical decision-making relevant to undergraduate pharmacy practice. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the best definition of drug tolerance?
- A progressive increase in adverse effects with repeated dosing
- A decrease in response to a drug after repeated administration
- An immediate allergic reaction to a drug
- Permanent loss of drug effect after a single dose
Correct Answer: A decrease in response to a drug after repeated administration
Q2. Which statement best distinguishes pharmacokinetic from pharmacodynamic tolerance?
- Pharmacokinetic tolerance involves receptor down-regulation; pharmacodynamic involves increased drug metabolism
- Pharmacokinetic tolerance results from increased drug metabolism or clearance; pharmacodynamic tolerance results from receptor-level adaptations
- Both types are only behavioral phenomena
- Pharmacodynamic tolerance always increases drug absorption
Correct Answer: Pharmacokinetic tolerance results from increased drug metabolism or clearance; pharmacodynamic tolerance results from receptor-level adaptations
Q3. Tachyphylaxis is best described as:
- A slow, weeks-long development of tolerance
- A rapid decrease in drug response after repeated dosing over minutes to hours
- Complete cross-tolerance between unrelated drugs
- A permanent genetic change caused by drug exposure
Correct Answer: A rapid decrease in drug response after repeated dosing over minutes to hours
Q4. Cross-tolerance refers to:
- Tolerance to drug A leading to increased sensitivity to drug B
- Tolerance to drug A reducing response to drug B with similar mechanisms
- The development of antibodies that neutralize multiple drugs
- Tolerance that only occurs with combination therapy
Correct Answer: Tolerance to drug A reducing response to drug B with similar mechanisms
Q5. Receptor down-regulation as a mechanism of tolerance typically causes which change in a dose–response curve?
- Leftward shift with increased Emax
- Rightward shift with unchanged Emax
- Decrease in maximum effect (reduced Emax)
- No change in potency or efficacy
Correct Answer: Decrease in maximum effect (reduced Emax)
Q6. Which of the following is a classic example of pharmacokinetic tolerance?
- GABA-A receptor internalization after chronic benzodiazepine use
- Induction of hepatic CYP enzymes by rifampicin reducing drug levels
- Receptor phosphorylation causing desensitization
- Immediate neurotransmitter depletion
Correct Answer: Induction of hepatic CYP enzymes by rifampicin reducing drug levels
Q7. Which cellular process commonly underlies rapid receptor desensitization?
- Increased gene transcription of the receptor
- Phosphorylation and internalization of receptors
- Permanent mutation of receptor DNA
- Enhanced membrane synthesis
Correct Answer: Phosphorylation and internalization of receptors
Q8. A rightward shift of a dose–response curve with unchanged Emax most likely indicates:
- Increased drug potency
- Pharmacokinetic tolerance or competitive antagonism
- Reduced maximum achievable effect due to receptor loss
- Irreversible receptor blockade
Correct Answer: Pharmacokinetic tolerance or competitive antagonism
Q9. Which pharmacodynamic change would most likely reduce Emax rather than shift EC50?
- Increased drug clearance by the liver
- Competitive antagonism at the receptor
- Loss of receptor number (down-regulation)
- Decreased drug absorption from the gut
Correct Answer: Loss of receptor number (down-regulation)
Q10. In opioid therapy, tolerance most commonly develops to which effects?
- Constipation and miosis
- Analgesia and respiratory depression
- Allergic reactions
- Renal clearance of opioids
Correct Answer: Analgesia and respiratory depression
Q11. Which clinical strategy can reduce development of tolerance to a chronically used drug?
- Continuous high-dose infusion without breaks
- Frequent dose escalation at short intervals
- Drug holidays or intermittent dosing
- Combining with pharmacokinetic inducers
Correct Answer: Drug holidays or intermittent dosing
Q12. Nitroglycerin tolerance during continuous therapy is an example of:
- Immunologic tolerance
- Tachyphylaxis and tolerance due to neurohormonal counter-regulation
- Genetic polymorphism
- Primary resistance caused by receptor mutation
Correct Answer: Tachyphylaxis and tolerance due to neurohormonal counter-regulation
Q13. Cross-tolerance between ethanol and benzodiazepines is largely due to:
- Shared effects on the GABA-A receptor complex
- Both drugs inducing the same CYP enzymes
- Identical chemical structure
- Similar renal excretion pathways
Correct Answer: Shared effects on the GABA-A receptor complex
Q14. Sensitization or reverse tolerance refers to:
- Progressive loss of drug effect over time
- An increased response to a drug after repeated exposure
- An allergic sensitization unrelated to dose
- Tolerance transferable across drug classes
Correct Answer: An increased response to a drug after repeated exposure
Q15. Which lab or clinical measure would you use to detect pharmacokinetic tolerance?
- Decreased plasma drug concentration at steady state despite same dose
- Reduced receptor expression on biopsy
- Measurement of withdrawal symptoms only
- Genotyping of receptor variants
Correct Answer: Decreased plasma drug concentration at steady state despite same dose
Q16. Chronic administration of a beta-2 agonist leading to decreased bronchodilator response is due to:
- Formation of antibodies against the drug
- Receptor desensitization and down-regulation
- Enhanced drug absorption from the lung
- Improved airway remodeling
Correct Answer: Receptor desensitization and down-regulation
Q17. Which of the following best differentiates tolerance from physiological dependence?
- Tolerance causes withdrawal symptoms; dependence does not
- Dependence is the need to continue drug to prevent withdrawal; tolerance is reduced effect at a given dose
- Tolerance is immunologic; dependence is metabolic
- They are identical phenomena with different names
Correct Answer: Dependence is the need to continue drug to prevent withdrawal; tolerance is reduced effect at a given dose
Q18. Chronic enzyme induction by a drug would most likely cause which clinical outcome for a co-administered substrate drug?
- Increased plasma levels and toxicity
- Decreased plasma levels and reduced efficacy
- No change in drug levels
- Immediate allergic reaction
Correct Answer: Decreased plasma levels and reduced efficacy
Q19. Which agent is less likely to produce progressive tolerance due to its partial agonist profile?
- Morphine (full opioid agonist)
- Buprenorphine (partial opioid agonist)
- Methadone (full opioid agonist)
- Fentanyl (full opioid agonist)
Correct Answer: Buprenorphine (partial opioid agonist)
Q20. Tachyphylaxis to topical decongestants (e.g., oxymetazoline) is mainly due to:
- Systemic enzyme induction
- Local receptor desensitization and reduced responsiveness
- Increased drug absorption causing toxicity
- Autoimmune destruction of receptors
Correct Answer: Local receptor desensitization and reduced responsiveness
Q21. Which experimental finding indicates pharmacodynamic tolerance rather than pharmacokinetic?
- Reduced plasma concentration of the drug after repeated dosing
- Restored plasma concentration but reduced tissue response to the same concentration
- Increased urinary excretion of the parent drug
- Shortened half-life due to enzyme induction
Correct Answer: Restored plasma concentration but reduced tissue response to the same concentration
Q22. Long-term benzodiazepine use can lead to tolerance primarily by:
- Increasing GABA synthesis indefinitely
- Alterations in GABA-A receptor subunit composition and function
- Enhancing gastrointestinal absorption of benzodiazepines
- Permanent elimination of benzodiazepine binding sites
Correct Answer: Alterations in GABA-A receptor subunit composition and function
Q23. Which intervention is most appropriate when tolerance causes loss of efficacy for a critical analgesic in a chronic pain patient?
- Abruptly stop the analgesic without plan
- Assess for tolerance mechanisms and consider opioid rotation or multimodal analgesia
- Double the dose every day until pain resolves
- Switch to an unrelated antibiotic
Correct Answer: Assess for tolerance mechanisms and consider opioid rotation or multimodal analgesia
Q24. Which of the following illustrates cross-tolerance within the same drug class?
- Tolerance to morphine causing reduced response to heroin
- Tolerance to aspirin causing reduced response to acetaminophen
- Tolerance to a beta-blocker improving response to a calcium channel blocker
- Tolerance to insulin increasing sensitivity to glucagon
Correct Answer: Tolerance to morphine causing reduced response to heroin
Q25. A patient on chronic stimulant therapy experiences reduced response over months. Which mechanism is least likely?
- Receptor down-regulation
- Neurotransmitter depletion
- Hepatic enzyme induction increasing clearance
- Increased gut absorption of the stimulant
Correct Answer: Increased gut absorption of the stimulant
Q26. Which statement about tolerance reversibility is most accurate?
- Tolerance is always permanent and irreversible
- Some forms of tolerance (e.g., receptor regulation) can be partly reversible after drug cessation
- Tolerance reverses within seconds of stopping the drug
- Tolerance can be reversed only by increasing the dose indefinitely
Correct Answer: Some forms of tolerance (e.g., receptor regulation) can be partly reversible after drug cessation
Q27. If chronic drug exposure increases EC50 without changing Emax, this suggests:
- Pharmacokinetic tolerance or competitive antagonism
- Loss of receptor number
- Irreversible receptor blockade
- Increased intrinsic efficacy of the agonist
Correct Answer: Pharmacokinetic tolerance or competitive antagonism
Q28. Which clinical example demonstrates tachyphylaxis observed within a short timeframe?
- Loss of antihypertensive effect after years of use
- Rapid loss of nasal decongestant effect after repeated intranasal doses
- Development of antibiotic resistance after a single dose
- Slow tolerance to levodopa over decades
Correct Answer: Rapid loss of nasal decongestant effect after repeated intranasal doses
Q29. Which factor can predispose a patient to faster development of pharmacokinetic tolerance?
- Concurrent use of enzyme inhibitors
- Genetic polymorphism causing poor metabolizer phenotype
- Use of enzyme inducers like carbamazepine or rifampicin
- Administration by intravenous bolus only once
Correct Answer: Use of enzyme inducers like carbamazepine or rifampicin
Q30. Why is understanding tolerance important for B.Pharm students in clinical practice?
- It has no impact on dosing or patient safety
- It guides dose adjustments, monitoring, prevention of withdrawal, and safer prescribing
- It only matters for veterinary pharmacology
- It replaces the need to know pharmacokinetics
Correct Answer: It guides dose adjustments, monitoring, prevention of withdrawal, and safer prescribing
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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