Idiosyncrasy MCQs With Answer

Idiosyncrasy MCQs With Answer

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Introduction: Understanding idiosyncratic drug reactions is essential for B.Pharm students preparing for clinical pharmacy and pharmacology roles. This set of Idiosyncrasy MCQs With Answer focuses on mechanisms, risk factors, pharmacogenetics, immune-mediated and metabolic idiosyncrasies, HLA associations, CYP450 polymorphisms, clinical presentation, diagnosis, prevention and management. Each question emphasizes concepts like non-dose-dependent adverse drug reactions, biomarkers, drug monitoring, and individualized therapy to build competence in ADR recognition and safe prescribing. These targeted multiple-choice questions will reinforce critical thinking about molecular mechanisms, patient susceptibility, and therapeutic decision-making in real-world scenarios. Answers include brief explanations and references to pharmacovigilance principles to aid revision. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What defines an idiosyncratic drug reaction?

  • A predictable, dose-dependent extension of a drug’s pharmacologic effect
  • An unpredictable, non–dose-dependent adverse effect often related to individual susceptibility
  • A mild, common side effect seen in most patients
  • An adverse effect prevented by increasing the dose slowly

Correct Answer: An unpredictable, non–dose-dependent adverse effect often related to individual susceptibility

Q2. Which of the following best characterizes immune-mediated idiosyncratic reactions?

  • Immediate dose-related toxicity due to overdose
  • Involves specific HLA alleles or drug-specific T-cell responses
  • Always occurs within minutes of first exposure
  • Caused exclusively by renal impairment

Correct Answer: Involves specific HLA alleles or drug-specific T-cell responses

Q3. Which example is a classic immune-mediated idiosyncratic reaction linked to HLA-B*57:01?

  • Acetaminophen hepatotoxicity
  • Abacavir hypersensitivity
  • Amoxicillin-induced diarrhea
  • Loop diuretic electrolyte loss

Correct Answer: Abacavir hypersensitivity

Q4. Which mechanism commonly underlies metabolic idiosyncratic reactions?

  • Excessive pharmacologic effect at therapeutic dose
  • Formation of reactive metabolites that bind proteins
  • Direct inhibition of renin–angiotensin system
  • Activation of PPAR receptors

Correct Answer: Formation of reactive metabolites that bind proteins

Q5. Which genetic factor is most often implicated in altered drug metabolism leading to idiosyncrasy?

  • HLA-B allele variations only
  • CYP450 polymorphisms such as CYP2C9, CYP2C19, CYP2D6
  • Variants in glucose transporters
  • Mutations in collagen genes

Correct Answer: CYP450 polymorphisms such as CYP2C9, CYP2C19, CYP2D6

Q6. Carbamazepine-induced Stevens–Johnson syndrome is strongly associated with which allele in certain populations?

  • HLA-B*15:02
  • HLA-B*57:01
  • CYP2D6*4
  • HLA-DR4

Correct Answer: HLA-B*15:02

Q7. Which clinical feature suggests an idiosyncratic hepatic reaction rather than predictable hepatotoxicity?

  • Onset immediately after a single massive overdose
  • Unpredictable latency with immune signs like fever and eosinophilia
  • Progressive elevation of AST/ALT proportional to dose
  • Pure cholestasis in every patient receiving the drug

Correct Answer: Unpredictable latency with immune signs like fever and eosinophilia

Q8. Which test can be used to reduce risk before prescribing abacavir?

  • Serum creatinine measurement
  • HLA-B*57:01 allele screening
  • CYP3A4 activity assay
  • Liver ultrasound

Correct Answer: HLA-B*57:01 allele screening

Q9. Why are animal models limited for predicting human idiosyncratic drug reactions?

  • Animals have identical HLA alleles to humans
  • Idiosyncrasy often depends on human-specific genetics and immune responses
  • Animals eliminate drugs faster, preventing any reactions
  • Animal studies are always more sensitive than human trials

Correct Answer: Idiosyncrasy often depends on human-specific genetics and immune responses

Q10. Which clinical management is appropriate on suspicion of a severe idiosyncratic reaction?

  • Continue the drug and monitor weekly
  • Immediate drug withdrawal and supportive care
  • Reduce dose by half and observe
  • Switch to a drug in the same class without evaluation

Correct Answer: Immediate drug withdrawal and supportive care

Q11. Which laboratory finding commonly accompanies drug-induced hemolysis due to idiosyncrasy?

  • Elevated troponin
  • Increased bilirubin and lactate dehydrogenase with low haptoglobin
  • Hypoglycemia with low insulin
  • Isolated high alkaline phosphatase only

Correct Answer: Increased bilirubin and lactate dehydrogenase with low haptoglobin

Q12. A patient develops fever, rash, lymphadenopathy, and eosinophilia after starting a drug. This constellation is best described as:

  • Type A reaction
  • Drug reaction with eosinophilia and systemic symptoms (DRESS)
  • Simple allergic rhinitis
  • Serotonin syndrome

Correct Answer: Drug reaction with eosinophilia and systemic symptoms (DRESS)

Q13. Which statement about dose relationship in idiosyncratic reactions is correct?

  • They are strictly dose-dependent and predictable from pharmacology
  • They are usually not related to the usual therapeutic dose
  • They only occur at toxic overdose levels
  • They can be prevented by dividing the daily dose

Correct Answer: They are usually not related to the usual therapeutic dose

Q14. Which tool or guideline helps translate pharmacogenetic test results into prescribing recommendations?

  • WHO Essential Medicines List
  • Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines
  • Merck Manual for veterinary medicine
  • Good Manufacturing Practice documents

Correct Answer: Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines

Q15. Which drug is a classic example of idiosyncratic hepatotoxicity linked to reactive metabolite formation?

  • Amoxicillin
  • Halothane
  • Metformin
  • Furosemide

Correct Answer: Halothane

Q16. Lymphocyte transformation test (LTT) is used to:

  • Measure renal clearance of drugs
  • Detect drug-specific T-cell proliferative responses in suspected immune idiosyncrasy
  • Quantify drug plasma concentration for therapeutic drug monitoring
  • Assess platelet function

Correct Answer: Detect drug-specific T-cell proliferative responses in suspected immune idiosyncrasy

Q17. Which preventive strategy is most effective for HLA-linked severe cutaneous adverse reactions?

  • Universal high-dose corticosteroid prophylaxis
  • Pre-prescription HLA allele screening in at-risk populations
  • Routine liver biopsy before therapy
  • Giving the drug with food

Correct Answer: Pre-prescription HLA allele screening in at-risk populations

Q18. Which property increases risk of a drug causing idiosyncratic reactions?

  • Drug is rapidly excreted unchanged
  • Drug forms reactive metabolites or binds covalently to proteins
  • Drug is administered topically only
  • Drug has 100% oral bioavailability with no metabolism

Correct Answer: Drug forms reactive metabolites or binds covalently to proteins

Q19. Rechallenge with the suspected drug after a severe idiosyncratic reaction is generally:

  • Recommended to confirm diagnosis in all cases
  • Contraindicated because it may cause more severe reactions
  • Safe if done at a lower dose
  • Required before reporting the event

Correct Answer: Contraindicated because it may cause more severe reactions

Q20. Which adverse reaction is an example of direct immune hemolysis triggered idiosyncratically?

  • G6PD deficiency hemolysis due to oxidative drugs
  • Heparin-induced thrombocytopenia mediated by antibodies
  • Vitamin C overdose causing hemolysis
  • Iron deficiency anemia

Correct Answer: Heparin-induced thrombocytopenia mediated by antibodies

Q21. In pharmacovigilance, idiosyncratic reactions are best detected by:

  • Preclinical rodent toxicology alone
  • Post-marketing surveillance and spontaneous adverse event reporting
  • Only randomized controlled trials with small sample sizes
  • In vitro solubility testing

Correct Answer: Post-marketing surveillance and spontaneous adverse event reporting

Q22. Which metabolic deficiency predisposes to hemolysis with sulfonamide or dapsone exposure?

  • Cytochrome c oxidase deficiency
  • Glucose-6-phosphate dehydrogenase (G6PD) deficiency
  • Phenylalanine hydroxylase deficiency
  • Methylmalonyl-CoA mutase deficiency

Correct Answer: Glucose-6-phosphate dehydrogenase (G6PD) deficiency

Q23. Which statement about biomarkers for idiosyncratic ADR prediction is true?

  • No biomarkers are useful; prediction is impossible
  • Both genetic (HLA, CYP alleles) and mechanistic biomarkers can stratify risk
  • Only serum electrolytes predict idiosyncrasy
  • Biomarkers always guarantee prevention of reactions

Correct Answer: Both genetic (HLA, CYP alleles) and mechanistic biomarkers can stratify risk

Q24. Abacavir hypersensitivity is best prevented by:

  • Administering abacavir with antihistamines
  • HLA-B*57:01 genotyping before therapy
  • Titrating the dose from low to high
  • Monitoring liver enzymes weekly

Correct Answer: HLA-B*57:01 genotyping before therapy

Q25. Which drug adverse event timeline is most suggestive of an idiosyncratic immune reaction?

  • Immediate anaphylaxis within seconds
  • Delayed onset after days to weeks with systemic features
  • Gradual dose-related side effects after months only
  • Effects occurring exclusively after drug discontinuation

Correct Answer: Delayed onset after days to weeks with systemic features

Q26. Which laboratory approach can identify reactive metabolites implicated in idiosyncrasy?

  • Mass spectrometry coupled with metabolic activation systems
  • Complete blood count only
  • Plain X-ray imaging
  • Electrocardiogram

Correct Answer: Mass spectrometry coupled with metabolic activation systems

Q27. Which of the following is a recommended role for pharmacists in preventing idiosyncratic ADRs?

  • Ignore patient genetic history as irrelevant
  • Perform medication review, counsel patients, and recommend pharmacogenetic testing when indicated
  • Always substitute brand drugs with generics without verification
  • Delay reporting suspected ADRs to gather more cases

Correct Answer: Perform medication review, counsel patients, and recommend pharmacogenetic testing when indicated

Q28. Which clinical trial limitation reduces detection of rare idiosyncratic reactions?

  • Large diverse population sizes
  • Short duration and limited sample size of preapproval trials
  • Inclusion of pharmacogenetic screening for all participants
  • Extensive post-marketing studies

Correct Answer: Short duration and limited sample size of preapproval trials

Q29. Which management step is specific to immune-mediated idiosyncratic reactions with systemic involvement?

  • Immediate dose doubling to overcome reaction
  • Consider systemic corticosteroids or immunosuppression when indicated
  • Ignore symptoms unless laboratory values worsen
  • Continue the drug with added antihypertensive therapy

Correct Answer: Consider systemic corticosteroids or immunosuppression when indicated

Q30. Which is true regarding reporting and learning from idiosyncratic ADRs?

  • Single-case reports are unhelpful and should be discarded
  • Spontaneous reports and case series can identify signals leading to risk mitigation
  • Manufacturers always detect all idiosyncratic risks during premarketing
  • Pharmacovigilance has no role in preventing future cases

Correct Answer: Spontaneous reports and case series can identify signals leading to risk mitigation

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