Introduction: Didanosine, Zalcitabine and Lamivudine MCQs With Answer provide B. Pharm students a focused review of three nucleoside reverse transcriptase inhibitors (NRTIs) used in antiretroviral therapy. This short course covers mechanism of action, intracellular phosphorylation, pharmacokinetics, dose adjustments, drug interactions, resistance mutations (like M184V), adverse effects such as pancreatitis, peripheral neuropathy and mitochondrial toxicity, and clinical uses including lamivudine’s activity against hepatitis B virus. Emphasis is placed on monitoring parameters, formulation and historical context (zalcitabine withdrawal). The questions reinforce core concepts needed for pharmacy practice and exams. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which pharmacologic class do didanosine, zalcitabine and lamivudine belong to?
- Nucleoside reverse transcriptase inhibitors
- Nucleotide reverse transcriptase inhibitors
- Non-nucleoside reverse transcriptase inhibitors
- Protease inhibitors
Correct Answer: Nucleoside reverse transcriptase inhibitors
Q2. What is the primary mechanism of action of didanosine, zalcitabine and lamivudine?
- Inhibition of viral protease
- Chain termination of viral DNA after incorporation by reverse transcriptase
- Interference with viral entry into host cells
- Blocking viral integrase
Correct Answer: Chain termination of viral DNA after incorporation by reverse transcriptase
Q3. How are these nucleoside analogues activated inside host cells?
- Directly active without modification
- Converted to active triphosphate metabolites by cellular kinases
- Cleaved by viral proteases to active forms
- Activated only in the liver by CYP enzymes
Correct Answer: Converted to active triphosphate metabolites by cellular kinases
Q4. Which adverse effect is classically associated with didanosine (ddI)?
- Nephrolithiasis
- Pancreatitis
- QT prolongation
- Bone marrow suppression
Correct Answer: Pancreatitis
Q5. Zalcitabine (ddC) use was limited primarily because of which major toxicity?
- Cardiotoxicity
- Severe peripheral neuropathy
- Renal tubular acidosis
- Ototoxicity
Correct Answer: Severe peripheral neuropathy
Q6. Which of these drugs also has clinically significant activity against hepatitis B virus (HBV)?
- Didanosine
- Zalcitabine
- Lamivudine
- None of the above
Correct Answer: Lamivudine
Q7. Which agent requires dose adjustment in renal impairment due to predominant renal excretion?
- Didanosine
- Zalcitabine
- Lamivudine
- Efavirenz
Correct Answer: Lamivudine
Q8. Co-administration of tenofovir with didanosine commonly leads to which interaction?
- Decreased tenofovir levels with no effect on didanosine
- Increased didanosine exposure and higher toxicity risk
- Mutual inactivation of both drugs
- No clinically relevant interaction
Correct Answer: Increased didanosine exposure and higher toxicity risk
Q9. What is the current regulatory status of zalcitabine in most countries?
- First-line therapy for HIV
- Over-the-counter antiviral
- Withdrawn/discontinued due to toxicity
- Recommended for hepatitis C
Correct Answer: Withdrawn/discontinued due to toxicity
Q10. Which toxicity arises from NRTI-induced mitochondrial dysfunction?
- Lactic acidosis with hepatic steatosis
- Pulmonary fibrosis
- Acute pancreatitis only in children
- Peripheral edema without metabolic changes
Correct Answer: Lactic acidosis with hepatic steatosis
Q11. Didanosine is a synthetic analogue of which natural nucleoside?
- Guanosine
- Adenosine
- Cytidine
- Thymidine
Correct Answer: Adenosine
Q12. What administration advice is important for didanosine tablets or powder?
- Take with high-fat meal to increase absorption
- Take on an empty stomach because gastric acidity degrades the drug
- Crush tablets and mix with citrus juices
- Always take with antacids to reduce GI upset
Correct Answer: Take on an empty stomach because gastric acidity degrades the drug
Q13. Which fixed-dose combination containing lamivudine was widely used (brand name Combivir)?
- Lamivudine + Zidovudine
- Lamivudine + Tenofovir
- Lamivudine + Efavirenz
- Lamivudine + Ritonavir
Correct Answer: Lamivudine + Zidovudine
Q14. The M184V mutation in HIV reverse transcriptase causes high-level resistance to which drug?
- Didanosine
- Zalcitabine
- Lamivudine
- Nevirapine
Correct Answer: Lamivudine
Q15. Which drug is most classically associated with both pancreatitis and peripheral neuropathy?
- Lamivudine
- Didanosine
- Zalcitabine
- Abacavir
Correct Answer: Didanosine
Q16. Which laboratory test is especially important to monitor when a patient is on didanosine?
- Serum creatine kinase
- Serum amylase and lipase
- Thyroid function tests
- Fasting blood glucose only
Correct Answer: Serum amylase and lipase
Q17. Among the three drugs, which is most commonly used in pregnancy as part of ART backbones?
- Zalcitabine
- Didanosine
- Lamivudine
- Stavudine
Correct Answer: Lamivudine
Q18. Lamivudine (3TC) is an analogue of which natural nucleoside?
- Adenosine
- Cytidine
- Guanosine
- Uridine
Correct Answer: Cytidine
Q19. Why is lamivudine favored in many combination regimens compared with zalcitabine?
- Lamivudine has higher renal toxicity
- Lamivudine has better potency, safety and resistance profile
- Zalcitabine has superior tolerability
- Zalcitabine is cheaper and more available
Correct Answer: Lamivudine has better potency, safety and resistance profile
Q20. The reason nucleoside analogues cause chain termination is because they lack which functional group?
- 5′ phosphate
- 3′ hydroxyl group on the sugar moiety
- 1′ carbon on the sugar
- 2′ oxygen of the base
Correct Answer: 3′ hydroxyl group on the sugar moiety
Q21. Which adverse event is a shared risk across many older NRTIs due to mitochondrial DNA polymerase inhibition?
- Hypoglycemia
- Lactic acidosis
- Acute pancreatitis only
- Pulmonary embolism
Correct Answer: Lactic acidosis
Q22. Zalcitabine therapy commonly produces which oral adverse effect?
- Gingival hyperplasia
- Oral ulceration and stomatitis
- Hypersalivation without lesions
- Teeth discoloration
Correct Answer: Oral ulceration and stomatitis
Q23. Rapid development of the M184V mutation after lamivudine use demonstrates which pharmacological concept?
- High genetic barrier to resistance
- Low barrier to resistance with rapid emergence of resistant virus
- No clinically relevant resistance
- Cross-protection against all NRTIs
Correct Answer: Low barrier to resistance with rapid emergence of resistant virus
Q24. If lamivudine is stopped in a patient co-infected with HBV, what clinical problem may occur?
- Immediate renal failure
- HBV flare with elevated hepatic transaminases
- Permanent resistance to all antivirals
- Permanent immunosuppression
Correct Answer: HBV flare with elevated hepatic transaminases
Q25. Which of these statements about zalcitabine is correct?
- It is a potent inhibitor of HIV protease
- It is a dideoxycytidine analogue causing chain termination
- It is primarily used for hepatitis B treatment
- It increases CYP3A4 activity markedly
Correct Answer: It is a dideoxycytidine analogue causing chain termination
Q26. Which nucleoside analogue is most often described as having the most favorable safety and tolerability profile among the three?
- Didanosine
- Zalcitabine
- Lamivudine
- Stavudine
Correct Answer: Lamivudine
Q27. The intracellular active form of lamivudine inhibits HIV reverse transcriptase by which mechanism?
- Competitive inhibition without incorporation into DNA
- Incorporation into viral DNA causing immediate chain termination
- Binding to viral envelope proteins
- Activation of host immune response only
Correct Answer: Incorporation into viral DNA causing immediate chain termination
Q28. Which monitoring parameter is especially relevant for patients on lamivudine who are co-infected with hepatitis B?
- Serum amylase monthly
- Periodic hepatic transaminases and HBV DNA levels
- Frequent pulmonary function tests
- Monthly ECG monitoring
Correct Answer: Periodic hepatic transaminases and HBV DNA levels
Q29. Which of the following best explains why zalcitabine was removed from many treatment guidelines?
- Excellent efficacy but prohibitive cost
- Marked neurotoxicity and low tolerability limiting clinical use
- Frequent beneficial drug–drug interactions
- Superior to all modern NRTIs and thus reserved
Correct Answer: Marked neurotoxicity and low tolerability limiting clinical use
Q30. For pharmacy practice, which statement about lamivudine is most important?
- It requires co-administration with allopurinol
- It is ineffective against HBV and should be avoided in co-infection
- It is commonly used in ART backbones, requires renal dose adjustment and has HBV activity
- It must be administered only intravenously
Correct Answer: It is commonly used in ART backbones, requires renal dose adjustment and has HBV activity
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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