Antiamoebic drugs are essential in treating amoebiasis caused mainly by Entamoeba histolytica. This concise guide focuses on metronidazole and related agents (tinidazole, ornidazole, secnidazole, paromomycin, iodoquinol, diloxanide) covering mechanisms, pharmacokinetics, spectrum, luminal versus tissue activity, resistance, drug interactions and adverse effects such as metallic taste, disulfiram-like reaction and neuropathy. Emphasis is placed on clinical use for intestinal and hepatic amoebiasis, sequencing of tissue and luminal therapy, and special situations like pregnancy and hepatic dysfunction. Keywords: metronidazole, nitroimidazole, luminal amoebicide, paromomycin, mechanism of action, adverse effects, drug interactions. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which chemical class does metronidazole belong to?
- Nitroimidazole
- Aminoglycoside
- Macrolide
- Sulfonamide
Correct Answer: Nitroimidazole
Q2. What is the primary mechanism of action of metronidazole against anaerobes and protozoa?
- Inhibition of cell wall synthesis
- Formation of reactive nitro radicals that damage DNA
- Blocking 30S ribosomal subunit and inhibiting protein synthesis
- Inhibition of folate synthesis enzymes
Correct Answer: Formation of reactive nitro radicals that damage DNA
Q3. The main causative organism of invasive amoebiasis is:
- Giardia lamblia
- Entamoeba histolytica
- Cryptosporidium parvum
- Trichomonas vaginalis
Correct Answer: Entamoeba histolytica
Q4. Which of the following is considered a tissue amoebicide (acts on invasive forms)?
- Metronidazole
- Paromomycin
- Iodoquinol
- Diloxanide furoate
Correct Answer: Metronidazole
Q5. Which drug is a luminal aminoglycoside used to eradicate intestinal cysts of E. histolytica?
- Paromomycin
- Tinidazole
- Metronidazole
- Chloroquine
Correct Answer: Paromomycin
Q6. Which adverse effect is characteristically associated with metronidazole when taken with alcohol?
- Disulfiram-like reaction
- Ototoxicity
- Rash only
- Hypoglycemia
Correct Answer: Disulfiram-like reaction
Q7. Prolonged use of nitroimidazoles can lead to which neurological toxicity?
- Peripheral neuropathy
- Seizures in all patients
- Parkinsonism
- Myasthenia gravis exacerbation
Correct Answer: Peripheral neuropathy
Q8. Metronidazole interacts with warfarin primarily by:
- Inducing CYP3A4 and decreasing warfarin levels
- Inhibiting warfarin metabolism and increasing INR
- Increasing vitamin K synthesis
- Enhancing renal excretion of warfarin
Correct Answer: Inhibiting warfarin metabolism and increasing INR
Q9. Which statement about metronidazole use in pregnancy reflects conventional caution in many formularies?
- It is absolutely contraindicated in all trimesters
- It is relatively avoided in the first trimester unless needed
- It is the drug of choice for pregnancy-associated amoebiasis without restrictions
- It is only used topically in pregnancy
Correct Answer: It is relatively avoided in the first trimester unless needed
Q10. Nitroimidazoles like metronidazole are active against which of the following?
- Aerobic Gram-positive cocci only
- Anaerobic bacteria and certain protozoa
- Fungal organisms exclusively
- All intracellular viruses
Correct Answer: Anaerobic bacteria and certain protozoa
Q11. Compared to metronidazole, tinidazole offers which practical advantage?
- Longer half-life allowing shorter or single-dose regimens
- Complete absence of metallic taste
- No interaction with alcohol
- Exclusively luminal activity
Correct Answer: Longer half-life allowing shorter or single-dose regimens
Q12. Paromomycin’s antiparasitic action is primarily due to:
- Inhibition of folate synthesis
- Binding to the 30S ribosomal subunit and inhibiting protein synthesis
- Generating free radicals that damage DNA
- Blocking microtubule formation
Correct Answer: Binding to the 30S ribosomal subunit and inhibiting protein synthesis
Q13. A known adverse effect of iodoquinol with prolonged use is:
- Thyroid dysfunction and optic neuropathy
- Severe hepatotoxicity in all patients
- Marked neutropenia universally
- Renal failure within 24 hours
Correct Answer: Thyroid dysfunction and optic neuropathy
Q14. Diloxanide furoate is classified as which type of antiamoebic?
- Luminal amoebicide
- Tissue amoebicide
- Systemic antibiotic for anaerobes
- Antifungal agent
Correct Answer: Luminal amoebicide
Q15. Appropriate management of an amoebic liver abscess typically includes:
- Metronidazole (systemic) followed by a luminal agent to eradicate cyst carriage
- Paromomycin alone for 3 days
- Iodoquinol alone administered intravenously
- No drug therapy; only surgical drainage is indicated
Correct Answer: Metronidazole (systemic) followed by a luminal agent to eradicate cyst carriage
Q16. The primary route of elimination for metronidazole is:
- Hepatic metabolism with renal excretion of metabolites
- Exclusive renal excretion of unchanged drug
- Exhalation through lungs unchanged
- Fecal elimination only
Correct Answer: Hepatic metabolism with renal excretion of metabolites
Q17. A documented resistance mechanism to nitroimidazoles in protozoa involves:
- Enhanced uptake of the drug into the cell
- Decreased activation of the drug due to reduced redox proteins
- Mutations increasing cell wall impermeability
- Overexpression of folate pathway enzymes
Correct Answer: Decreased activation of the drug due to reduced redox proteins
Q18. A common early adverse effect experienced by patients taking metronidazole is:
- Metallic taste
- Severe hair loss within hours
- Immediate hypotension after first dose
- Complete loss of appetite permanently
Correct Answer: Metallic taste
Q19. After completing metronidazole for invasive intestinal amoebiasis, which follow-up therapy is recommended to eliminate luminal cysts?
- Paromomycin for luminal eradication
- Repeat metronidazole only
- Oral amphotericin B
- No further therapy required
Correct Answer: Paromomycin for luminal eradication
Q20. Nitazoxanide exhibits antiprotozoal activity by inhibiting which pathway?
- Pyruvate:ferredoxin oxidoreductase–dependent electron transfer
- DNA gyrase
- Beta-lactamase enzymes
- Ergosterol synthesis
Correct Answer: Pyruvate:ferredoxin oxidoreductase–dependent electron transfer
Q21. Which clinical effect indicates a disulfiram-like interaction after alcohol ingestion with nitroimidazoles?
- Flushing, tachycardia and nausea
- Severe cough without other signs
- Peripheral edema only
- Pruritic rash limited to hands
Correct Answer: Flushing, tachycardia and nausea
Q22. Which laboratory monitoring is most relevant during prolonged metronidazole therapy?
- Liver function tests
- Serum potassium only
- Fasting blood glucose only
- Thyroid-stimulating hormone weekly
Correct Answer: Liver function tests
Q23. Secnidazole and tinidazole are clinically distinct from metronidazole mainly because they:
- Have longer half-lives allowing single-dose therapy for some infections
- Are completely free of neurotoxicity
- Are only effective topically
- Do not interact with warfarin
Correct Answer: Have longer half-lives allowing single-dose therapy for some infections
Q24. Which luminal antiamoebic is minimally absorbed and acts locally in the gut?
- Paromomycin
- Metronidazole
- Tinidazole
- Clindamycin
Correct Answer: Paromomycin
Q25. Long-term use of iodoquinol has been associated with which neuro-ophthalmic complication?
- Optic neuritis and visual impairment
- Immediate blindness after first dose
- Auditory hallucinations only
- Guillain–Barré syndrome universally
Correct Answer: Optic neuritis and visual impairment
Q26. Metronidazole is bactericidal against anaerobes by:
- DNA strand breakage after intracellular reductive activation
- Blocking peptidoglycan cross-linking
- Inhibiting the 50S ribosomal subunit
- Chelating divalent cations essential for growth
Correct Answer: DNA strand breakage after intracellular reductive activation
Q27. Metronidazole achieves good penetration into which body compartment, making it useful for certain central nervous system infections?
- Cerebrospinal fluid (CSF)
- Synovial fluid only
- Lens of the eye exclusively
- Bone marrow without crossing blood–brain barrier
Correct Answer: Cerebrospinal fluid (CSF)
Q28. Which nitroimidazole is commonly chosen for single-dose therapy due to its longer elimination half-life?
- Tinidazole
- Metronidazole
- Paromomycin
- Iodoquinol
Correct Answer: Tinidazole
Q29. Activation of metronidazole in susceptible protozoa depends on reduction by which electron carrier protein?
- Ferredoxin
- Cytochrome P450
- NADPH oxidase only
- Glutathione peroxidase
Correct Answer: Ferredoxin
Q30. Recommended sequence for treating invasive intestinal amoebiasis to prevent relapse is:
- Systemic metronidazole to eradicate trophozoites, followed by a luminal amoebicide
- Luminal amoebicide only, no systemic therapy needed
- Systemic antibiotics unrelated to amoebiasis alone
- No treatment because spontaneous cure is universal
Correct Answer: Systemic metronidazole to eradicate trophozoites, followed by a luminal amoebicide
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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