Anti-protozoal agents like metronidazole, tinidazole and ornidazole are essential nitroimidazole drugs encountered in B.Pharm curriculum and pharmacy practice. This concise, keyword-focused introduction outlines their mechanism of action (nitro‑group reduction to reactive intermediates causing DNA damage), pharmacokinetics (absorption, hepatic metabolism, half‑life differences), clinical uses (amoebiasis, giardiasis, trichomoniasis, anaerobic infections), major adverse effects (metallic taste, GI upset, peripheral neuropathy, CNS toxicity, disulfiram‑like reaction), resistance mechanisms and important drug interactions (warfarin, alcohol). Emphasis is on dosing implications, monitoring and patient counselling for safe use. These focused MCQs include mechanism, pharmacology, clinical use, adverse reactions, interactions and resistance relevant to B.Pharm examinations and pharmacy practice. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which statement best describes the primary mechanism of action of metronidazole, tinidazole and ornidazole?
- Inhibition of bacterial cell wall synthesis
- Reduction of the nitro group to reactive intermediates causing DNA strand breakage
- Competitive antagonism of folate synthesis enzymes
- Blockade of protein synthesis at the 30S ribosomal subunit
Correct Answer: Reduction of the nitro group to reactive intermediates causing DNA strand breakage
Q2. Nitroimidazoles are most active against which type of organisms?
- Aerobic gram-positive cocci
- Aerobic gram-negative bacilli
- Anaerobic bacteria and protozoa
- Obligate intracellular bacteria
Correct Answer: Anaerobic bacteria and protozoa
Q3. What is the approximate elimination half-life of metronidazole in adults?
- 2 hours
- 8 hours
- 24 hours
- 48 hours
Correct Answer: 8 hours
Q4. Compared with metronidazole, tinidazole is characterized by:
- A much shorter half-life making it unsuitable for single-dose therapy
- A longer half-life that allows single-dose regimens for some infections
- No activity against protozoa
- Complete renal excretion unchanged
Correct Answer: A longer half-life that allows single-dose regimens for some infections
Q5. Which of the following is a primary protozoal indication for nitroimidazole therapy?
- Malaria (Plasmodium falciparum)
- Trichomoniasis (Trichomonas vaginalis)
- Leishmaniasis
- Toxoplasmosis
Correct Answer: Trichomoniasis (Trichomonas vaginalis)
Q6. Co‑administration of alcohol with metronidazole can produce which characteristic reaction?
- Serotonin syndrome
- Disulfiram‑like reaction (flushing, tachycardia, nausea)
- Severe hypoglycaemia
- Acute renal failure
Correct Answer: Disulfiram‑like reaction (flushing, tachycardia, nausea)
Q7. A clinically important interaction between metronidazole and warfarin typically results in:
- Reduced warfarin anticoagulant effect and thrombosis risk
- No interaction
- Increased INR and bleeding risk
- Increased metabolism of warfarin leading to lower INR
Correct Answer: Increased INR and bleeding risk
Q8. Which adverse effect is classically associated with prolonged nitroimidazole therapy?
- Progressive renal failure
- Peripheral neuropathy (numbness, paresthesia)
- Irreversible hearing loss
- Cardiac arrhythmias as common toxicity
Correct Answer: Peripheral neuropathy (numbness, paresthesia)
Q9. Regarding use in pregnancy, which statement is most appropriate for metronidazole?
- Strictly contraindicated in all trimesters
- Generally considered safe and used when benefits outweigh risks
- Only topical forms are permitted; oral forms are banned
- Causes specific fetal malformations and is never used
Correct Answer: Generally considered safe and used when benefits outweigh risks
Q10. A common mechanism of resistance to nitroimidazoles in protozoa involves:
- Increased drug uptake through porins
- Mutations reducing activity of pyruvate:ferredoxin oxidoreductase (PFOR) and decreased drug activation
- Overproduction of dihydropteroate synthase
- Acquisition of beta‑lactamase enzymes
Correct Answer: Mutations reducing activity of pyruvate:ferredoxin oxidoreductase (PFOR) and decreased drug activation
Q11. Which laboratory parameter should be monitored during prolonged metronidazole therapy?
- Serum amylase only
- Liver function tests (ALT/AST, bilirubin)
- Thyroid function tests
- Fasting blood glucose exclusively
Correct Answer: Liver function tests (ALT/AST, bilirubin)
Q12. The primary elimination pathway for metronidazole is best described as:
- Excreted unchanged primarily in feces
- Hepatic metabolism with renal excretion of metabolites
- Complete biliary excretion of the parent drug
- Elimination only by pulmonary exhalation
Correct Answer: Hepatic metabolism with renal excretion of metabolites
Q13. Which nitroimidazole is classically associated with a metallic taste as a common adverse effect?
- Tinidazole
- Metronidazole
- Ornidazole
- None of the nitroimidazoles cause metallic taste
Correct Answer: Metronidazole
Q14. Nitroimidazoles are generally considered:
- Bacteriostatic agents
- Bactericidal agents
- Fungistatic agents
- Antiviral agents
Correct Answer: Bactericidal agents
Q15. Which enzyme system in anaerobic organisms donates electrons that help reduce the nitro group of metronidazole?
- NADPH oxidase
- Pyruvate:ferredoxin oxidoreductase (PFOR) / ferredoxin electron transport
- Ribonucleotide reductase
- Cytochrome P450 reductase
Correct Answer: Pyruvate:ferredoxin oxidoreductase (PFOR) / ferredoxin electron transport
Q16. A commonly used single‑dose regimen for tinidazole in trichomoniasis is:
- 500 mg once daily for 7 days
- 2 g single oral dose
- Intravenous infusion over 24 hours
- Topical vaginal gel only
Correct Answer: 2 g single oral dose
Q17. Which statement about ornidazole is correct compared with metronidazole?
- Ornidazole has a significantly shorter half-life than metronidazole
- Ornidazole is not active against anaerobic bacteria
- Ornidazole has a longer half-life and broadly similar adverse effects
- Ornidazole causes no CNS toxicity even with prolonged use
Correct Answer: Ornidazole has a longer half-life and broadly similar adverse effects
Q18. Which nitroimidazole is most commonly implicated in a clinically significant disulfiram‑like interaction with ethanol?
- Metronidazole
- Tinidazole
- Ornidazole
- All nitroimidazoles are free of this interaction
Correct Answer: Metronidazole
Q19. Nitroimidazoles are NOT effective for treatment of which of the following infections?
- Anaerobic abscesses
- Giardiasis
- Plasmodium falciparum malaria
- Entamoeba histolytica liver abscess
Correct Answer: Plasmodium falciparum malaria
Q20. The cytotoxic effect of activated nitroimidazole metabolites primarily results from:
- Inhibition of peptidoglycan crosslinking
- Alkylation and breakage of microbial DNA
- Blocking folate uptake at the cell membrane
- Chelation of intracellular iron stores
Correct Answer: Alkylation and breakage of microbial DNA
Q21. A patient on warfarin starts metronidazole. What monitoring change is most appropriate?
- No monitoring required
- Decrease frequency of INR testing
- Increase frequency of INR testing due to potential elevation
- Stop warfarin immediately
Correct Answer: Increase frequency of INR testing due to potential elevation
Q22. Which neurological adverse effect has been reported with high doses or prolonged use of metronidazole?
- Peripheral neuropathy and seizures/encephalopathy
- Progressive blindness within 24 hours
- Acute psychosis in all patients
- Permanent cerebellar infarction
Correct Answer: Peripheral neuropathy and seizures/encephalopathy
Q23. Which nitroimidazole is commonly available in intravenous formulation for severe anaerobic infections?
- Metronidazole
- Tinidazole only oral
- Ornidazole only topical
- No nitroimidazoles have IV formulations
Correct Answer: Metronidazole
Q24. A principal active metabolite of metronidazole that contributes to activity is:
- Hydroxy‑metronidazole
- Metronidazole sulfate
- Ornidazole glucuronide
- Tinidazole phosphate
Correct Answer: Hydroxy‑metronidazole
Q25. Patient counselling for nitroimidazoles should include which instruction regarding alcohol?
- Alcohol can be consumed without restriction
- Avoid alcohol during therapy and for at least 48 hours after completion
- Only red wine should be avoided
- Alcohol must be avoided for 6 weeks after therapy
Correct Answer: Avoid alcohol during therapy and for at least 48 hours after completion
Q26. Nitroimidazoles are first‑line agents for which invasive protozoal infection?
- Cutaneous leishmaniasis
- Invasive amoebiasis (Entamoeba histolytica)
- Toxoplasma gondii encephalitis
- Trypanosoma cruzi infection
Correct Answer: Invasive amoebiasis (Entamoeba histolytica)
Q27. During therapy with metronidazole a patient develops new numbness and tingling in the feet. The pharmacist should:
- Ignore symptoms; they are unrelated
- Recommend immediate discontinuation and clinical review for peripheral neuropathy
- Suggest doubling the dose to overcome tolerance
- Advise alcohol consumption to reduce side effects
Correct Answer: Recommend immediate discontinuation and clinical review for peripheral neuropathy
Q28. The selectivity of nitroimidazoles for anaerobic organisms is mainly due to:
- Higher membrane permeability in aerobes
- Requirement for low redox potential and specific electron transport to activate the drug in anaerobes
- Binding to mammalian ribosomes selectively
- Preferential uptake by macrophages
Correct Answer: Requirement for low redox potential and specific electron transport to activate the drug in anaerobes
Q29. The oral bioavailability of metronidazole is approximately:
- 10%
- 40%
- 70%
- 100%
Correct Answer: 100%
Q30. Which clinical feature would most strongly suggest the need to stop nitroimidazole therapy and seek urgent review?
- Mild transient headache
- Onset of progressive numbness, ataxia or severe confusion
- Mild metallic taste on the tongue
- Temporary mild nausea after the first dose
Correct Answer: Onset of progressive numbness, ataxia or severe confusion
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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