Nalidixic acid is a first-generation quinolone antibiotic important for B.Pharm students studying medicinal chemistry and pharmacology. Its chemistry centers on the 4-oxo-1,4-dihydroquinoline-3-carboxylic framework; understanding structure–activity relationships, synthesis, physicochemical properties, and analytical methods links molecular design to pharmacological action. Nalidixic acid inhibits bacterial DNA gyrase (topoisomerase II), producing bactericidal effects against many Gram-negative urinary pathogens, while resistance arises from gyrA mutations, qnr genes, and efflux. Clinical uses, pharmacokinetics, adverse effects, drug interactions, and stability considerations are essential for therapeutics and quality control. Study these MCQs to strengthen recall and application. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which chemical class does nalidixic acid belong to?
- Quinolone antibiotic
- Fluoroquinolone antibiotic
- Tetracycline antibiotic
- Beta-lactam antibiotic
Correct Answer: Quinolone antibiotic
Q2. Nalidixic acid primarily targets which bacterial enzyme?
- DNA gyrase (topoisomerase II)
- RNA polymerase
- Peptidyl transferase
- Cell wall transpeptidase
Correct Answer: DNA gyrase (topoisomerase II)
Q3. Nalidixic acid is classified as which generation of quinolones?
- First-generation
- Second-generation
- Third-generation
- Fourth-generation
Correct Answer: First-generation
Q4. Historically, nalidixic acid has been most commonly used to treat which condition?
- Uncomplicated urinary tract infections
- Community-acquired pneumonia
- Methicillin-resistant Staphylococcus aureus infections
- Systemic fungal infections
Correct Answer: Uncomplicated urinary tract infections
Q5. The bactericidal action of nalidixic acid results from which mechanism?
- Stabilization of DNA–topoisomerase complex leading to double-strand DNA breaks
- Inhibition of peptidoglycan cross-linking
- Disruption of bacterial membrane integrity by pore formation
- Inhibition of protein synthesis at the 30S ribosomal subunit
Correct Answer: Stabilization of DNA–topoisomerase complex leading to double-strand DNA breaks
Q6. High-level resistance to nalidixic acid is most commonly associated with mutations in which gene?
- gyrA
- rpoB
- mecA
- ermB
Correct Answer: gyrA
Q7. Which plasmid-mediated mechanism can reduce nalidixic acid susceptibility?
- qnr proteins that protect DNA gyrase
- Beta-lactamase production
- Aminoglycoside-modifying enzymes
- Methylation of 23S rRNA
Correct Answer: qnr proteins that protect DNA gyrase
Q8. What is the primary route of elimination for nalidixic acid?
- Renal excretion
- Hepatobiliary excretion
- Exhalation via lungs
- Skin secretion
Correct Answer: Renal excretion
Q9. Nalidixic acid shows best in vitro activity against which group of organisms?
- Enterobacteriaceae (Gram-negative bacilli)
- Anaerobic Gram-positive cocci
- Protozoa
- Mycobacteria
Correct Answer: Enterobacteriaceae (Gram-negative bacilli)
Q10. Which statement about nalidixic acid and Pseudomonas aeruginosa is correct?
- It has limited or poor activity against Pseudomonas aeruginosa
- It is the drug of choice for Pseudomonas infections
- It universally eradicates Pseudomonas at low concentrations
- It is primarily used for Pseudomonas prophylaxis
Correct Answer: It has limited or poor activity against Pseudomonas aeruginosa
Q11. Which patient population is generally advised to avoid nalidixic acid due to safety concerns?
- Children and pregnant women because of potential cartilage effects
- Middle-aged adults with controlled hypertension
- Patients with hyperthyroidism
- Adults receiving vitamin supplements
Correct Answer: Children and pregnant women because of potential cartilage effects
Q12. Which analytical technique is commonly used for assay and purity testing of nalidixic acid in formulations?
- High-performance liquid chromatography with UV detection
- Gas chromatography–mass spectrometry without derivatization
- Nuclear magnetic resonance for routine QC quantification
- Flame photometry
Correct Answer: High-performance liquid chromatography with UV detection
Q13. Which functional group in nalidixic acid primarily contributes to its acidic behavior and ionization?
- Carboxylic acid group
- Primary amine group
- Thiol group
- Ether linkage
Correct Answer: Carboxylic acid group
Q14. Which core structural motif is characteristic of nalidixic acid and other quinolones?
- 4-oxo-1,4-dihydroquinoline-3-carboxylic acid core
- Beta-lactam ring fused to a thiazolidine
- Tetracyclic polyketide backbone
- Macrolide lactone ring
Correct Answer: 4-oxo-1,4-dihydroquinoline-3-carboxylic acid core
Q15. Nalidixic acid exhibits which of the following bacteriological effects?
- Bactericidal activity against susceptible organisms
- Strictly bacteriostatic activity only
- Only inhibits toxin production without affecting growth
- Only promotes bacterial sporulation
Correct Answer: Bactericidal activity against susceptible organisms
Q16. Co-administration of nalidixic acid with which of the following is likely to reduce its oral absorption?
- Antacids containing magnesium or aluminum
- Vitamin C supplements
- Paracetamol (acetaminophen)
- Oral contraceptives without antacid components
Correct Answer: Antacids containing magnesium or aluminum
Q17. Nalidixic acid shows decreased chemical stability under which condition?
- Strongly alkaline pH
- Weakly acidic pH
- Refrigerated, dark conditions
- Desiccated, room-temperature storage
Correct Answer: Strongly alkaline pH
Q18. Why is ultraviolet (UV) detection suitable for nalidixic acid analysis in HPLC?
- Because nalidixic acid has a conjugated aromatic system with strong UV absorbance
- Because nalidixic acid is volatile and ionizes in the gas phase
- Because nalidixic acid emits visible fluorescence without derivatization
- Because nalidixic acid contains heavy metals detectable by UV
Correct Answer: Because nalidixic acid has a conjugated aromatic system with strong UV absorbance
Q19. Which quality control parameter is routinely checked for nalidixic acid raw material and tablets?
- Assay by HPLC to determine active content
- Cholesterol level in formulation
- Presence of live bacterial contaminants as potency indicator
- Radioactivity level
Correct Answer: Assay by HPLC to determine active content
Q20. In which dosage form is nalidixic acid most commonly administered clinically?
- Oral tablets
- Topical ointment for skin application
- Inhalation aerosol
- Intravenous lipid emulsion
Correct Answer: Oral tablets
Q21. Due to its relatively short elimination half-life, nalidixic acid dosing is often scheduled as which frequency?
- Twice daily dosing
- Once weekly dosing
- Once monthly dosing
- Continuous infusion only
Correct Answer: Twice daily dosing
Q22. Which common adverse effect should students consider when counseling patients on nalidixic acid?
- Gastrointestinal upset (nausea, vomiting)
- Marked hyperglycemia in all patients
- Hair loss within hours of first dose
- Immediate anaphylactic shock in every patient
Correct Answer: Gastrointestinal upset (nausea, vomiting)
Q23. Is nalidixic acid recommended during pregnancy?
- No — generally avoided due to potential cartilage and bone effects in the fetus
- Yes — it is the preferred antibiotic in pregnancy
- Yes — but only as an injectable form during labor
- No — because it causes teratogenic neural tube defects specifically
Correct Answer: No — generally avoided due to potential cartilage and bone effects in the fetus
Q24. Introduction of a fluorine atom at the C-6 position of quinolone nucleus typically results in what effect?
- Conversion to fluoroquinolones with increased potency and broadened spectrum
- Complete loss of antibacterial activity
- Selective activity only against Gram-positive anaerobes
- Transformation into a macrolide-like molecule
Correct Answer: Conversion to fluoroquinolones with increased potency and broadened spectrum
Q25. Which laboratory method is the reference standard for determining nalidixic acid minimum inhibitory concentration (MIC)?
- Broth microdilution susceptibility testing
- Thromboplastin time assay
- ELISA for drug antigen
- Gram staining intensity measurement
Correct Answer: Broth microdilution susceptibility testing
Q26. A common amino acid substitution associated with nalidixic acid resistance in gyrA is:
- Serine to leucine at position 83 (Ser83→Leu)
- Alanine to valine at position 50 (Ala50→Val)
- Lysine to glutamate at position 200 (Lys200→Glu)
- Glycine to proline at position 10 (Gly10→Pro)
Correct Answer: Serine to leucine at position 83 (Ser83→Leu)
Q27. Which efflux system in Enterobacteriaceae is often implicated in decreased nalidixic acid susceptibility?
- AcrAB-TolC efflux pump
- P-glycoprotein in human gut epithelium
- ABC transporter specific for peptides
- Na+/K+ ATPase
Correct Answer: AcrAB-TolC efflux pump
Q28. How effective is nalidixic acid against obligate anaerobic bacteria?
- It generally has poor activity against obligate anaerobes
- It is the first-line agent for anaerobic infections
- It specifically enhances anaerobe growth
- It is active only when combined with antifungals
Correct Answer: It generally has poor activity against obligate anaerobes
Q29. For long-term stability of nalidixic acid tablets, which storage condition is recommended?
- Store in a cool, dry place protected from light
- Store in direct sunlight at high humidity
- Store submerged in saline solution
- Store in an open container at high temperature
Correct Answer: Store in a cool, dry place protected from light
Q30. Which analytical approach is most suitable for routine content uniformity and assay of nalidixic acid in finished tablets?
- Reversed-phase HPLC with UV detection
- Colorimetric spot test on filter paper
- Gram staining of tablet powder
- Measuring tablet buoyancy in water
Correct Answer: Reversed-phase HPLC with UV detection
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.
Mail- Sachin@pharmacyfreak.com