Tetracycline – structure and degradation MCQs With Answer

Tetracycline – structure and degradation MCQs With Answer

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Tetracycline – structure and degradation MCQs With Answer provides B.Pharm students a focused, practical review of tetracycline chemistry, stability, and decomposition pathways. This introduction highlights key concepts: the tetracycline naphthacene core, the crucial C-4 dimethylamino group, keto-enol and phenolic functionalities, and common degradation routes such as epimerization, dehydration (anhydrotetracycline), hydrolysis, and photodegradation. Emphasis is placed on factors affecting stability—pH, light, heat, metal ion chelation—and analytical detection by HPLC, LC-MS and UV. Understanding degradation kinetics, impurity profiles and storage considerations is essential for formulation and quality control. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which structural feature of tetracycline is primarily responsible for its antibiotic activity and is prone to epimerization?

  • The C-4 dimethylamino group
  • The phenolic hydroxyl at C-10
  • The keto-enol system at C-11–C-12
  • The amide moiety on the D-ring

Correct Answer: The C-4 dimethylamino group

Q2. The tetracycline skeleton is best described as:

  • A five-membered lactone ring system
  • A fused four-ring naphthacene core
  • A benzene ring with a side-chain amide
  • A steroid-like tetracyclic terpenoid

Correct Answer: A fused four-ring naphthacene core

Q3. Epimerization of tetracycline at C-4 leads to which major product that has reduced antibacterial activity?

  • Oxytetracycline
  • 4-epitetracycline
  • Anhydrotetracycline
  • Demethylchlortetracycline

Correct Answer: 4-epitetracycline

Q4. Formation of anhydrotetracycline commonly occurs through which mechanism?

  • Oxidative cleavage of the A-ring
  • Dehydration between hydroxyl and adjacent carbon atoms
  • Alkylation of the dimethylamino group
  • Hydrogenation of the keto-enol system

Correct Answer: Dehydration between hydroxyl and adjacent carbon atoms

Q5. Which environmental condition most accelerates tetracycline photodegradation?

  • Low humidity in dark storage
  • Exposure to visible or UV light
  • Storage at 4 °C in amber vials
  • Presence of non-reactive sugars

Correct Answer: Exposure to visible or UV light

Q6. Chelation of tetracycline with divalent metal ions (e.g., Ca2+, Mg2+) primarily causes:

  • Increased solubility and faster dissolution
  • Formation of insoluble complexes and reduced bioavailability
  • Prevention of epimerization reactions
  • Conversion into a more potent antibiotic

Correct Answer: Formation of insoluble complexes and reduced bioavailability

Q7. Which analytical technique is most commonly used for quantitative assay and impurity profiling of tetracycline in formulations?

  • Gas chromatography with flame ionization detection (GC-FID)
  • High-performance liquid chromatography (HPLC)
  • Paper chromatography
  • Potentiometry

Correct Answer: High-performance liquid chromatography (HPLC)

Q8. Under strongly alkaline conditions, tetracycline degradation is typically:

  • Minimal due to stabilization by base
  • Accelerated, often with ring opening and cleavage reactions
  • Reversed to form the parent compound
  • Limited to simple salt formation only

Correct Answer: Accelerated, often with ring opening and cleavage reactions

Q9. The keto-enol tautomerism in tetracyclines influences which property most directly?

  • Optical rotation exclusively
  • Color, chelation behavior and pH-dependent stability
  • Solubility in organic solvents only
  • Evaporation temperature

Correct Answer: Color, chelation behavior and pH-dependent stability

Q10. Which degradation product of tetracycline has been associated with nephrotoxicity in literature and is a concern in formulations?

  • 4-epitetracycline
  • Anhydrotetracycline
  • Iso-tetracycline
  • Oxytetracycline

Correct Answer: Anhydrotetracycline

Q11. Rate kinetics of tetracycline degradation in dilute aqueous solution under excess oxidant or light is often modeled as:

  • Zero-order kinetics
  • First-order kinetics
  • Michaelis–Menten kinetics
  • Second-order kinetics exclusively

Correct Answer: First-order kinetics

Q12. Which formulation strategy can help minimize tetracycline photodegradation in a liquid formulation?

  • Packaging in clear glass bottles to show product color
  • Adding a photosensitizer
  • Using amber or opaque containers and adding antioxidants
  • Storing at elevated temperatures to accelerate equilibration

Correct Answer: Using amber or opaque containers and adding antioxidants

Q13. In a tetracycline stability study, monitoring which UV absorption change is most diagnostic for epimerization or conjugation changes?

  • Loss of a peak near 270–280 nm and change at 350–360 nm
  • Appearance of a peak at 2200 nm
  • Emergence of an IR band at 3200 cm−1 only
  • Complete loss of all UV absorption

Correct Answer: Loss of a peak near 270–280 nm and change at 350–360 nm

Q14. Which pH range generally offers the greatest chemical stability for many tetracycline molecules in aqueous solutions?

  • Strongly alkaline pH > 10
  • Neutral pH around 7–8
  • Moderately acidic pH around 2–4
  • Extremely acidic pH < 1

Correct Answer: Moderately acidic pH around 2–4

Q15. Which functional group on tetracycline is most involved in chelation with metal ions?

  • The aromatic methyl group
  • The enolic hydroxyl and adjacent keto groups
  • The tertiary carbon atoms
  • The terminal amide hydrogen only

Correct Answer: The enolic hydroxyl and adjacent keto groups

Q16. During forced degradation studies, which stress condition is most likely to produce anhydrotetracycline?

  • Photolysis in neutral buffered solution
  • Acidic hydrolysis or heating under acidic conditions
  • Storage under inert nitrogen at low temperature
  • Treatment with reducing agents such as NaBH4

Correct Answer: Acidic hydrolysis or heating under acidic conditions

Q17. Which degradation pathway decreases tetracycline’s chelating ability by modifying the enolic system?

  • Hydrogenation of the dimethylamino group
  • Oxidative cleavage of the enolic-keto motif
  • Methylation of aromatic hydrogens
  • Epimerization at C-4 only

Correct Answer: Oxidative cleavage of the enolic-keto motif

Q18. Analytical separation of tetracycline and its degradation products by reversed-phase HPLC typically requires:

  • Use of nonpolar mobile phases without aqueous buffer
  • Buffers to control pH and a gradient to resolve polar degradation products
  • High ionic strength salts to precipitate analytes
  • Neutral alumina column instead of C18

Correct Answer: Buffers to control pH and a gradient to resolve polar degradation products

Q19. Which preservative or excipient consideration can help reduce base-catalyzed degradation in a tetracycline oral suspension?

  • Using strong bases like NaOH as buffer
  • Maintaining a controlled mildly acidic pH with suitable buffering agents
  • Adding divalent metal salts at high concentration
  • Formulating with high ethanol content only

Correct Answer: Maintaining a controlled mildly acidic pH with suitable buffering agents

Q20. In forced degradation, identification of tetracycline impurities is most confidently achieved by which hyphenated technique?

  • UV spectroscopy alone
  • LC–MS/MS providing mass fragmentation and accurate mass
  • Thin-layer chromatography with visual inspection
  • Refractive index detection

Correct Answer: LC–MS/MS providing mass fragmentation and accurate mass

Q21. Epimerization of the dimethylamino center in tetracycline is stereochemical inversion at which type of carbon center?

  • Achiral sp2 carbon
  • Chiral sp3 carbon adjacent to an amine
  • Quaternary carbon with no hydrogens
  • Carboxylate carbon

Correct Answer: Chiral sp3 carbon adjacent to an amine

Q22. Which storage recommendation helps preserve solid tetracycline formulations?

  • Store at high temperature and humidity
  • Keep in airtight, light-protective containers at controlled room temperature
  • Expose to sunlight daily to maintain potency
  • Store mixed with alkaline powders to neutralize acids

Correct Answer: Keep in airtight, light-protective containers at controlled room temperature

Q23. Which of the following is NOT a common consequence of tetracycline interaction with metal cations in the gastrointestinal tract?

  • Reduced oral absorption
  • Formation of non-absorbable chelates
  • Increase in antibacterial potency systemically
  • Possible deposition in bones and teeth

Correct Answer: Increase in antibacterial potency systemically

Q24. Photodegradation of tetracycline can proceed through which initial photochemical event?

  • Homolytic cleavage of a C–C bond in the absence of light
  • Photoexcitation to singlet or triplet states leading to rearrangements
  • Spontaneous polymerization in the dark
  • Direct substitution of methyl groups by oxygen atoms

Correct Answer: Photoexcitation to singlet or triplet states leading to rearrangements

Q25. During product development, which impurity limit consideration is critical for tetracycline due to safety concerns?

  • Allowing unlimited levels of anhydro impurities
  • Setting specific impurity limits for anhydrotetracycline and epimers
  • Ignoring photostability because solids are always stable
  • Permitting metal contaminants at any level

Correct Answer: Setting specific impurity limits for anhydrotetracycline and epimers

Q26. Which change in chromatographic behavior would indicate formation of a more polar tetracycline degradation product?

  • Longer retention time on reversed-phase C18
  • Shorter retention time on reversed-phase C18
  • No change in retention time
  • Complete loss of UV detectability in all cases

Correct Answer: Shorter retention time on reversed-phase C18

Q27. Hydrolytic degradation of tetracycline in solution is influenced most strongly by:

  • Ambient barometric pressure
  • Solution pH, temperature and presence of catalysts
  • Concentration of inert gases like argon
  • Color of the container label

Correct Answer: Solution pH, temperature and presence of catalysts

Q28. What is a practical in-process control to reduce formation of epimers during tetracycline manufacturing?

  • Processing at uncontrolled high temperatures
  • Maintaining controlled pH and minimizing prolonged exposure to aqueous acidic or basic conditions
  • Adding excess divalent metals during synthesis
  • Deliberately exposing intermediates to sunlight

Correct Answer: Maintaining controlled pH and minimizing prolonged exposure to aqueous acidic or basic conditions

Q29. Which spectroscopic change might suggest conversion of tetracycline to anhydrotetracycline?

  • Shift or loss of UV bands associated with conjugated enone systems and a change in solution color
  • Appearance of a new IR band at 7000 cm−1
  • Increase in refractive index only
  • Complete disappearance of any absorbance below 200 nm

Correct Answer: Shift or loss of UV bands associated with conjugated enone systems and a change in solution color

Q30. Which regulatory guideline element is essential when reporting tetracycline stability data for marketing authorization?

  • Providing no forced degradation data
  • Comprehensive stability indicating method validation and degradation profiling
  • Only describing color changes without analytical quantification
  • Submitting only raw unprocessed chromatograms without system suitability

Correct Answer: Comprehensive stability indicating method validation and degradation profiling

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