Preservation of pharmaceuticals using antimicrobial agents MCQs With Answer

Preservation of pharmaceuticals using antimicrobial agents MCQs With Answer

Preservation of pharmaceuticals using antimicrobial agents is crucial for B. Pharm students to ensure product safety, potency, and shelf-life. This topic covers types of preservatives (parabens, phenolics, quaternary ammonium compounds, organic acids), mechanisms of action, factors affecting efficacy (pH, concentration, formulation excipients), compatibility, regulatory limits, and preservative efficacy testing (PET/USP <51>). Understanding microbial challenge organisms, resistance issues, and preservative selection for topical, oral, ophthalmic, and parenteral forms is essential for rational formulation design. Mastery of these concepts helps prevent contamination, maintain stability, and meet quality standards. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary purpose of antimicrobial preservatives in multi-dose pharmaceutical formulations?

• To enhance taste of oral liquids
• To prevent microbial growth in multi-dose formulations
• To act as primary active pharmaceutical ingredient
• To increase drug solubility

Correct Answer: To prevent microbial growth in multi-dose formulations

Q2. Which of the following is a commonly used paraben preservative?

• Benzalkonium chloride
• Methylparaben
• Chlorhexidine
• Phenylmercuric acetate

Correct Answer: Methylparaben

Q3. Which preservative is a quaternary ammonium compound often used in ophthalmic solutions?

• Propylparaben
• Benzalkonium chloride
• Sodium benzoate
• Thimerosal

Correct Answer: Benzalkonium chloride

Q4. The preservative efficacy test (PET) as per USP is primarily used to assess what?

• Solubility of preservatives
• Antimicrobial potency of active drug
• Ability of formulation to reduce microbial counts over time
• Sensory properties of preservatives

Correct Answer: Ability of formulation to reduce microbial counts over time

Q5. Which organisms are standard challenge microorganisms in preservative efficacy testing?

• Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, Aspergillus brasiliensis
• Escherichia coli only
• Mycobacterium tuberculosis and Clostridium botulinum
• Lactobacillus spp. and Bifidobacterium spp.

Correct Answer: Staphylococcus aureus, Pseudomonas aeruginosa, Candida albicans, Aspergillus brasiliensis

Q6. Which factor most significantly affects the activity of weak acid preservatives like benzoic and sorbic acid?

• Packaging color
• pH of the formulation
• Ambient light intensity
• Viscosity only

Correct Answer: pH of the formulation

Q7. How do chelating agents like EDTA enhance preservative activity?

• By directly killing microbes through oxidative stress
• By chelating metal ions that stabilize bacterial membranes, enhancing preservative penetration
• By increasing viscosity of the formulation
• By acting as additional preservatives themselves

Correct Answer: By chelating metal ions that stabilize bacterial membranes, enhancing preservative penetration

Q8. Which preservative is commonly used in oral syrups due to its effectiveness at low pH?

• Potassium sorbate
• Chlorobutanol
• Parabens
• Formaldehyde

Correct Answer: Potassium sorbate

Q9. Which statement best distinguishes preservatives from sterilization?

• Preservatives sterilize parenteral products
• Preservatives prevent microbial growth over time; sterilization aims to eliminate all viable microbes
• Preservatives increase product temperature
• Sterilization uses preservatives to maintain sterility

Correct Answer: Preservatives prevent microbial growth over time; sterilization aims to eliminate all viable microbes

Q10. Which preservative is known for releasing formaldehyde over time and used rarely due to safety concerns?

• Imidazolidinyl urea
• Sodium benzoate
• Benzyl alcohol
• Propylene glycol

Correct Answer: Imidazolidinyl urea

Q11. What is Minimum Inhibitory Concentration (MIC) in preservative selection?

• The minimum dose that causes toxicity
• The lowest concentration of preservative that inhibits visible microbial growth
• The concentration that causes flavor change
• The maximum safe concentration in humans

Correct Answer: The lowest concentration of preservative that inhibits visible microbial growth

Q12. Which preservative class is especially effective against fungi in acidic formulations?

• Quaternary ammonium compounds
• Organic acids (e.g., sorbic, benzoic)
• Heavy metal salts
• Alcohols only

Correct Answer: Organic acids (e.g., sorbic, benzoic)

Q13. Which preservative is often used in parenteral multi-dose vials as antimicrobial agent at appropriate concentration?

• Thimerosal
• Benzyl alcohol
• Propylparaben
• Sodium benzoate

Correct Answer: Benzyl alcohol

Q14. Which preservative can be inactivated by anionic surfactants leading to reduced efficacy?

• Phenolic preservatives
• Benzalkonium chloride
• Propylparaben
• Sodium benzoate

Correct Answer: Benzalkonium chloride

Q15. Which preservative is suitable for ophthalmic drops but may cause ocular irritation with prolonged use?

• Sodium propionate
• Benzalkonium chloride
• Potassium sorbate
• Isopropyl alcohol

Correct Answer: Benzalkonium chloride

Q16. What is a major disadvantage of using parabens in formulations?

• Poor antimicrobial activity
• Potential for allergic reactions and phasing out due to safety concerns
• They are too volatile for stable formulations
• They only work at extremely high pH

Correct Answer: Potential for allergic reactions and phasing out due to safety concerns

Q17. Which preservative is an alcohol commonly used in oral and topical formulations for antimicrobial activity?

• Propylene glycol
• Ethanol
• Sodium benzoate
• Chlorobutanol

Correct Answer: Ethanol

Q18. For preservative effectiveness, which storage condition generally decreases preservative activity?

• Refrigeration
• High temperatures causing degradation
• Storage in amber glass
• Low humidity

Correct Answer: High temperatures causing degradation

Q19. Which preservative is especially effective against Gram-negative bacteria like Pseudomonas?

• Phenoxyethanol
• Potassium sorbate
• Methylparaben
• EDTA alone

Correct Answer: Phenoxyethanol

Q20. What role does pH play in the activity of benzoic acid as a preservative?

• Benzoic acid is most effective at high pH (>8)
• Benzoic acid is most effective in its unionized form at low pH
• pH has no effect on benzoic acid
• Benzoic acid requires neutral pH to work

Correct Answer: Benzoic acid is most effective in its unionized form at low pH

Q21. Which preservative is commonly used in vaccines historically but is now limited due to toxicity concerns?

• Thimerosal
• Benzyl alcohol
• Sorbic acid
• Phenol

Correct Answer: Thimerosal

Q22. Which method detects the actual preservative concentration in a formulation during stability testing?

• Organoleptic testing
• Analytical assay like HPLC
• Viscosity measurement
• Microscopy for particulates

Correct Answer: Analytical assay like HPLC

Q23. What is the likely effect of adding a high concentration of non-ionic surfactant to a preserved formulation?

• Always increases preservative activity
• Can either enhance or reduce preservative activity depending on interactions
• Has no interaction with preservatives
• Makes preservatives volatile

Correct Answer: Can either enhance or reduce preservative activity depending on interactions

Q24. Which preservative is often used in cosmetics and topical pharmaceuticals due to broad-spectrum activity and good skin tolerance?

• Chlorobutanol
• Phenoxyethanol
• Formaldehyde
• Sodium benzoate

Correct Answer: Phenoxyethanol

Q25. What does USP <51> address in pharmaceutical quality control?

• Methods for dissolution testing
• Preservative efficacy testing (antimicrobial effectiveness)
• Assay limits for active ingredients
• Packaging material selection

Correct Answer: Preservative efficacy testing (antimicrobial effectiveness)

Q26. Which preservative type can be inactivated by reacting with aldehyde-reactive excipients or compounds?

• Formaldehyde-releasing preservatives
• Parabens
• Organic acids
• Alcohols

Correct Answer: Formaldehyde-releasing preservatives

Q27. Which preservative is a halogenated alcohol historically used in injection formulations but limited by instability?

• Chlorobutanol
• Sodium benzoate
• Benzyl alcohol
• Thimerosal

Correct Answer: Chlorobutanol

Q28. What is an important consideration when selecting a preservative for protein or biologic formulations?

• Preservatives never interact with proteins
• Potential protein denaturation, aggregation and loss of activity
• Only color change matters
• Proteins prevent preservative action

Correct Answer: Potential protein denaturation, aggregation and loss of activity

Q29. Which test assesses preservative performance after repeated opening of a multi-dose container?

• Forced degradation test
• In-use or simulated-use preservative efficacy test
• Sterility test only
• Photostability test

Correct Answer: In-use or simulated-use preservative efficacy test

Q30. Which preservative is commonly used in acidic beverage-type oral liquids?

• Sodium benzoate
• Benzalkonium chloride
• Chlorhexidine
• Imidazolidinyl urea

Correct Answer: Sodium benzoate

Q31. Which preservative mechanism primarily disrupts microbial cell membranes?

• DNA intercalation
• Membrane-active agents like quaternary ammonium compounds
• Chelation of metal ions
• pH buffering

Correct Answer: Membrane-active agents like quaternary ammonium compounds

Q32. Why might a preservative show reduced efficacy in the presence of organic matter?

• Organic matter enhances preservative potency
• Preservative binds to organic load, reducing free active concentration available to act on microbes
• Organic matter causes immediate sterilization
• It increases preservative solubility

Correct Answer: Preservative binds to organic load, reducing free active concentration available to act on microbes

Q33. Which preservative is frequently used in nasal drops but may raise irritation concerns?

• Phenoxyethanol
• Benzalkonium chloride
• Sorbic acid
• Sodium benzoate

Correct Answer: Benzalkonium chloride

Q34. What is the effect of temperature on preservative efficacy and stability?

• Higher temperature always increases preservative efficacy without degradation
• Elevated temperature can both increase antimicrobial activity and accelerate preservative degradation
• Temperature has no impact
• Only freezing affects preservatives

Correct Answer: Elevated temperature can both increase antimicrobial activity and accelerate preservative degradation

Q35. Which preservative is an aromatic alcohol often used in injectables and topical products?

• Benzyl alcohol
• Propylparaben
• Sodium benzoate
• EDTA

Correct Answer: Benzyl alcohol

Q36. What is a preservative’s ‘spectrum of activity’?

• The color range of the preservative
• The range of microorganisms (Gram-positive, Gram-negative, fungi) it can inhibit
• Its boiling point range
• Its solubility limits

Correct Answer: The range of microorganisms (Gram-positive, Gram-negative, fungi) it can inhibit

Q37. Which preservative may form esters with ethanol causing loss of activity in alcoholic formulations?

• Sorbic acid
• Methylparaben
• Chlorobutanol
• Sodium benzoate

Correct Answer: Sorbic acid

Q38. How can packaging affect preservative performance?

• No effect; packaging is irrelevant
• Interactions with container materials can adsorb or inactivate preservatives, and headspace/air ingress affects efficacy
• Packaging only affects appearance
• Only colored packaging matters

Correct Answer: Interactions with container materials can adsorb or inactivate preservatives, and headspace/air ingress affects efficacy

Q39. What is preservative breakthrough?

• When a preservative causes color change
• When microbes overcome the preservative and proliferate in the formulation
• When preservatives volatilize completely
• When preservative concentration increases over time

Correct Answer: When microbes overcome the preservative and proliferate in the formulation

Q40. Which analytical approach can be used to monitor preservative degradation products?

• HPLC with appropriate detection
• Only organoleptic assessment
• pH meter solely
• Microscopic counting

Correct Answer: HPLC with appropriate detection

Q41. Which preservative is effective over a wide pH range and often used in combination with others?

• Isopropyl alcohol
• Phenoxyethanol
• Benzoic acid
• Potassium sorbate

Correct Answer: Phenoxyethanol

Q42. Combining preservatives can result in which of the following?

• Only additive effects
• Additive, synergistic, or antagonistic interactions depending on chemistry
• Complete inactivation always
• Guaranteed toxicity

Correct Answer: Additive, synergistic, or antagonistic interactions depending on chemistry

Q43. Which preservative is commonly used in creams and lotions and acts as both preservative and solvent?

• Glycerin
• Propylene glycol
• EDTA
• Sodium benzoate

Correct Answer: Propylene glycol

Q44. What regulatory consideration is essential when selecting a preservative for pharmaceutical use?

• Only cost matters
• Approved types and maximum permitted concentrations in relevant pharmacopeias and guidelines
• Regulation does not apply to preservatives
• Only color approval is needed

Correct Answer: Approved types and maximum permitted concentrations in relevant pharmacopeias and guidelines

Q45. Which preservative class often shows reduced activity in high ionic strength (saline) environments?

• Organic acids
• Quaternary ammonium compounds
• Alcohols
• Formaldehyde-releasers

Correct Answer: Quaternary ammonium compounds

Q46. In preservative efficacy testing, what is the acceptable outcome for bacteria after specified timepoints according to pharmacopeial criteria?

• Increase in bacterial counts is acceptable
• Specified log reductions in bacterial counts (e.g., ≥3 log reduction within 14 days) depending on product type
• No change in microbial counts required
• Only fungal counts are considered

Correct Answer: Specified log reductions in bacterial counts (e.g., ≥3 log reduction within 14 days) depending on product type

Q47. Which preservative is contraindicated in neonates due to risk of gasping syndrome?

• Benzalkonium chloride
• Benzyl alcohol
• Phenoxyethanol
• Sodium benzoate

Correct Answer: Benzyl alcohol

Q48. Which preservative can be used in alcoholic mouthwashes and contributes to antimicrobial effect along with alcohol?

• Benzyl alcohol
• Chlorhexidine
• Sodium benzoate
• Propylparaben

Correct Answer: Chlorhexidine

Q49. Why is preservative selection critical for ophthalmic formulations beyond antimicrobial activity?

• Only color matching matters for eyes
• Preservatives can cause ocular toxicity, irritation, or destabilize corneal cells affecting safety and tolerability
• Preservatives are irrelevant in ophthalmics
• They enhance tear production always

Correct Answer: Preservatives can cause ocular toxicity, irritation, or destabilize corneal cells affecting safety and tolerability

Q50. Which strategy is recommended when a formulation cannot be adequately preserved without compromising safety?

• Use the highest possible preservative concentration regardless of safety
• Use single-use (unit-dose) packaging or terminal sterilization instead of relying on preservatives
• Avoid any microbial testing
• Remove active ingredient to allow stronger preservatives

Correct Answer: Use single-use (unit-dose) packaging or terminal sterilization instead of relying on preservatives

G S Sachin

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