Monophasic liquids – Mouthwashes MCQs With Answer

Monophasic liquids like mouthwashes are clear, single-phase solutions designed for local action in the oral cavity. For B. Pharm students, understanding formulation science—actives (chlorhexidine, cetylpyridinium chloride, essential oils, fluoride), excipients (solubilizers, humectants, sweeteners), pH control, preservatives, and organoleptic optimization—is crucial. Mouthwash development involves solubilizing volatile oils, managing alcohol or alcohol-free systems, ensuring clarity, stability, and microbial control, and complying with pharmacopeial quality control (pH, assay, ethanol content, microbial limits). Patient-centric aspects include dosing (10–20 mL, 30–60 s), safety (do not swallow, staining risk), interactions (anionic surfactants vs. cationic actives), packaging selection, and labeling. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Mouthwashes are classified as which dosage form within monophasic liquids?

• Solutions intended for local action in the oral cavity
• Suspensions intended for systemic absorption
• Emulsions designed for sustained release
• Aerosols for pulmonary delivery

Correct Answer: Solutions intended for local action in the oral cavity

Q2. The term “substantivity” in chlorhexidine mouthwash refers to:

• Ability to foam in the presence of anionic surfactants
• Prolonged binding to oral tissues with sustained antimicrobial action
• Rapid systemic absorption after rinsing
• Enhanced sweet taste due to humectants

Correct Answer: Prolonged binding to oral tissues with sustained antimicrobial action

Q3. A commonly marketed concentration of chlorhexidine gluconate mouthwash for gingivitis is:

• 0.005% w/v
• 0.05% w/v
• 0.12% w/v
• 2% w/v

Correct Answer: 0.12% w/v

Q4. A notable adverse effect associated with chlorhexidine mouthwash is:

• Hypoglycemia
• Brown staining of teeth and tongue
• Severe systemic hypotension
• Dental enamel erosion due to alkalinity

Correct Answer: Brown staining of teeth and tongue

Q5. Cetylpyridinium chloride (CPC) in mouthwashes is best described as a:

• Nonionic surfactant used as a solubilizer
• Cationic quaternary ammonium antiseptic
• Anionic detergent used as a foaming agent
• Neutral buffer component

Correct Answer: Cationic quaternary ammonium antiseptic

Q6. The typical concentration of CPC in over-the-counter mouthwashes is approximately:

• 0.005% w/v
• 0.05% w/v
• 0.5% w/v
• 5% w/v

Correct Answer: 0.05% w/v

Q7. In alcohol-containing mouthwashes, ethanol primarily functions as a:

• Primary active antiseptic at low concentrations
• Cosolvent and flavor solubilizer
• Viscosity enhancer
• pH buffer

Correct Answer: Cosolvent and flavor solubilizer

Q8. For alcohol-free mouthwashes, which excipient is most suitable to solubilize essential oils?

• Polysorbate 20
• Calcium carbonate
• Magnesium stearate
• Talc

Correct Answer: Polysorbate 20

Q9. Which of the following acts primarily as a humectant in mouthwash formulations?

• Glycerin
• Menthol
• Eucalyptol
• Sodium lauryl sulfate

Correct Answer: Glycerin

Q10. The preferred pH range for most mouthwashes to balance stability, comfort, and enamel safety is:

• pH 2.0–3.0
• pH 4.0–5.0
• pH 5.5–7.0
• pH 9.0–10.5

Correct Answer: pH 5.5–7.0

Q11. A suitable preservative for an aqueous mouthwash formulated around pH 5.5 is:

• Sodium benzoate
• Sodium bicarbonate
• Calcium chloride
• Aluminum hydroxide

Correct Answer: Sodium benzoate

Q12. Which of the following is NOT an essential oil typically used as an active in antiseptic mouthwashes?

• Thymol
• Eucalyptol
• Methyl salicylate
• Chlorhexidine gluconate

Correct Answer: Chlorhexidine gluconate

Q13. A common daily fluoride mouthrinse concentration (as sodium fluoride) for caries prevention is:

• 0.005% w/v
• 0.05% w/v
• 0.5% w/v
• 2% w/v

Correct Answer: 0.05% w/v

Q14. Which statement best differentiates a gargle from a mouthwash?

• Gargles are swallowed, mouthwashes are not
• Gargles are directed to the pharynx, mouthwashes primarily to the oral cavity
• Gargles are emulsions, mouthwashes are suspensions
• Gargles contain no active ingredients

Correct Answer: Gargles are directed to the pharynx, mouthwashes primarily to the oral cavity

Q15. Which interaction can reduce the efficacy of cationic actives like chlorhexidine in mouthwashes?

• Co-administration with nonionic solubilizers
• Immediate use after brushing with anionic surfactant–containing toothpaste
• Use with fluoride rinses
• Use with humectants like sorbitol

Correct Answer: Immediate use after brushing with anionic surfactant–containing toothpaste

Q16. A typical counseling advice to minimize the chlorhexidine–toothpaste interaction is to:

• Swallow the mouthwash
• Space toothbrushing and chlorhexidine rinse by about 30 minutes
• Increase volume of rinse to 50 mL
• Lower pH of the mouthwash to 3

Correct Answer: Space toothbrushing and chlorhexidine rinse by about 30 minutes

Q17. Which of the following quality control tests is LEAST relevant for a mouthwash?

• Clarity and absence of particulates
• pH determination
• Disintegration time
• Assay of active ingredient

Correct Answer: Disintegration time

Q18. A practical consumer package for an essential oil–containing mouthwash that limits loss of volatiles and breakage is:

• Rigid PVC bottle with screw cap
• Amber Type I glass ampoule
• HDPE or PET bottle with child-resistant closure
• Open-mouthed polypropylene jar

Correct Answer: HDPE or PET bottle with child-resistant closure

Q19. A mandatory label statement for most OTC mouthwashes includes:

• “For intravenous use only”
• “Do not swallow; expectorate after use”
• “Store below 0°C”
• “Shake vigorously for 15 minutes before use”

Correct Answer: “Do not swallow; expectorate after use”

Q20. Typical dosing directions for many antiseptic mouthwashes advise:

• 5 mL for 10 seconds
• 10–15 mL for 30–60 seconds
• 50 mL for 5 minutes
• 1 mL for 2 seconds

Correct Answer: 10–15 mL for 30–60 seconds

Q21. Regarding microbial control in mouthwashes, which statement is most accurate?

• Antimicrobial actives always eliminate the need for microbial limits testing
• Preservatives are unnecessary in all mouthwashes
• Products must meet pharmacopeial microbial limits even if self-preserving
• Microbial growth is impossible in flavored aqueous systems

Correct Answer: Products must meet pharmacopeial microbial limits even if self-preserving

Q22. A recommended order of addition during manufacturing an essential oil mouthwash is:

• Combine all powders; add dye; fill bottles; then add water
• Solubilize flavor in ethanol/surfactant; dissolve sweetener in water with humectant; combine; adjust pH; make up volume; filter
• Heat water to 90°C; add menthol directly; cool; bottle unfiltered
• Add dye first to improve solubilization of oils

Correct Answer: Solubilize flavor in ethanol/surfactant; dissolve sweetener in water with humectant; combine; adjust pH; make up volume; filter

Q23. Which sweetener is preferred for sugar-free mouthwash to avoid caries risk?

• Sucrose
• Sodium saccharin
• Glucose
• Maltose

Correct Answer: Sodium saccharin

Q24. To slightly increase body and improve mouthfeel without forming a gel, a suitable polymer for mouthwashes is:

• Hydroxypropyl methylcellulose (HPMC) at low concentration
• Cross-linked polyacrylic acid at 2%
• Starch paste
• Carbomer neutralized to high viscosity

Correct Answer: Hydroxypropyl methylcellulose (HPMC) at low concentration

Q25. Which packaging material is least suitable for alcohol/essential oil mouthwashes due to sorption and plasticizer leaching risks?

• PVC
• HDPE
• PET
• Type III glass

Correct Answer: PVC

Q26. Oxygenating mouthwashes containing hydrogen peroxide act primarily by:

• Lowering saliva pH to remove plaque
• Releasing nascent oxygen that disrupts anaerobic bacteria and debris
• Forming a protective polymer film on enamel
• Chelating calcium from dental plaque

Correct Answer: Releasing nascent oxygen that disrupts anaerobic bacteria and debris

Q27. Excessive or prolonged use of hydrogen peroxide mouthwash can lead to:

• Permanent enamel hardening
• Oral mucosal irritation and delayed healing
• Systemic hypoxia
• Fluorosis

Correct Answer: Oral mucosal irritation and delayed healing

Q28. A suitable analytical technique to quantify ethanol content in a mouthwash during QC is:

• Thin-layer chromatography with iodine detection
• Gas chromatography
• Disintegration testing
• Polarized light microscopy

Correct Answer: Gas chromatography

Q29. Which excipient contributes a cooling sensation and flavor impact in mouthwashes?

• Sorbitol
• Menthol
• Triethanolamine
• Sodium citrate

Correct Answer: Menthol

Q30. Which habit increases the risk of extrinsic staining in patients using chlorhexidine mouthwash?

• Drinking water only
• Regular tea and coffee consumption
• Avoiding all chromogenic foods
• Using alcohol-free formulations

Correct Answer: Regular tea and coffee consumption

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