Monophasic liquids – Throat paints are viscous, single-phase solutions designed for local application to the oropharyngeal mucosa. For B. Pharm students, this topic links core pharmaceutics with practical extemporaneous compounding. Key formulation elements include glycerin/propylene glycol/ethanol vehicles, viscosity and mucoadhesion for prolonged residence, suitable actives (antiseptics like povidone-iodine/phenol; local anesthetics like lidocaine/benzocaine), pH optimization, preservative efficacy (or self-preservation via high glycerin), stability (light/volatilization sensitivity of iodine), and quality control (viscosity, assay, pH, microbial limits). Safe use hinges on labeling (external use, do not swallow), packaging (amber glass with applicator), and patient-specific considerations (contraindications, pediatric cautions). Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What best describes a monophasic liquid dosage form?
- Single-phase system with solutes molecularly dispersed in a solvent
- Two-phase system with solid suspended in liquid
- Emulsion of oil in water with surfactant
- Aerosolized foam for inhalation
Correct Answer: Single-phase system with solutes molecularly dispersed in a solvent
Q2. What is a throat paint in pharmaceutics?
- Viscous monophasic solution applied to oropharyngeal mucosa using a swab
- Sterile injectable solution for systemic use
- Sugar-based lozenge for sucking
- Pressurized spray for nasal mucosa
Correct Answer: Viscous monophasic solution applied to oropharyngeal mucosa using a swab
Q3. The primary purpose of high viscosity in a throat paint is to:
- Prolong contact time and enhance local drug residence
- Improve sweetness
- Prevent oxidation
- Increase systemic absorption
Correct Answer: Prolong contact time and enhance local drug residence
Q4. The most common base vehicle used in throat paints is:
- Glycerin
- Liquid paraffin
- Mineral oil
- Silicone oil
Correct Answer: Glycerin
Q5. The preferred method of applying a throat paint is:
- Cotton swab/brush
- Oral syringe
- Nebulizer
- Nasogastric tube
Correct Answer: Cotton swab/brush
Q6. Which excipient is commonly used as a mucoadhesive polymer in throat paints?
- Sodium carboxymethyl cellulose
- Talc
- Magnesium stearate
- Starch glycolate
Correct Answer: Sodium carboxymethyl cellulose
Q7. Which of the following is a suitable antiseptic active for a throat paint?
- Povidone-iodine
- Insulin
- Amoxicillin trihydrate
- Omeprazole
Correct Answer: Povidone-iodine
Q8. Why are throat paints classified as monophasic liquids?
- All components are molecularly dispersed with no undissolved solids
- They contain dispersed oil droplets
- They contain suspended solid particles
- They have two immiscible phases
Correct Answer: All components are molecularly dispersed with no undissolved solids
Q9. The best solvent system to dissolve benzocaine for a throat paint is:
- Ethanol–propylene glycol blend
- Purified water alone
- Liquid paraffin
- Castor oil
Correct Answer: Ethanol–propylene glycol blend
Q10. A typical concentration statement for povidone-iodine throat paint is:
- 10% w/v povidone-iodine (≈1% available iodine)
- 0.01% w/v povidone-iodine
- 50% w/v povidone-iodine
- Saturated iodine tincture only
Correct Answer: 10% w/v povidone-iodine (≈1% available iodine)
Q11. A critical stability concern for iodine-containing throat paints is:
- Light and volatilization of iodine
- Freezing
- Carbonation loss
- Photostability improvement with alkali
Correct Answer: Light and volatilization of iodine
Q12. Additional preservative may be unnecessary in a throat paint when:
- When glycerin content exceeds about 60% v/v
- When using purified water only
- When stored at 40°C
- When pH is exactly 7.4
Correct Answer: When glycerin content exceeds about 60% v/v
Q13. Preferred pH range for a lidocaine HCl throat paint is:
- Approximately 5.0–7.0
- Below 2.0
- Above 10.0
- Exactly 9.5
Correct Answer: Approximately 5.0–7.0
Q14. Which quality control test best correlates with mucosal retention time?
- Viscosity measurement at 25°C
- Refractive index
- Melting point
- Boiling point
Correct Answer: Viscosity measurement at 25°C
Q15. Recommended packaging for throat paints is:
- Amber glass bottle with tight closure and applicator
- Clear PET bottle without closure
- Aerosol can with propellant
- Metal tube with crimped end
Correct Answer: Amber glass bottle with tight closure and applicator
Q16. An essential auxiliary label for throat paints is:
- For external use only; do not swallow
- Shake well before use
- For intravenous use
- Store in freezer
Correct Answer: For external use only; do not swallow
Q17. The usual frequency of applying throat paints is:
- 2–4 times daily as directed
- Every 30 minutes
- Once weekly
- Every hour for 24 hours
Correct Answer: 2–4 times daily as directed
Q18. A key contraindication for iodine-containing throat paints is:
- Known hyperthyroidism or iodine sensitivity
- Hypertension
- Lactose intolerance
- Myopia
Correct Answer: Known hyperthyroidism or iodine sensitivity
Q19. A notable adverse effect associated with benzocaine throat paints is:
- Methemoglobinemia in susceptible patients
- Hyperglycemia
- Photosensitivity only
- Nephrolithiasis
Correct Answer: Methemoglobinemia in susceptible patients
Q20. Why should strong sweeteners/flavors be limited in throat paints?
- They encourage swallowing and reduce local contact time
- They increase solubility of all drugs
- They eliminate microbial growth
- They stabilize iodine by complexation
Correct Answer: They encourage swallowing and reduce local contact time
Q21. The correct order of compounding steps for a throat paint is:
- Dissolve actives in suitable solvent, add glycerin/viscosity agents, adjust volume, mix until homogeneous
- Add all powders to bottle and shake with water
- Melt drug, add to paraffin, homogenize
- Triturate with lactose and fill capsules
Correct Answer: Dissolve actives in suitable solvent, add glycerin/viscosity agents, adjust volume, mix until homogeneous
Q22. Why are throat paints often prepared extemporaneously?
- Short shelf life and need for patient-specific actives/strengths
- Lack of licensed pharmacists
- To avoid labeling
- Greater systemic bioavailability
Correct Answer: Short shelf life and need for patient-specific actives/strengths
Q23. The role of a humectant like glycerin in throat paints is to:
- Retain moisture and improve spreadability on mucosa
- Induce effervescence
- Provide sustained systemic release
- Act as propellant
Correct Answer: Retain moisture and improve spreadability on mucosa
Q24. Which local anesthetic form is most appropriate for aqueous throat paints?
- Lidocaine hydrochloride
- Procaine base
- Benzocaine base alone in water
- Bupivacaine base only
Correct Answer: Lidocaine hydrochloride
Q25. A practical strategy to enhance mucoadhesion in a throat paint is to:
- Include 1–2% w/v sodium CMC or carbomer
- Add talc 5%
- Use liquid paraffin base
- Reduce viscosity to near water
Correct Answer: Include 1–2% w/v sodium CMC or carbomer
Q26. The appropriate pharmacopoeial test for microbial quality of throat paints is:
- Microbial limits test as per USP/Ph. Eur. requirements
- Sterility test for parenterals
- Pyrogen test in rabbits
- Endotoxin test
Correct Answer: Microbial limits test as per USP/Ph. Eur. requirements
Q27. What is the pediatric caution for benzocaine-containing throat paints?
- Avoid use in children under 2 years due to methemoglobinemia risk
- Administer freely to neonates
- Safe with no restrictions
- Contraindicated only in elderly
Correct Answer: Avoid use in children under 2 years due to methemoglobinemia risk
Q28. Recommended storage for throat paints is:
- Store below 25°C, protect from light and moisture
- Keep in sunlight to prevent crystallization
- Store in open container
- Freeze before each use
Correct Answer: Store below 25°C, protect from light and moisture
Q29. How does viscosity influence local pharmacokinetics of throat paints?
- Increases residence time, improving local bioavailability without increasing systemic absorption
- Decreases drug stability
- Eliminates first-pass metabolism
- Guarantees zero-order release systemically
Correct Answer: Increases residence time, improving local bioavailability without increasing systemic absorption
Q30. A key difference between a throat paint and a gargle is that:
- Paint is a viscous, locally applied solution for prolonged mucosal contact; gargle is an aqueous rinse expelled after short contact
- Paint is swallowed; gargle is injected
- Paint is always sterile; gargle is not
- Paint contains suspending agent; gargle never contains solvents
Correct Answer: Paint is a viscous, locally applied solution for prolonged mucosal contact; gargle is an aqueous rinse expelled after short contact
