Introduction: Understanding defects in tablet coating is essential for B. Pharm students focused on formulation and quality control. Tablet coating defects—such as peeling, blistering, orange peel, cracking, mottling, and picking—affect drug appearance, stability, and patient acceptability. Learning the root causes (formulation, process, equipment, and environmental factors) and prevention strategies (optimizing binder, plasticizer, solvent system, spray parameters, and curing) builds practical troubleshooting skills. This topic emphasizes film coating and sugar coating mechanisms, critical process parameters, and analytical checks to minimize defects and ensure consistent tablet performance. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which coating defect is characterized by localized loss of coating exposing the tablet core due to poor adhesion?
- Orange peel
- Picking
- Cracking
- Blistering
Correct Answer: Picking
Q2. A rough, textured surface resembling citrus skin on a tablet coating is called:
- Bridging
- Orange peel
- Mottling
- Crawling
Correct Answer: Orange peel
Q3. Which factor most commonly causes blistering during film coating?
- Low inlet air temperature
- High tablet porosity with trapped moisture
- Excessive plasticizer
- Low spray rate
Correct Answer: High tablet porosity with trapped moisture
Q4. Mottling in coated tablets is primarily related to:
- Inadequate drying time only
- Uneven pigment or dye distribution in coating solution
- Excessive pan speed
- Wrong tablet press tooling
Correct Answer: Uneven pigment or dye distribution in coating solution
Q5. Which coating polymer is water-soluble and commonly used for immediate-release film coatings?
- Ethylcellulose
- Eudragit RS
- Hydroxypropyl methylcellulose (HPMC)
- Cellulose acetate phthalate
Correct Answer: Hydroxypropyl methylcellulose (HPMC)
Q6. Crawling or crawling-like defects are usually caused by:
- Excessive plasticizer concentration
- Poor surface wetting due to low binder or high surface tension
- Overcuring at high temperature
- Use of a solvent-free system
Correct Answer: Poor surface wetting due to low binder or high surface tension
Q7. Which parameter should be reduced to prevent spray-drum accumulation and tablet erosion?
- Atomization air pressure
- Coating solution solids content
- Spray rate
- Plasticizer type
Correct Answer: Spray rate
Q8. Which plasticizer function helps avoid cracking and improve film flexibility?
- Increase polymer crystallinity
- Reduce polymer glass transition temperature (Tg)
- Increase solvent evaporation rate
- Promote pigment aggregation
Correct Answer: Reduce polymer glass transition temperature (Tg)
Q9. Twinning (sticking of tablets together) during coating is most likely caused by:
- Low tablet hardness only
- High tackiness of wet coating and insufficient drying
- Excessive coating weight gain only
- Use of nonpolar solvents
Correct Answer: High tackiness of wet coating and insufficient drying
Q10. Which measure best reduces mottling caused by API migration to the coat surface?
- Increase inlet air temperature substantially
- Use a sub-coating/seal coat to isolate the core
- Eliminate plasticizer from the formulation
- Reduce tablet weight
Correct Answer: Use a sub-coating/seal coat to isolate the core
Q11. In aqueous film coating, a too-high atomization air pressure typically leads to:
- Large droplet size and poor coating distribution
- Very fine droplets increasing overspray and drift
- Immediate curing of the film
- Reduced evaporation of solvent
Correct Answer: Very fine droplets increasing overspray and drift
Q12. Which solvent system is preferred for moisture-sensitive cores to minimize core uptake?
- Pure aqueous system
- High-boiling water-miscible solvents
- Organic solvent or organic–aqueous co-solvent with fast drying
- Glycerin-based solvent
Correct Answer: Organic solvent or organic–aqueous co-solvent with fast drying
Q13. What is the primary purpose of curing after film coating?
- To remove pigments
- To allow polymer chain relaxation and coalescence, improving film mechanical properties
- To increase coating viscosity
- To harden the tablet core
Correct Answer: To allow polymer chain relaxation and coalescence, improving film mechanical properties
Q14. Which defect is characterized by long troughs over tablet edges where coating fails to fill depressions?
- Bridging
- Edge effect
- Peeling
- Mottling
Correct Answer: Edge effect
Q15. Bridging occurs when coating accumulates in tablet concave areas; a preventive strategy is:
- Increase solids loading dramatically
- Use coarser spray droplets and slower spray rate
- Reduce pan speed to zero
- Omit plasticizer
Correct Answer: Use coarser spray droplets and slower spray rate
Q16. Which analytical QC test specifically assesses coating uniformity and thickness?
- Dissolution testing
- Friability test
- Cross-sectional microscopy or tablet film thickness measurement
- Loss on drying of core
Correct Answer: Cross-sectional microscopy or tablet film thickness measurement
Q17. Excessive sheen, tackiness, and poor gloss after coating often indicate:
- Under-plasticization
- Over-plasticization or insufficient drying/curing
- Correct polymer selection
- Excessive pigment dispersion
Correct Answer: Over-plasticization or insufficient drying/curing
Q18. Which coating material is typically used to achieve sustained-release by forming water-insoluble films?
- Polyethylene glycol (PEG)
- Hydroxypropyl methylcellulose (HPMC)
- Ethylcellulose
- Sucrose
Correct Answer: Ethylcellulose
Q19. A sudden increase in tablet surface temperature during coating is most likely to cause:
- Improved pigment dispersion
- Over-drying of the film and cracking
- Better adhesion and elimination of picking
- Reduced solvent evaporation
Correct Answer: Over-drying of the film and cracking
Q20. In sugar coating, which step provides the smooth rounded shape and initial sealing of the core?
- Polishing
- Sealing (sub-coating)
- Color glazing
- Final syruping
Correct Answer: Sealing (sub-coating)
Q21. Which property of the coating suspension most directly affects spray droplet formation and atomization?
- pH only
- Viscosity and surface tension
- Tablet core hardness
- Tablet die fill
Correct Answer: Viscosity and surface tension
Q22. Which additive is commonly included to improve pigment wetting and prevent pigment settling in the coating dispersion?
- Anti-tacking agent
- Surfactant or dispersant
- Filler like talc
- Lubricant like magnesium stearate
Correct Answer: Surfactant or dispersant
Q23. Which of the following is an indicator of inadequate film coalescence?
- Uniform glossy surface
- Sticky or powdery film that rubs off
- High mechanical strength of the film
- Homogeneous color
Correct Answer: Sticky or powdery film that rubs off
Q24. Which environmental condition in the coating room can exacerbate sticking and picking?
- Low relative humidity
- High relative humidity
- Low temperature with low humidity
- Constant laminar airflow
Correct Answer: High relative humidity
Q25. What is the typical effect of increasing pan speed during film coating?
- Longer residence time and thicker layers per pass
- Reduced tablet movement and potential for uneven coating
- Faster drying due to increased tumbling and exposure
- Decreased risk of chipping at rim only
Correct Answer: Faster drying due to increased tumbling and exposure
Q26. Which defect results from excessive solvent evaporation at spray impact, producing a rough or coarse film?
- Blooming
- Skinning
- Orange peel
- Peeling
Correct Answer: Orange peel
Q27. Which test helps determine whether a film coating will withstand mechanical stress during handling?
- Dissolution in water
- Friability testing of coated tablets
- Loss on drying of coating solution
- pH stability test of API
Correct Answer: Friability testing of coated tablets
Q28. Which practice reduces the likelihood of color bleeding during aqueous coating?
- Use of highly water-soluble dyes without binders
- Incorporation of insoluble lake pigments or use of binders and seal coats
- Increasing tablet core moisture
- Applying coating at very low temperature
Correct Answer: Incorporation of insoluble lake pigments or use of binders and seal coats
Q29. Which of the following is a sign of overapplication of coating weight?
- Improved dissolution always
- Bridging, excessive gloss, and increased disintegration time
- Reduced friability with no other effects
- Immediate elimination of mottling
Correct Answer: Bridging, excessive gloss, and increased disintegration time
Q30. To troubleshoot persistent picking, which sequence of actions is most appropriate?
- Increase pigment concentration → increase spray rate → increase relative humidity
- Reduce spray rate → increase inlet air temperature moderately → increase plasticizer or binder concentration
- Stop drying → add more talc to coating mix → reduce atomization pressure
- Switch to a solvent-free coating instantly → decrease pan speed drastically → remove plasticizer
Correct Answer: Reduce spray rate → increase inlet air temperature moderately → increase plasticizer or binder concentration
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.
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