The document discusses tablet coating defects and remedies. It begins by introducing tablet coating as the final step in tablet production where a coating is applied to provide benefits like masking taste or protecting the tablet. It then lists and describes 18 common coating defects like blistering, blooming, chipping and provides the likely causes and remedies for each. The defects cover issues with the coating appearance, adhesion, and protection. The document aims to help formulation scientists identify and address coating problems to successfully complete tablet production.

1. Tablet Coating Defects and Remedies
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March 4, 2023
Tablet coating defects and remedies are the crucial concern of a pharmaceutical formulation scientist. The last
critical step in the tablet production cycle is tablet coating after solving problems in core tablet manufacturing.
After finding the tablet coating defects and their remedies, you will successfully complete the tablet production
cycle. So, read this article about tablet coating defects and remedies to identify and solve your coating
problems.
Tablet coating is the application of a coating composition in a moving bed of tablets with the concurrent use of
heated air to facilitate the evaporating of the solvent [1] and with the intention of conferring benefits and
properties to the dosage form over the uncoated variety. Mainly, tablet coating is to be done for masking
unpleasant tastes and odors, protection, identification, improvement of patient compliance, and delivery to the
targeted part of GIT. For a proper coating on tablets, a formulator must know about the following tablet coating
defects and their remedies.
Table of Contents

2. List of tablet coating defects and remedies
1. Blistering
2. Blooming/Dull film
3. Blushing
4. Chipping/ Edge Erosion
5. Cratering
6. Cracking/Splitting
7. Color variation
8. Core Erosion/ Surface Erosion
9. Discoloration
10. Logo Bridging
11. Logo In-filling /Break Lines In-filling
12. Orange Peel (Roughness)
13. Pitting
14. Peeling
15. Sticking and Picking
16. Scuffing of Film-coated Tablets
17. Twinning
18. Tablet Breakage

3. 1. Blistering
It is a coating defect where the film becomes detached from the substrate forming a blister.
Causes and Remedies of Blistering:
Causes Remedies
1. Entrapment of gases or vapor in or under the film due to overheating either
during spraying or at the end of the coating.
Use mild drying
conditions.
2. Effect of temperature on the adhesion, elasticity, and strength of the film.
Use mild drying
conditions.

4. 2. Blooming/Dull film
It is a coating defect where the coating becomes dull immediately or after prolonged storage at high
temperatures. In other words, it is the fading or dulling of a coated tablet color after a prolonged period of
storage at a high temperature.
Causes and Remedies of Blooming:
Causes Remedies
1. High concentration of plasticizer. Use a lower concentration of plasticizer.
2. Low molecular plasticized coating system. Use a high molecular-weight of plasticizer.
3. Blushing

5. It is a coating defect where whitish specks or haziness in the film appear. In other words, it is a haziness or
appearance of white specks in the film-coated tablet.
Causes and Remedies of Blushing
Causes Remedies
1. Precipitation of coating polymer due to use of a poor
solvent or high coating temperature.
Decrease the drying air temperature.
2. Use of sorbitol in coating formulation which causes a major
fall in the thermal gelation temperature of the HPMC
(Hydroxy Propyl Methyl Cellulose), HPC (Hydroxy Propyl
Cellulose), Cellulose ethers, and Methyl Cellulose.
Avoid the use of sorbitol with HPMC
(Hydroxy Propyl Methyl Cellulose), HPC
(Hydroxy Propyl Cellulose), Cellulose
ethers, and Methyl Cellulose.

6. 4. Cratering
It is a coating defect of the film where volcanic-like craters appear on the tablet surface. In other words, it is a
defect in the film’s coating that results in craters appearing on the tablet which in turn results in the exposure
of the tablet’s surface.
Causes and Remedies of Cratering
Causes Remedies
1. Penetration of coating solution at the surface of the tablet, often at the
crown where the surface is more porous causing localized disintegration
of the core.
Decrease the spray rate and
use optimum drying conditions.
2. Inefficient drying.
Use optimum drying
conditions.

7. 3. Application of a higher rate of the coating solution.
Decrease spray application
rate.
4. Low the viscosity of the coating solution.
Increase viscosity of coating
solution.
5. Cracking/Splitting
It is a coating defect in which the film either cracks across the crown of the tablet (cracking) or splits around
the edges of the tablet (Splitting).
Causes and Remedies of Cracking/Splitting
Causes Remedies

8. 1. Higher internal stresses in the film than the tensile
strength of the film.
Adjusting the type and concentration of
plasticizer.
2. High molecular weight polymeric blends or polymers.
Use lower molecular weight polymeric blends
or polymers.
3. Coating and core have different thermal expansion
properties.
Avoid mineral type excipient.
4. Expansion of core due to overheating. Avoid overheating the tablet core.
5. Low mechanical strength of the coating. Use coating with proper mechanical strength.
6. Inadequate coating formulation. Use proper coating formulation.
7. Insufficient plasticization or too much pigmentation. Use adequate plasticizer or pigment.
6. Color variation
It is a coating defect that involves variation in the color of the film. In other words, color variation is a coating
defect where visible differences in color of film are found from tablet to tablet.

9. Causes and Remedies of Color Variation
Causes Remedies
1. Inadequate mixing of tablets. Use geometric mixing.
2. Poor opacity of suspension. Increase the opacity of suspension.
3. Inadequate coating or migration of soluble dyes-
plasticizers and other additives during drying.
Use formulation with various plasticizers and
additives or use optimum drying conditions.
4. Poor spray gun setup. Correct gun setup.
5. Low/high pan load. Load the right quantity of tablets.
6. High core friability. Decrease core friability.

10. 7. Insufficient number of spray guns. Increase the number of spray guns.
8. High coating suspension solid. Reduce suspension solid level.
9. Low hiding power of coating suspension.
Use coating formulation with increased hiding
power.
10. Unequal distribution of coating suspension.
Reduce coating solids to facilitate equal coating
distribution.
11. Insufficient coating suspension applied. Apply a sufficient amount of coating suspension.
7. Chipping/ Edge Erosion: a common tablet coating defect
It is a coating defect where the film becomes chipped or worn away and dented usually at the edges of the
tablet as the coating is being applied.

11. Causes and Remedies of Chipping/ Edge Erosion
Causes Remedies
1.
Pan loading with insufficient amount of
core tablets.
Pan fill with a sufficient amount of core tablets.
2. Inappropriate baffles design. Use appropriate baffles design
3. Low coating film strength. Use high film strength coating formula.
4. Pan speed too fast. Use correct pan speed.
5. Worn tablet punch/tooling. Replace tablet tooling.
6. Sharp edge on tablets. Use proper tablet shape.
7. Low spray rate. Use an optimum spray rate.
8.
High degree of attrition related to the
coating process.
Increase the hardness of the film by increasing the molecular
weight of the coating polymer.
8. Core Erosion/ Surface Erosion

12. It is a coating defect where tablet surfaces erode as tablets tumble during the coating process. Especially this
problem has happened with the presence of inappropriate logo.
Causes and remedies of Core Erosion/ Surface Erosion
Causes Remedies
1. Hygroscopic tablet core.
Reduce the amount of hygroscopic excipient such
as disintegrant.
2. Spray rate is too high or low. Use appropriate spray rate.
3. Pan speed too high. Use the correct pan speed.
4. High friability of core tablet. Use less friable tablets.

13. 5.
Insufficient film strength to provide resistance to
edge damage.
Use high film strength.
6. Poor punch design. Use high quality punch.
7. Punch wear. Use a non-wear punch.
8. Poor logo design or placement. Use proper logo design.
9. Discoloration
It is a rare coating defect where discoloration is appeared either through or on the coating caused by
interactions of ingredients in the core or by heat from the process causing ingredients in the core to migrate
through the coating. The problem is commonly seen with nutraceutical products.

14. Causes and remedies of Discoloration
Causes Remedies
1. Sprayable coating solids are too low. Use film coating formula with higher solids.
2.
Less protection by film from moisture
during storage.
Use a coating formula that provides enough protection
from moisture.
3. Very high spray rate with low temperature.
Decrease spray rate and/or increase processing
temperatures.
4. Low pan speed. Increase pan speed to lessen dwell time.

15. 5.
Migration and melting of ingredients in the
core.
Increase spray rate and/or reduce processing
temperatures.
10. Logo Bridging
It is a coating defect where coating bridges formed across a logo or break line. As more coating is applied to
tablet surfaces, the stresses that develop within the coating as it dries overcome the forces of attachment of
the coating to the tablet surface, causing the coating to pull away within the logo or break line, making either
less visible.
Causes and remedies of Logo Bridging
Causes Remedies
1. Poorly plasticized coating system. Use optimally plasticizer coating.

16. 2. Low adhesion coating system. Use high-adhesion coating.
3. Low adhesion core ingredients. Use high-adhesion core ingredients.
4. Spray rate too high. Reduce spray rate.
5. Product temperature too low. Increase temperature.
6. Poor logo design. Improve logo design.
11. Logo In-filling /Break Lines In-filling
It is a coating defect where the engraved logo or break line is filled with either particle of dried polymer or
solidified foam. Coating droplets are over-dried before contacting the tablet surface, increasing tablet surface
roughness and filling the logo.

17. Causes and Remedies of Infilling
Causes Remedies
1. High atomizing air pressure. Reduce atomizing air pressure.
2. High drying air temperature. Reduce drying air temperature.
3. High-coating suspension solid. Use a low-viscosity coating suspension.
4. Too high gun to bed distance. Optimize gun to bed distance.
5. Poor spray gun design. Use proper spray gun design
6. Turbulent airflow. Minimize pan depression.

18. 7. Aeration of coating suspension.
Use optimized suspension preparation to
avoid aeration.
8. Poor logo design. Improve logo design.
9. Excessive foaming of the coating solution. Improve the mixing process.
10.
Foam and Bubble formation because of air spraying
of a polymer solution.
Add alcohol or use spray nozzle capable of
finer atomization.
11. Over drying of spray. Optimum drying of spray.
12. Orange Peel (Roughness)
It is a coating defect where the surface of the applied film coating is extremely rough and nonglossy, often
taking on the appearance of the skin of an orange.

19. Causes and Remedies of Orange Peel (Roughness)
Causes Remedies
1. Rapid Drying. Use mild drying conditions.
2. Too high coating suspension viscosity. Reduce the viscosity coating suspension.
3. Too low atomizing air pressure. Increase Atomizing air pressure.
4. High spay rate/ Over-wetting. Decrease spray rate.
5. Poor spray gun performance. Use better spray guns.

20. 6. Inadequate distribution of the coating suspension. Decrease in viscosity of coating suspension.
7. Very close gun-to-bed distance. Adjust gun to bed distance.
13. Pitting
It is a coating defect where pits appear on the surface of a tablet core without any visible disruption of the film
coating. In other words, pitting is the deformation of the core of the tablet without any visible signs of
disruption of the film coating.
Causes and Remedies of Pitting
Causes Remedies

21. 1. Inappropriate drying (inlet air) temperature.
Use appropriate drying (inlet
air) temperature.
2.
Melting or dissolution of lubricant on tablet surface or melting of core
ingredient due to high core temperature.
Use control drying
temperatures.
14. Peeling
It is a coating defect where peels off the tablet during or after the coating process. Peeling refers to the
formation of uneven or rough irregularities on the surface of a coating film applied on a core tablet surface.
Causes and Remedies of Peeling

22. Causes Remedies
1. Low adhesion core ingredients. Use high-adhesion core ingredients.
2. Low mechanical strength of the coating.
Use proper composition with improved mechanical
strength.
3. Low adhesion coating system. Use high-adhesion coating.
4.
Coating is rubbing off due to excessive attritional
effects.
Reduce pan speed.
15. Sticking and Picking
It is a coating defect where part of the film of tablets momentarily sticks together or sticks to the pan, often just
after they pass through the spray zone, and then sticked area being detached from the tablet surface.

23. Causes and Remedies of Sticking and Picking
Causes Remedies
1. Inadequate drying. Use optimum drying conditions.
2. High viscosity of coating solution. Increasing viscosity of coating solution.
3. Spray rate is too high. Reduce spray rate.
4. Too low drying air volume Increase air volume.
5. Too low drying air temperature. Increase the inlet air temperature.
6. Pan speed is too low. Increase pan speed.

24. 7. Low atomization pressure. Increase atomization pressure.
8. Poor spray gun setup. Improve spray gun setting.
9. Surface solubility. Increase gun-to-bed distance.
10. High tablet surface porosity. Improve core characteristics.
16. Scuffing of Film-coated Tablets
It is a coating defect in which gray to black marks on the surface of white (or lightly colored) film-coated
tablets appear. Scuffing appears when tablets are more sliding rather than trembling.
Causes and Remedies of Scuffing of Film-coated Tablets

25. Causes Remedies
1.
Larger the tablets and the denser the
core formulation.
Avoid the use of high-density mineral excipients like dicalcium
phosphate, and calcium carbonate.
2.
Elongated shapes or caplet-shaped
tablets.
Use the appropriate tablet shape.
3. Long duration of the coating process. Reduce the coating duration.
4. Pan speed too low. Increase pan speed.
5.
Pan loading with an insufficient
amount of core tablet.
Pan fill with a sufficient amount of core tablets.
17. Twinning
It is a coating defect where tablets stick together especially when two tablets stick together.

26. Causes and Remedies of Twinning
Causes Remedies
1.
Commonly flat surfaces along the edges of capsule-shaped
tablets.
Change tablet shape.
2. Excessively tacky coating formulation.
Use coating formulation which is less
tacky.
3. Inappropriate tablet shape. Use the appropriate tablet shape.
4. Pan speed is too low. Increase pan speed.
5. Spray droplet size is too large. Increase atomizing air pressure.

27. 6. Spray rate too high. Reduce spray rate.
7. Insufficient drying. Use optimum drying conditions.
18. Tablet Breakage
It a defect where tablets break apart during pan loading or while tumbling in the pan or during the coating
process, or during unloading of the coating pan.
Causes and Remedies of Tablet Breakage
Causes Remedies
1. Core tablets are too soft. Change core formulation.

28. 2. Tablets are too brittle. Change core compression parameters.
3. Poor tablet shape for coating. Use the appropriate tablet shape.
4. Poor baffle design. Change baffle design.
5. Too high pan speed. Reduce pan speed.
6. Loading and unloading tablets from the coating pan. Carefully load and unload tablets.
7. Less binder is used in the formula. Use optimum binder quantity.
References
1. Lachman, L., & Liebermann, H. A. (2013). The Theory and Practice of industrial pharmacy. New Delhi:
CBS Publishers & Distributors Pvt. Ltd.
2. Allen, L. V. (2013). Remington: The science and practice of pharmacy. London: Pharmaceutical Press.
3. Aulton, M. E. (2004). Pharmaceutics: The science of dosage form design. Edinburgh: Churchill
Livingstone.
4. Ankit, Gupta & Bilandi, Ajay & Kataria, Mahesh & Neetu, Khatri. (2012). Tablet Coating Techniques:
Concepts and recent trends. IRJP. 3. 50-58.

29. Now, this article titled tablet coating defects and Remedies may help to solve the following questions:
Discuss Coating Troubleshooting.
What are tablet coating defects and remedies?
Discuss some common tablet coating problems and solutions.
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2 thoughts on “Tablet Coating Defects and Remedies”
arshiya
May 22, 2022 at 8:33 AM

30. Pharmaceutical formulation
John White
September 8, 2020 at 1:44 AM
Informative and well-decorated articles regarding tablet coating defects. In your post, your discuss 18
tablet coating defects and their remedies, it is most resourceful that i ever seen in online. Also, I liked
your pictures.
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