Tablet coating defects and remedies are the crucial concerns 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
List of tablet coating defects and remedies
- Blistering
- Blooming/Dull film
- Blushing
- Chipping/ Edge Erosion
- Cratering
- Cracking/Splitting
- Color variation
- Core Erosion/ Surface Erosion
- Discoloration
- Logo Bridging
- Logo In-filling /Break Lines In-filling
- Orange Peel (Roughness)
- Pitting
- Peeling
- Sticking and Picking
- Scuffing of Film-coated Tablets
- Twinning
- Tablet Breakage
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. |
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
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. |
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. |
| 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 |
| 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.
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. |
| 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.
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
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. |
| 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.
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. |
| 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. |
| 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.
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. |
| 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.
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. |
| 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 | |
| 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
| 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.
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. |
| 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
| 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.
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. |
| 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. |
| 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
- Lachman, L., & Liebermann, H. A. (2013). The Theory and Practice of industrial pharmacy. New Delhi: CBS Publishers & Distributors Pvt. Ltd.
- Allen, L. V. (2013). Remington: The science and practice of pharmacy. London: Pharmaceutical Press.
- Aulton, M. E. (2004). Pharmaceutics: The science of dosage form design. Edinburgh: Churchill Livingstone.
- Ankit, Gupta & Bilandi, Ajay & Kataria, Mahesh & Neetu, Khatri. (2012). Tablet Coating Techniques: Concepts and recent trends. IRJP. 3. 50-58.
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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Keywords: Tablet Coating Defects, Finished Tablet Coating Defects, Tablet Coating Defects in Pharmaceuticals, Tablet Coating Defects, List of Tablet Coating Defects, 18 Tablet Coating Defects.
Pharmaceutical formulation
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