Film coating on tablets is a crucial step in the manufacturing process of tablets. However, being in business for decades, we have encountered common challenges that every tablet manufacturer faces. We have outlined these challenges and suggested ways to overcome them.

This blog is a single sheet for each tablet coating challenge related to pharmaceutical excipients.

Excipient-Driven Challenges in Tablet Coating and How to Fix Them?

While coated tablets have their advantages, they also exhibit a fair share of defects, primarily cosmetic defects. Many of these issues occur due to improper excipient function in tablets.

These tablets may or may not affect the efficacy of the tablets. However, the perception of the products will affect consumer confidence in your tablets, which in turn will impact your overall sales. 

Most of these problems can be avoided with a scientific and proactive approach. 

1. Sticking  or Picking

Film coating on tablets adheres to the packet or other tablets during the coating process. This causes uneven surfaces and damaged tablets.

Causes: 

• Certain binders are hygroscopic, meaning they absorb moisture. Because of excess moisture, the tablets may become sticky.
• High sugar content in the specific coating can worsen sticking.

Solutions:

• Replace hygroscopic pharmaceutical excipients
• Balance hygroscopic coating with anti-tacking agents or hydrophobic excipients

2. Cracking, Chipping, or Peeling of the Coating

The film coating on tablets breaks, chips off, or peels away from the tablet surface. This leads to dose loss and inconsistent drug release.

Causes:

• Inadequate plasticizers
• Weak fillers or disintegrants

Solutions: 

• Adjust plasticizer type and concentration.
• Choose stronger fillers and reinforce core integrity
• Maintain uniform and optimal coating thickness

3. Poor Film Adhesion

The coating does not bond well to the tablet core and flakes off easily. This can expose the tablet to moisture or change its taste.

Causes:

Waxy lubricants or excessive use of glidants can make the tablet surface too smooth.

Solutions:

• Modify the formulations and add a seal coat 
• Avoid overuse of glidants and hydrophobic lubricants 
• Use a hydrophilic polymer to maintain a better coat grip
• Use low-viscosity polymers

4. Color Variation

The coating color appears uneven or patchy across tablets in the same batch. This makes tablets look unprofessional and can confuse patients.

Causes:

• Uneven distribution of pigments 
• Opacifiers with poor wetting properties

Solutions:

• Add suspending agents to maintain homogeneity
• Use pre-mix for even coating

5. Blooming

A hazy or whitish layer forms on the surface of the coated tablet over time. This happens when plasticizers migrate to the surface and crystallize.

Causes: 

• Too many plasticizers 
• Using a plasticizer with a low molecular weight

Solutions:

• Decrease the concentration of plasticizers
• Increase the molecular weight of the plasticizers

6. Over-wetting and Erosion

Tablets become too wet during coating and start to erode or dissolve slightly. This can alter the tablet’s shape and compromise its structural integrity.

Causes:

• Highly water-soluble excipients dissolve on contact with aqueous coating
• Low binder content

Solutions:

• Use low-solubility diluents
• Add a binder with higher strength
• Use water-resistant seal coats

7. Core Deformation or Breakage

The tablet core deforms, cracks, or breaks apart during the coating process. This makes tablets unusable and can cause dosing errors.

Causes:

• Low binder
• The wrong type of disintegrant.
• Inadequate compaction during tablet manufacturing

Solutions:

• Use stronger binders
• Design a core that can withstand stress during coating.

8. Orange Peel (Roughness)

The coating surface appears bumpy and rough, resembling the texture of orange skin. This is caused by poor levelling of the coating droplets.

Causes: 

• Excess fillers, binders, or poorly soluble excipients
• Insufficient plasticizer
• Weak binders or fillers

Solutions:

• Add wetting/dispersing agents
• Use adequate plasticizers
• Use better mixers
• Use a stronger binder or seal coat

9. Capping or Lamination

The tablet splits into layers, or the top/bottom cap separates during compression. This is due to weak binding inside the core.

Causes:

• Excessive moisture
• Uneven bonding of incompatible excipients
• Elastic recovery of excipients 

Solutions:

• Use pre-gelatinized fillers
• Blend with less elastic excipients 
• Check excipient compatibility early 
• Match binder to filler 

Besides these, there are additional tablet coating defects that are not directly caused by pharmaceutical excipients but rather by a flawed tablet coating system.

 Additional Common Tablet Coating Defects

• Cratering:  Craters appear on the tablet due to insufficient drying time.
  
• Pitting: When the core becomes hotter than the melting point of the materials used, the core often deforms.
• Blushing: Appearance of white specks due to excessive coating temperature or use of gelatin.
  
• Infilling: Distinctive symbols formed on the tablet due to the improper dispersion of polymer solution.
  
• Blistering: Film detaches from the tablet substrate due to high-temperature drying.
  
• Capping or Lamination: This can also happen due to trapped air or high compression speed. 

Simple recommendations to avoid tablet coating challenges:

• Choose the proper excipients that are compatible with each other
• Optimize Core Preparation
• Sieve and blend powdered excipients
• Use a Seal coat whenever needed 
• Balance suspensions and solids
• Perform batch trials first
• Inspect regularly during the manufacturing process 

Besides these, for a defect-free coating, it is recommended to optimize tablet coating systems. You can do this by training operators and encouraging them to record anomalies. 

Conclusion:

The function of excipients in tablets is often underestimated. However, they play a significant role in tablet coating quality. If you use the wrong binders, plasticizers, or fillers, you’ll see issues such as sticking, cracking, or uneven color. By choosing the right ingredients and fine-tuning your coating mix, you can avoid these defects. 

Ready to improve your tablet coating? Contact us today for tailored coating solutions. At Novo Excipients, a pharmaceutical excipients manufacturers, we also provide pre-mix coating to avoid defects in tablet coating. 

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