Enteric coatings are critical for protecting active ingredients from stomach acid. However, minor formulation errors in these special film coatings can lead to suboptimal drug performance and significant regulatory issues. 

Pharmaceutical manufacturers need to understand these mistakes to avoid costly production delays, regulatory risks, and ensure high-quality products. As tablet coating manufacturers, we have observed seven common errors that occur during the enteric coating process. 

In this blog, we will explain these seven mistakes in the enteric coating process and the proactive steps you can take to avoid them.

Common Mistakes in the Enteric Coating:

The enteric coating process requires precise control over materials and coating process conditions. Common mistakes often involve polymer selection, plasticizer use, coating thickness, and drug compatibility. 

1) API- Polymer Interaction:

APIs can interact physically (adsorption of API onto the polymer or changes in crystallinity) or chemically(hydrolysis or oxidation) with the polymer. For example, polymers with residual acidic groups may destabilise sensitive APIs.

Key risk involved:  Improper drug stability, degradation, or delayed dissolution. It can lead to coating breakdown, film brittleness, cracking, or poor flexibility.

Strategies to avoid this mistake: 

• Understand the chemical nature of both components
• Test interactions early in development and select a polymer based on that
• Use polymer subcoats between the core and the enteric-coated tablet’s layer. 

2) Directly applying an enteric coating to the core: 

When coating formulation is directly applied to the tablet’s core, it may react with the coating material, leading to degradation or poor protection against stomach acid. Some drug cores are acidic or highly water-soluble. When coated directly, they can absorb moisture or cause the coating to fail.

Key risks involved: Uneven coating, delayed dissolution, coating separation or peeling, reduced gastric resistance, and uneven drug release.

Strategies to avoid this mistake: 

• Apply seal coats to create a barrier between the core and the enteric coating
• Choose seal coats based on core properties and drug formulation
• Test core for moisture content, porosity, and surface roughness
• Continuous quality check and visual inspections

3) Uncontrolled Process Parameters

Neglecting to control coating process parameters, such as spray rate, inlet temperature, air velocity, or pan speed during coating, causes defects. For example, too high a spray rate causes clumping and poor film formation, while too low a rate leads to incomplete coverage. 

Key risk involved: Coating defects, such as sticking, uneven coverage, logo bridging, or incomplete film formation.

Strategies to avoid this mistake:

• Maintain rigid controls
• Continuous monitoring throughout the coating cycle
• Fine-tune process variables
• Use a dehumidifier or humidity sensors during coating
• Use Process analytical technology (PAT) tools such as near-infrared (NIR) spectroscopy
• Operators must respond promptly to deviations and document changes

4) Wrong Plasticizer, Pigments, and Opacifiers

Choosing the right plasticizers, pigments, and opacifiers is critical for achieving consistent film performance and drug release. Each ingredient during the coating process must be selected to work well with the enteric polymer and the active pharmaceutical ingredient (API). Compatibility depends on the chemical structure of the plasticizer and the polymer.

Key risk involved: Coating failure, such as brittle, cracked, or uneven coating, can alter the drug’s effectiveness, creating unstable drugs, delay dissolution, alter permeability, flexibility, or cause tackiness

Strategies to avoid this mistake: 

• Test and validate all plasticizers and pigments in the specific polymer system
• Balance pigment type and concentration to maintain both appearance and functional performance
• Optimize opacifier levels 

5) Neglecting moisture sensitivity:

Ignoring the hygroscopic nature of polymers or neglecting product storage conditions leads to hydrolysis, loss of integrity, and accelerated API degradation. 

Key risks involved: Coating breakdown, including tablet softening, coating cracks, API degradation, and drug instability.

Strategies to avoid this mistake: 

• Use desiccant or moisture scavengers
• Apply preocating layers
• Set strict humidity controls
• Optimise drying time and temperature 
• Use polymers with low water permeability
• Use blister packs with moisture barriers 

6) Improper coating application: 

Uniform coating is essential for product quality and consistent drug delivery. Achieving this requires careful attention to tablet coating material, application techniques, process control, and equipment settings. Improper application often leads to coating breakdown.

Key risks involved: Spotty coverage or droplet coalescing leading to inadequate gastric resistance, delayed drug release, and batch variability

Strategies to avoid this mistake:

• Use validated equipment and protocols
• Regularly check spray nozzles and other equipment 
• Proper surface treatments 
• Use automated controls and real-time monitoring
• Frequent sampling during coating 
• Maintain plasticiser levels
• Test different process setups 
• Consistent operator training

7) Ignoring Storage Conditions Post-Coating

Failing to consider the storage requirements of coated products allows exposure to moisture, heat, and light, which can degrade both the tablet coating material and the API. 

Key risks involved: Polymer and API degradation, Tablet coating defects such as swelling or cracking, affecting dissolution. 

Strategies to avoid this mistake:

• Educate on optimal storage conditions
• Ensure proper storage after coating
• Maintain temperature and humidity levels during storage
• Use climate-controlled environments when possible
• Use monitoring devices to prevent unexpected shifts
• Use blister packs with aluminium foil or a bottle with desiccants
• Properly seal the coating 
• During distribution, transport in controlled temperature conditions
• Conduct regular quality testing 

Conclusion:

Avoiding common mistakes in enteric coating formulation is crucial for ensuring drug efficacy and, ultimately, patient safety. By learning from these pitfalls, manufacturers can develop reliable and high-quality products that meet regulatory standards and ensure patient safety.

At Novo Excipients, we offer a wide range of enteric coating formulations. If you have any questions or need further guidance, feel free to reach out to our team of experts at Novo Excipients.

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