In-Depth Notes on Tablet Coating

Tablet Coating Notes

Introduction to Tablet Coating

  • Definition: Tablet coating is the process of applying a coating material to the surface of a tablet to enhance its properties compared to uncoated tablets.

Objectives of Tablet Coating

  • Prevent Degradation:
    • Light degradation (photolytic)
    • Moisture degradation
  • Masking Characteristics:
    • Masks bitter taste
    • Provides ease of swallowing
  • Identifiable Production:
    • Distinguish different batches through color coding
  • Aesthetic Appeal:
    • Glossy appearance for better marketing
  • Pharmaceutical Clarity:
    • Recognizable shapes and colors for pharmacists
  • Mechanical Strength:
    • Increased strength and protection against cross-contamination
  • Controlled Release:
    • Properties like enteric or controlled release capabilities

Types of Coating Techniques

  • Controlled Release Coating
  • Enteric Coating
  • Film Coating
    • Typical thickness: 20-100 micrometers
    • Process involves spraying a thin polymer film around tablets using conventional pan coaters.
  • Sugar Coating
    • Traditional method using a sucrose solution.
  • Press Coating
  • Functional Coatings

Film Coating Details

  • Formulation Requirements:
    • Polymers: Should be soluble, low viscosity, low permeability (e.g. Hydroxypropyl Methylcellulose, Methacrylate copolymers)
    • Plasticizers: Enhance film strength (e.g. polyethylene glycol, diethyl phthalate)
    • Colorants: Prevent photodegradation, enhance opacity, or provide color (e.g. iron oxide)
    • Solvents: Should be water soluble; organic solvents avoided due to toxicity and costs.

Equipment Used in Film Coating

  • Examples include: Accetacota, Hicoater, Driacoater.
  • Requirements:
    • Atomizing sprayer
    • Proper tablet mixing
    • Sufficient drying air inflow.
  • Ideal Coating Characteristics:
    • Even coverage without abrasive edges.

Sugar Coating Process

  • Involves several stages:
    1. Sealing/Wet Proofing: Moisture barrier using water-insoluble polymers.
    2. Subcoating: Smooth surface application of syrup solution.
    3. Smoothing: Further coating for stability.
    4. Coloring: Ensure recognition and visual appeal.
    5. Polishing: Wax application for glossiness.
    6. Printing: Logos applied mechanically.

Paste Coating and Functional Coatings

  • Press Coating: Compacting granular material around a preformed core.
  • Functional Coatings use for pharmaceutical stability and sustained release.

Coating Composition and Formulation

  • Components:
    • Film Formers: Include both enteric and non-enteric materials (e.g. Hydroxypropyl Methylcellulose)
    • Solvents, Colorants, Plasticizers.
  • Attributes of Ideal Coating Material:
    • Solubility and stability under various conditions, low toxicity, aesthetic properties, resistance to degradation.

Equipment for Coating

  • Conventional Pan Coaters: Standard equipment; effective but requires careful monitoring to avoid volatile solvent issues.
  • Fluidized Bed Coater: Efficient with good mixing and drying capabilities.

Coating Process Parameters

  • Influenced by factors including spray rate, air pressure, temperature, and pan speed.

Defects in Coating

  • Common Issues:
    • Blistering, Cratering, Picking, Pitting, Blooming, and Blushing.
  • Each has specific causes and remedies, often related to formulation conditions, temperature control, and efficiency of drying.

Conclusion

  • Tablet coating is a critical step in pharmaceutical production with various methods and defects requiring careful attention for quality control.

References

  • Industrial pharmacy - Dr. Shalini Sharma。
  • Aulton's pharmaceutics - Michael E. Aulton and Kevin M.G. Taylor。
  • The Theory and practice of Industrial pharmacy - Roop K Khar et al.