“Understanding Common Film Coating Defects in Pharmaceutical Manufacturing”

Film coating of tablets serves multiple purposes, including improving stability, controlling release, taste masking, and enhancing appearance. However, variations in processing conditions can lead to defects that impact the quality of the tablets produced. Recognizing these defects and their causes can significantly help reduce film defects.

Common Film Coating Defects

• Twinning:
  Twinning occurs when tablets stick together, usually associated with flat-faced tablets.
  –Causes: Overwetting and tablet shape.
  -Remedy: Slight curvature on the tablet surface can reduce the problem, and avoiding over-wetting of the tablet core is essential.
• Color Variation:
  Uneven color on the surface of film-coated tablets.
  – Causes: Improper mixing, variation in spray pattern and speed of the coating pan, insufficient coating, and migration of dyes and plasticizers during drying.
  – Remedy: The use of lake dyes and ensuring a uniform spray pattern can mitigate this issue.
• Dull Film:
  A lack of glossy appearance and a rough surface on film-coated tablets.
  – Causes: Improper drying, incorrect formulation, and problems with the coating equipment. High processing temperatures can also contribute.
  -Remedy: This problem often occurs with cellulosic polymers. Proper formulation and optimization of processing temperatures can overcome this defect.
• Blistering:
  Formation of small bubbles or blisters on the tablet surface, impacting quality.
• Causes: Rapid evaporation of solvent from the tablet core due to temperature variations differential expansion and contraction of tablet core and film coating, moisture contamination, and high coating thickness.
•  Remedy: Optimizing drying conditions is crucial to prevent blistering.
• Cracking:
  Development of small fractures on film-coated tablets.
  – Causes: Lower tensile strength of the film and differences in thermal expansion coefficients between the tablet core and the coating, leading to shrinkage and cracking.
• Using high molecular weight polymers can increase film tensile strength while adjusting internal stresses with plasticizers can help.

  Sticking and Picking: Sticking and picking means the adhesion of tablets either to each other or the coating pan takes place.

  • Cause: Insufficient drying, and excess moisture in the coating solution.
  • Remedy: Optimum drying conditions and reducing moisture content in the coating solution, prevent sticking and picking.
• Some other defects include bridging and filling, surface roughness, etc.