Tablet Coating Processes Quiz

Tablet Coating

• Tablet coating is adapted from food preservation processes.
• Dr. Dale Wurster created the first air suspension coater in 1950.
• Wurster introduced airflow and perforated coating pans to the tablet coating machine.
• Wurster's work led to the first reproducible and uniform tablet coating.

Tablet Coating Principles

• Tablet coating increases cost.
• Coating a tablet is often done for the following reasons:
  • To mask undesirable taste, odor, or color of the drug.
  • To provide physical and chemical protection for the drug.
  • To control drug release from the tablet.
  • To protect the drug from stomach acidity with an enteric coating.
  • To improve the aesthetic appeal through color and contrasting printing.
  • To aid tablet movement and swallowing, especially for patients with dysphagia.

Tablet Coating Process

• The tablet coating process considers substrate, process & equipment, coating formulation, and coating quality.

Tablet Coating: Three Main Parts

• Tablet Properties:
  • Ideal tablet shape for coating
  • Tablet physical properties (e.g., strength, intactness, and absence of imperfections)
  • Tablet surface characteristics (e.g., texture for coating processes)
• Coating Compositions:
  • Non-enteric coating materials.
  • Enteric coating materials.
  • Solvents.
  • Plasticizers.
  • Colorants.
  • Opaquants.
• Coating Process:
  • Coating equipment
  • Coating process details (e.g., spraying, ladling, etc.)
  • Evaluation of film and film defects

Preferred Tablet Properties for Coating

• Tablets must withstand mechanical stress during the process.
• Tablet shapes should be intact and free of imperfections.
• Brittle tablet surfaces may soften with heat or be affected by coating materials.

Preferred Tablet Properties for Coating

• The physical shape of the tablet is important.
• Coating materials create a tacky, semisolid, and eventually nontacky surface on the tablet.
• Constant movement of tablets within the machine prevents sticking together.
• The ideal tablet shape is a sphere to facilitate smooth rotation.
• Square flat-faced tablets tend to have problems due to build-up of coating materials on the surfaces.

Tablet Surface Hydrophobicity/Hydrophilicity

• The surface characteristics of the tablet should match those of the coating material.
• Surfactants may be added to the coating solution to help the coating materials wet the tablet.

Coating Compositions

• Coating materials can be deposited physically (e.g., sugar, wax coatings).
• Coating materials need to be soluble in the coating preparation solvent.
• Coating materials should produce elegant-looking products.
• Film properties should not change significantly with aging (stability).
• Coating materials should be essentially tasteless, odorless, and colorless.
• Coating materials should be compatible with common coating solution additives.
• Coating materials should not bridge or fill tablet surface imperfections.
• Coating materials should be resistant to cracking.

Coating Compositions: Film-Forming Materials

• Polymers create the film around the tablet.
  • Can be classified as non-enteric or enteric.
• Non-enteric Materials: Tend to dissolve in the GI tract and release the drug.
  • Examples Include Hydroxypropyl methylcellulose (HPMC) and Ethyl Cellulose (EC).
• Enteric Materials: Dissolve based on the pH of the GI tract.
  • Examples Include Hydroxypropyl methyl cellulose phthalate (HPMCP), Cellulose Acetate Phthalate, and Acrylate Polymers.

Non-enteric Materials (Non Functional FC)

• Hydroxypropyl methylcellulose (HPMC) is available in different viscosity grades.
• It is often the material of choice for air suspension and pan-spray coating systems.
• HPMC is close to ideal for film coating because of its solubility, non-interference with tablet disintegration, flexibility, and stability in the presence of heat, light, moisture, and air. It can also easily incorporate color and additives.
• HPMC tends to bridge and fill debossed tablet surfaces when used alone.

Enteric Materials and Characteristics

• Key reasons for enteric coating include protecting the drug or stomach from enzymes and certain antibiotics, protecting the stomach from drugs (e.g., salicylates), delivering drugs optimally absorbed in the small intestine and providing a delayed-release component.
• Ideal enteric coating materials have resistance to gastric fluids, ready permeability to intestinal fluids, compatibility with drug substrates, stability in coating solutions, a continuous uninterrupted film, and must be non-toxic.

Challenges for Enteric Coated Tablets

• Passing the USP disintegration test doesn't guarantee bioavailability.
• The pH of the stomach varies between individuals, and from one time to another. Some patients may have achlorhydria or hypochlorhydria.
• The amount of gastric fluids varies between individuals and over time.
• Enteric coating techniques sometimes involve the use of retardant polymers that may struggle with rapid solubility in the GI tract.

Coating Compositions: Solvents

• Water, ethanol, chloroform, and acetone are commonly used. Water is preferred due to environmental and economic considerations.

Coating Compositions: Plasticizers

• Plasticizers are non-volatile materials added to films to improve flexibility and adhesion.
• Correct proportions of plasticizers add flexibility to the polymer by decreasing molecular rigidity.
• A combination of plasticizers may be needed for specific effects.
• Concentration of plasticizer depends on factors such as polymer type, application method, and manufacturer recommendations.
• Common examples include castor oil, glycerin, low molecular weight polyethylene glycol (PEG), Tweens, and Spans.
• PEG is typically used for aqueous coatings whereas other plasticizers like castor oil and Spans are commonly used in organic coating solutions.

Coating Compositions: Colorants

• Colorants may be soluble in the solvent or be insoluble powders.
• Lakes pigments are the preferred choice for sugar or film coating systems due to their consistent reproducibility in color distribution.

Coating Compositions: Opaquants

• Fine inorganic powders used to increase film coverage, providing a white coating or masking the tablet core's color.
• Colorants are more expensive than opaquants with less colorant needed.
• Titanium dioxide is a common opaquant.

Coating Process

• Tablet coating involves applying coating materials to moving tablets while using heated air to evaporate the solvent.
• Coating materials are distributed by moving the tablets in a coating pan.
• Tablets pass through an application zone to receive coating materials.
• The tablets are recycled in the application zone until the desired thickness is reached.

Coating Equipment

• 1- Conventional Pan System:
  • Consists of a spherical pan mounted on a stand.
  • Pan is rotated by a motor.
  • Heated air is directed into the tablet bed, which is exhausted through ducts.
  • Coating materials are applied to the tablets by ladling or spraying.
  • Spraying is preferred due to speed, even distribution, and reduced drying time
• 2- Perforated Pan System:
  • Consists of a perforated drum rotating in a closed chamber.
  • Drying air is passed through the tablets and exhausted through perforations.
  • Efficient for high coatings and can be automated for sugar and film coating.

Types of Coating and Processing

• Sugar Coating:
  • Used in the past but may still have value for aesthetics.
  • Involves coating steps such as sealing, sub-coating, syruping, finishing, and polishing.
    • Seal coating prevents moisture, and subsequent coatings are applied until desired thickness.
    • Shellac and Zein are seal coating agents.
    • Various steps build up the desired tablet size, edges and color.

Film Coating Process

• Film coating is faster and more economical than sugar coating.
• Utilizes film forming polymers with various properties.
• Final tablet weight is only slightly increased (2-5%).
• Film coating utilizes the same equipment and methods as sugar coating.

Pan Spray Method

• Introduction of spraying equipment was an important evolution in film coating.
• Spraying allows automatic control of liquid application during film coating.

Pan Spray Method: Control Variables

• Pan shape, load, and rotational speed affect the mixing of tablets
• Speed must be appropriate to prevent either localized overwetting or inefficient drying.
• Proper control of temperature, volume, and rate are key considerations in the process air when drying coated tablets.

Evaluation of Coated Tablets

• General appearance (e.g., color, continuity).
• Physical defects.
• Performance (e.g., drug release, long-term stability.
• Visual inspection is often sufficient to assess quality.
• Rubbing on paper can indicate coat strength.

Film Defects

• Sticking and picking (due to tackiness and overwetting)
• Roughness (due to some droplets drying too rapidly).
• Orange peel effect (due to poor spreading).
• Bridging and filling (due to lack of plasticizers).
• Blistering (due to uneven drying conditions).

Test your knowledge on the various processes and purposes of tablet coating in pharmaceutical formulations. Learn about sealing coats, subcoating steps, and the benefits of enteric coatings. This quiz covers essential aspects of drug release control and coating challenges.