L53 Tablet Coating and Drug Release

• Tablet coating


  Application of a coating material to exterior of a tablet to confer beneficial properties as compared to the uncoated form
• Tablet coating technology


  • Applicable to multi-particulate systems intended for modified/controlled release applications
• Three main types of coatings

  • Film coating
  • Sugar coating
  • Press coating
• Sugar coating


  1. Sealing of tablet core to prevent entry of water (usually shellac or cellulose acetate phthalate)

  2. Sub-coating to create a rounded profile via the addition of calcium carbonate or talc in a sucrose solution

  3. Smoothing, which requires application of sucrose syrup

  4. Colouring, used with almost all sugar coated tablets

  5. Polishing with beeswax and carnauba wax to create a high gloss surface finish

  6. Printing identifies a manufacturer's logo or code
• Film coating


  1. Deposition, usually by spraying, of a thin film of polymer surrounding the tablet core

  2. Coating liquid (a solution or suspension) contains a polymer in a suitable liquid together with other ingredients, such as pigments and plasticizers
• Tablet coating


  1. Solution is sprayed onto a rotating, mixed tablet bed or fluid bed

  2. Drying conditions permit solvent removal to leave a thin deposition of coating material around each tablet core
• Coating problems


  • Picking/chipping
  • Roughness
  • Sticking
  • Film cracking/peeling
• Enteric Coating


  Protects the tablet core from disintegration in the acid environment of the stomach for one or more of the following reasons: Prevention of acid attack on a drug that is unstable at low pH, Protect the stomach from the irritant effect of certain drugs, Facilitate absorption of a drug that is preferentially absorbed further down the GI tract (e.g., colon), Taste masking
• Ideal enteric coating polymers


  • Insoluble in aqueous media at low pH but, with increasing pH, then experience an abrupt, well-defined increase in solubility at a specific pH
• Enteric coating


  1. Possible using both sugar and film-coating

  2. Enteric polymers for direct film-coating: cellulose acetate phthalate (CAP), polyvinyl acetate phthalate (PVAP), or a suitable acrylic derivative

  3. Sealing coat is modified to comprise an enteric polymer during sugar-coating

  4. Sufficient weight of enteric polymer required to ensure an efficient effect; typically 2 or 3 times that required for simple film coating
• Delayed release tablet


  • Drug core coated with delayed release membrane (dry)
  • Exposure to pH of the small intestine (pH 6.8) dissolves the coating, which is resistant to acidic conditions in the stomach
  • Exposed drug-loaded core disintegrates, drug dissolves and is released
• Enteric coating polymers


  • Cellulose acetate phthalate
  • Acrylates: methacrylic acid - ethyl acrylate (1:1) copolymer
  • Polyvinyl acetate phthalate
• Enteric coating polymers


  • Have free carboxylic acids groups
  • Insoluble at low pH
  • Sharp increase in solubility at specific pH; e.g., cellulose acetate phthalate at pH 5.2
• Typical enteric coating composition

  • Cellulose acetate phthalate (CAP) 5.0% w/w
  • Glyceryl triacetate 1.0% w/w
  • Isopropyl alcohol 17.0% w/w
  • Dichloromethane 68.5% w/w
  • Water 8.5% w/w
• Multi-particulates

  • Commonly 'pellets' or 'beads' - provide opportunities for the design of new controlled and delayed release oral formulations
  • Drug dose is divided into 1000s of spherical particles of diameter 0.5 - 2.0 mm
  • Particles can either be filled into a sachet, encapsulated or compressed into a tablet
  • Primarily used for controlled-release medicines having gastro-resistant or extended release properties, or for site-specific drug delivery
• Advantages of multi-particulates


  • More consistent GI transit than single dose monolithic tablet
  • Less likely to suffer from dose dumping
• Disadvantages of multi-particulates


  • Control of membrane characteristics using film-coating can be difficult
  • Multi-particulates are difficult to retain in the upper GI tract
• Properties of multi-particulates


  • Good stability, good flow properties, high bulk density, very low hygroscopicity, and are easy to dose
• Types of multiparticulates

  • Extruded/spheronized granulates
• Production of extruded/spheronized granulates

  1. Produced in modified granulating equipment

  2. Drug granulate extruded through (e.g.) a mesh under pressure to form small particles for spheronization
• Drug release mechanisms from multiparticulates

  • Diffusion
  • Osmosis
  • Erosion
• It is recommended that you take your Losec omeprazole capsules in the morning
• You can take your Losec omeprazole capsules with food or on an empty stomach
• Swallow your Losec omeprazole capsules whole with half a glass of water. Do not chew or crush the capsules. This is because the capsules contain coated pellets which stop the medicine from being broken down by the acid in your stomach. It is important not to damage the pellets
• It is not a good idea to take enteric-coated tablets/capsules with an antacid. This would cause pH of gastric fluid to increase such that the coat might dissolve in the stomach
• Multiple-unit pellet systems (MUPS)


  • Enteric-coated particles compressed into a tablet
  • The polymer coat must be more flexible because of compression forces that are applied in the tableting process
  • Methacrylic acid copolymers appear best suited to enteric coating the particles that make up MUPS tablets
  • MUPS tablets work on the same principle as enteric-coated granules in a capsule - tablet disintegrates in stomach and small particles pass through the pyloric sphincter
• MUPS tablets may be broken and dispersed, as long as particles within are not chewed or crushed