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Intro to Tableting Part II | Introduction to Tablet Making Part 2

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31 May 2016 No comments

Tablet Coating

Equipment:

  • Traditional Coating Pan
  • Immersion sword system
  • Pellegrini pan system
  • Immersion tube system
  • Perforated Pan System
  • Driacoated
  • Glatt Coater
  • Hi-Coater
  • Accela Cota
  • Fluidized Bed Coater

Essentials:

  • Speeds of the pan 10-15 RPM (non-aqueous film coat)
  • Pan speed of 3 – 10 RPM (aqueous film coat)

Sugar Coating

Roles:

  • Waterproof/Sealing – helps hardens the tablet and creates a barrier to prevent moisture from seeping in.

Common Sealants:

  • Propylene glycol
  • Shellac (probability of an increase in the disintegration and dissolution due to polymerization and can lead to low bioavailability of the tablet)
  • PEG 4000
  • Zein
  • Cellulose acetate phthalate (CAP)
  • Oleic acid
  • Polyvinylacetate phthalate
  • Dusting Powder/Subcoat
  • Acacia
  • Calcium carbonate
  • Kaolin
  • Cane sugar
  • Dextrose
  • Corn starch
  • Talc
  • Calcium sulfate
  • Smoothing/Syrup Coating - gives color to the tablet as well as refine the subcoated surface
  • Polishing – helps gives the tablet its luster/glossiness.

Ex: Paraffin wax, white beeswax, carnauba wax, naphtha (acts as solvent for the wax)

  • Film Coatings
  • Pan Pour Method – rarely used and has several disadvantages: (a) requires additional steps such as drying to help remove solvents, (b) slow, (c) requires manual operation and (d) aqueous based coatings are not preferred for this method (overwetting of the tablet)
  • Pan Spray Method – it is more preferred than the Pan Pour method due to the automation of the process and increase efficiency.
  • Film Formers
  • Hydroxy Propyl Methyl Cellulose (HPMC) – ideal for pan spray coating system as well as for air suspension due to the solubility features in gastric fluid, aqueous solvent and organic system.

Disadvantage – when the film former is used by itself, it tends to bridge or debossed the tablet surface. HPMC must be mixed with other plasticizers or polymers.

  • Methyl Hydroxy Ethyl Cellulose (MHEC) – it is rarely used as it is soluble/compatible with some organic solvent.
  • Ethyl Cellulose (EC) – EC is combined with other water soluble additives such as HPMC due to its insolubility in water and gastric fluids. Unplasticized EC films tend to be weak and need modifiers in order to obtain the correct formulation.
  • Hydroxy Propyl Cellulose (HPC) – HPC is soluble in below 40 C water but insoluble above the 45C. Is also soluble to other polar organic solvents and gastric fluids.
  • Povidone – the average molecular weight is 10k, 40k and 160k, 360k; K-30 is the most commonly used in coating and binding tablets; 4 viscosity grade (K-15, K-30, K-60, K-90)
  • Polyethylene glycols (PEG) – the (200-600) low molecular weights PEG is liquid when at room temperature and are often used as plasticizer. (900-8000) high molecular weights PEG on the other hand are in white and waxy solid form when in room temperature. The combination of the PEG waxes with the CAP gives the films its solubility.
  • Acrylate polymers – this is marketed under Eudragit. Eudragit E is a co-polymer cationic that is based on Poly (methyl) acrylates. The Eudagit E swells when exposed to gastric fluid of up to 5pH. It is also freely soluble. The polymers produces films that delays action. The Eudragit RL and RS have low quaternary ammonium content and are co-polymers.

Enteric Materials

Ideal Enteric Polymer – above pH 5 or soluble at pH5

  • Cellulose acetate phthalate (CAP) – most commonly used. Tablet is soluble at above pH 6
  • Aquateric – patented aqueous dispersion of CAP (marketed by FMC Corp. USA); particle size in aquateric .05 – 3 micron (CAP)
  • Acrylate polymers
  • Hydroxypropyl methylcellulose phthalate - Common brand names: HP-50, HP-55, HP-55-S. It is soluble at below PH (5 to 5.5) than other polymers.

Solvents – used to dissolve polymers where water is the ideal solvent.

Plasticizers – it is used to alter the polymer’s physical characteristics. It also optimizes the tensile strength, flexibility, adhesion properties of films and also modifies the polymer-polymer interaction.

Commonly Used Plasticizer:

  • Castor oil
  • Surfactants
  • Propylene Glycol (PG)
  • Lower molecular weight (200-400 series) PEG
  • Glycerin

PEG and PG uses aqueous coating whereas castor oil and spans used for organic solvent coating solution.

Colorants

Often in tablet mixes (pill mixes) a colorant is added to help identify the final product.

Concentration: (light shade)-0.01%

- (dark shade) 2%

Commonly Used:

  • Lakes (most preferred)
  • Anthocyanins
  • Iron oxides
  • Carotenoids
  • Caramel
  • Flavones
  • Chlorophyll
  • Carminic acid
  • Turmeric

Other Coloring Agents that do not need milling devices:

  • Sugar coating - Opalux
  • Film coating – (concentrate) - Opadry
  • Film coating – Opaspray

Opaquant Extenders

These extenders helps increase the film coverage of the color resulting to reduce cost of expensive colorants.

Example of Opaquant Extenders:

  • Aluminum hydroxide
  • Aluminum oxide
  • Calcium sulfate
  • Magnesium oxide
  • Talc
  • Titanium dioxide (commonly used)

Film Defects

  • Sticking/picking – happens when there are some areas of the film that are pulled away from the tablets surface. It may also be due to the tablet sticking together or when overwetting occurs then the tablet will stick to the pan causing the tablet’s core to be exposed.

Prevention - (i) reduce the application times of the coating solution and (ii) increases the inlet air temperature.

  • Roughness – this defect happens when the polymer to be applied dries before reaching the coating pan’s base.

Prevention – (i) to move the atomizer deeper into the coating pan and (ii) decrease the atomization

  • Orange peel effect – this surface defects leads to the tablet to appear non-glossy or rough and appear to look like an orange.

Prevention – (i) adds additional solvent to help reduce the solution’s viscosity level and (ii) use mild drying condition.

  • Bridging & Filling – happens when the film pulls away from the tablets bisect area.

Prevention – change the plasticizer used or increase the concentration

  • Blistering – this occurs when there is fast and rapid drying of the solvent.

Prevention – to use mild and drying condition

  • Hazing – the tablet’s coating becomes dull after a long period of being stored at high temperature.

Prevention – (i) to increase the plasticizer’s molecular weight and (ii) to reduce the concentration of the plasticizer.

  • Color Variation – this is a defect that results to the tablets having different color.

Prevention – (i) medium drying condition (ii) reformulate the plasticizer or additives used (iii) proper mixing

  • Cracking – this is when the film cracks around the tablet’s crown or split around the edges.

Prevention – adjust the concentration and type of plasticizer used.