Film Coating Process of Tablets in Pharma Manufacturing

Film Coating

• Minimal weight gain (2-3% as opposed to 60-80 % for sugar coating)
• Coat is less likely to affect disintegration
• Single stage process an so generally quicker
• Easy to automate (less reliance on skilled operator / easier to meet GMP requirements of SOPs, validation etc) Maintains original shape of the core & allows for embossing
• Expensive equipment & plant requires large space
• High installation & energy costs

Aqueous vs Solvent Film Coating

Solvent-based coating solutions / suspensions (e.g. alcohols, methylene chloride)

• rapid drying time due to inherent volatility
• can be applied to moisture sensitive products
• operator safety issues
• requires modification to equipment and facility (flame-proofing / intrinsically safe)
• environmentally responsible disposal is expensive (solvent recovery)
• can impart taste/ smell to the product

Aqueous based processes are now the most common

• no safety issues (e.g. can allow mobile vessels)
• can release to atmosphere
• takes longer and may lead to mechanical damage as tablets are tumbled for longer
• requires more efficient drying air plant

Advances in drying efficiency have allowed aqueous processes to be developed even for moisture sensitive products

Film Coating - The Process

• The coater drum rotates and the baffles in the drum mix the tablets
• Warm air is drawn through the bed as it enters (inlet air) and exist (outlet air) the drum through perforations

• The distance from the spray guns to the tablet bed is measured and the spray adjusted to achieve and even (non overlapping) coverage across ~75% of the bed
• The coating suspension is pumped through the spray guns with compressed (atomising) air which forms a spray of fine droplets
• As the suspension droplets hit the tablet surface they should spread into a film before the solvent is rapidly removed by the throughput air 
• The aim is to gradually build up the coat as the tablets pass beneath the spray guns

Common Components of a Film Coat

• Solvents
- water
- solvents
• alcohols (e.g. ethanol, isopropanol)
• esters (e.g. ethyl acetate, ethyl lactate)
• chlorinated hydrocarbons (e.g. methylene chloride, 1:1:1 trichloroethane)
• Polymers / Film Formers
- form a clear, non-tacky, mechanically strong film
- must be soluble in the chosen solvent and also allow the release of drug in the body
- must be compatible with the core contents most common example is Hydroxy propyl methyl cellulose (HPMC)
• Plasticisers
- modify the properties of the polymer to assist the coating process (e.g. by reducing brittleness of the coat)
- need to be miscible with the polymer e.g. propylene glycol, polyethylene glycol (PEG)
• Colourants
- water-insoluble pigments or water-soluble dyes e.g. yellow or red iron oxide, aluminium lake dyes
• Opacifiers
- provide a “hiding” function preventing the coat from being see through
- used to mask core color and or provide light protection e.g. titanium dioxide