COATING OF TABLETBY,MD. SHAFIQUL ISLAM(Compliance officer)ACI LTD.
DEFINITIONTablet coating is the application of a coatingmaterial to the exterior of a tablet with theintention of conferring benefits and propertiesthe dosage form over the uncoated variety.
PURPOSE OF TABLET COATING Cover the unpleasant taste, odor and color. Physical and chemical protection in medicine from environment (light, moisture, and air). Control of drug release as in enteric coating or sustained release or more usually to coated multi particulates. To protect drug from the gastric environment of the stomach with an acid-resistant enteric coating. Improve the appearance of tablets. Assist and facilitate the identification of drug. Easing the process of blistering.
PRIMARY COMPONENTSINVOLVED IN TABLET COATING There are three primary components involved in tablet coating: 1. Tablet properties. 2. Coating process. → Coating equipment. → Parameters of coating process. → Facility and ancillary equipment. → Automation in coating process. 3. Coating composition.
TYPES OF TABLET COATING Various kinds of tablet coating Sugar coating Film coating Enteric coating Press coating
SUGER COATING Sugar coating is a multistage process and can be divided into the following steps: Sealing of the tablet cores Sub coating Smoothing Coloring PolishingSealing/Water proofing: Provides a moisture barrier and harden the tablet surface. e.g. :Shellac, Zine, Cellulose acetate phthalate (CAP), Polyvinylacetate phthalate, Hyroxylpropylcellulose, Hyroxypropylmet hylcellulose etc
SUGER COATINGSubcoating: Causes a rapid buildup to round off the tablet edges. Generally two methods are used for subcoating:1)The application of gum based solution followed by dusting with powder and then drying. This routine is repeated until the desired shape is achieved. 2)The application of a suspension of dry powder in gum/sucrose solution followed by drying. III. Grossing/Smoothing: It is specifically for smoothing and filing the irregularity on the surface generated during subcoating. It also increases the tablet size to a predetermined dimension. IV. Colouring: Gives the tablet its colour and finished size. V. Polishing: Produces the characteristics gloss. Polishing is achieved by applying the mixture of waxes like beeswax, carnubawax, candelila wax or hard paraffin wax to tablets in polishing pan.
FILM COATING Involves spraying a solution of polymer + pigments + plasticizers on to a rotated, mixed tablet bed forms a thin, uniform film on tablet surface. Coating suspension formulation: Typically this comprises: Polymer Plasticizer Colourants Solvent.
IDEAL CHARACTERISTICS A FLIMCOATING POLYMER Solubility: For conventional film coating the polymer should have good solubility in aqueous fluids to facilitate the dissolution of the active ingredient from the finished dosage form. However, where a modified-release action is required then a polymer system of low water solubility or permeability will be chosen. Viscosity: Polymers should have a low viscosity for a given concentration. This will permit the easy, trouble- free spraying of their solutions in industrial film coating equipment. Permeability: Film coating can be used to optimize the shelf-life of a tablet preparation, as some polymers are efficient barriers against the permeability of water vapour or other atmospheric gases. These properties vary widely between the individual polymers.
PLISTICIZER Plasticizers are generally added to film coating formulations to modify the physical properties of the polymer to make it more usable. One important property is their ability to decrease film brittleness. Examples of plasticizers are: Polyols, such as polyethylene glycol 400 Organic esters, such as diethyl phthalate Oils/glycerides, such as fractionated coconut oil. In general, only water-miscible plasticizers can be used for aqueous-based spray systems.
COLOURANTS Any permitted colourants in a film coat formula are invariably water-insoluble colours (pigments). Pigments have certain advantages over water-soluble colours: they tend to be more chemically stable towards light, provide better opacity and covering power, and optimize the impermeability of a given film to water vapour.Examples of colourants are:• Iron oxide pigments• Titanium dioxide• Aluminium Lakes.
SOLVENTS Modern techniques now rely on water as a polymer solvent because of the significant drawbacks that readily became apparent with the use of organic solvents. The disadvantages of organic solvents for the process: 1. Environmental: the venting of untreated organic solvent vapor into the atmosphere is ecologically unacceptable, and efficient solvent vapor removal from gaseous effluent is expensive.2. Safety: organic solvents provide explosion, fire and toxic hazards to plant operators.3. Financial: the use of organic solvents necessitates the building of flame- and explosion-proof facilities. Ingredient cost is also comparatively high, and the associated costs of storage and quality control must also be taken in to consideration.
ENTERIC COATED TABLET This technique is used to protect 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 active constituents unstable at low pH. To protect the stomach from the irritant effect of certain drugs. To facilitate absorption of a drug that is preferentially absorbed distal to the stomach. Polymer are insoluble in aqueous media at low pH, but as the pH rises they experience a sharp, well defined increase in solubility at a specific pH.
PRESS COATING Use of compression to form coat around a pre-formed core. Fig: Press coated tablet Used mainly to separate chemically incompatible materials. Also dual release patterns possible Compression coating is a dry process.
MAJOR DIFFERENCES BETWEEN SUGER& FILM COATING FEATURES FILM COATING SUGAR COATING Appearance Retain contour of original Rounded with high degree core. Usually not as shiny as of polish sugar coat type Weight increase 2-3% 30-50% because of coating material Logo or ‘break lines’ Possible Not Possible Process stages Usually single stage Multistage process Typical batch coating 1.5 to 2.0 Hours Eight hours but easily time longer Functional coatings Easily adaptable for Not usually possible apart controlled release from enteric coating
COATING MACHINE Fig : Coating Machine Fig: Typical Spry Gun1=Inlet air, 2=Inlet air filter and air heater3=Coating pan, 4=Compressed air,5=Pneumatic spray 6=Outlet air7=Container with pneumatic stirrer 8=Peristaltic pump (Control pressure 5-6 bar, Atomizing air pressure 1-2 bar)
CHECKPOINTS OF TABLETCOATING Check that coating Suite are properly cleaned & dry. All correct documents are available Check for QC approved (Green) status label and the re- testing date on the container. Check that all balance are calibrated. Check that correct dispensed RM is available Check the gross weight of the container to be dispensed and the quantity matches with the labeled quantity. Monitor that during material handling the operator should wear mask and gloves. Monitor every step of coating. Any deviation during coating process should be immediately take initiative to resolve.
CHECKPOINTS OF TABLETCOATING IMPORTANT PROCESSING PARAMETERS Inlet & Outlet of bed temperatures. Relative humidity. Atomization air pressure. Pan speed. Liquid spray rate. Gun nozzles check. Spray gun calibration. Solid content of coating solution. Nozzle-to-bed distance. Droplet size. Drying time
CHECKPOINTS OF COATING Check the appearance of coated tablets paying attention to the Color variation Sticking Twinning Cracking Capping Lamination Broken tablet Orange peel Fibers Black spot Oil spot, etc.
PROBLEM OF COATED TABLET Sticking and picking Roughness Orange peel Color variation Cracking Twinning Capping Lamination Blistering Catering
PROBLEM OF COATED TABLET Sticking and picking: Over wetting or excessive film thickness causes tablets to stick each other or to the coating pan. - On drying at the point of contact, a piece of film may remain adhere to pan or tablet. - Giving “picked” appearances to the tablet surface. - Resulting in a small exposed area of the core. Remedies: Reduction in liquid application rate. Increase in drying air temperature and air volume.
PROBLEM OF COATED TABLET Roughness: A rough or gritty surface observed when the coating is applied by spray. Causes : Some of the droplets may dry too rapidly before reaching the tablet bed and deposits on tablet surface. On tablet surface spray- dried particles of finely divided droplets of coating solution. Surface roughness also increases with pigment concentration and polymer concentration in the coating solution. Remedies : • Moving the nozzle closer to the tablet bed. • Reducing the degree of atomization can decrease the roughness due to spray drying .
PROBLEM OF COATED TABLET Orange Peel: Inadequate spreading of coating solution before drying causes a bumpy or Orange –peel effects on the coating. Fig: Orange Peel Causes :Indicates that spresding is impaired by rapid rate of drying or by high solution viscosity. Remedies : Thinning of coating solution with additional solvents may correct this problem.
PROBLEM OF COATED TABLET Colour variation: Colour variation Problem caused by process conditions or the formulation Improper mixing, uneven spray pattern and insufficient coating may results in colour variation. The migration of soluble dyes, plasticizer and other additives give the coating a mottled or spotted appearance. Fig: Colour variation tablet Remedies : Proper mixing of coating solution • Spray uniformly • Use of lake dyes eliminates dye migration. • A reformulation with different plasticizer and additives is the best way to solve film instability.
PROBLEM OF COATED TABLET Cracking : Cracking occurs if internal stresses in the film exceed the tensile strength of the film. The tensile strength of the film can be increased by using higher molecular –weight polymers or polymer blends. Remedies: Adjusting the plasticizer types and concentration can minimize internal stresses Also adjusting the pigment types and concentration can minimize internal stresses Blistering : Evaporation of solvents from the core in the oven. And effect of high temperature on the strength, elasticity and adhesion of the film may results in blistering. Remedies :Controlled drying conditions.
PROBLEM OF COATED TABLETTwinning: Two or more tablets are stick together. Unbalancing the pan speed. Hi spray rate. Fig: Twinning effect Remedies: This problem can be solve by balancing the pan speed and spray rate
IDEAL CHARACTERISTICS OFCOATED TABLETS Film-coated tablets must comply with the uniformity of mass test unless otherwise justified and authorized Film-coated tablets comply with the disintegration test. Film-coated tablets should display An even coverage of film and colour. No abiasion of tablet edges or crowns. Logos and break lines should be distinct and not filled in. The tablet must also be within specifications and any relevant compendial requirements. Tablets must comply with finished product specifications and any appropriate compendial requirements. Sugar-coated tablets should ideally be of a perfectly smooth rounded contour with even colour coverage. Most manufacturers take advantage of the aethetic appeal of a sugar-coated tablet and polish to a high gloss. Any printing should be distinct, with no smudging or broken print.
Coated tablets Store Store the coated tablets in plastic drum with double polythene bags with silica gel between the bags & close the poly bags and fix-up lids of the plastic drum properly. Label the plastic drum with Product name, Batch No, Gross tare & Net weight ,Drum number & signature of the authorized person.
Coating may be something of an art, but we’ll getbetter results when we apply a little science to it. THANKS TO ALL