COATING OF TABLET

BY,

MD. SHAFIQUL ISLAM

(Compliance officer)

ACI LTD.

DEFINITION

Tablet coating is the application of a coating

material to the exterior of a tablet with the

intention of conferring benefits and properties

the 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 COMPONENTS

INVOLVED 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

Polishing

Sealing/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 COATING Subcoating: 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 FLIM COATING 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

core. Usually not as shiny as

sugar coat type

Rounded with high degree

of polish

Weight increase

because of coating

material

2-3% 30-50%

Logo or ‘break lines’ Possible Not Possible

Process stages Usually single stage Multistage process

Typical batch coating

time

1.5 to 2.0 Hours Eight hours but easily

longer

Functional coatings Easily adaptable for

controlled release

Not usually possible apart

from enteric coating

COATING MACHINE

1=Inlet air, 2=Inlet air filter and air heater

3=Coating pan, 4=Compressed air,

5=Pneumatic spray 6=Outlet air

7=Container with pneumatic stirrer 8=Peristaltic pump

(Control pressure 5-6 bar, Atomizing air pressure 1-2 bar)

Fig : Coating Machine Fig: Typical Spry Gun

CHECKPOINTS OF TABLET COATING 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 TABLET

COATINGIMPORTANT 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 COATINGCheck 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 TABLETSticking 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 TABLETRoughness: 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 TABLETOrange Peel: Inadequate spreading of coating solution before

drying causes a bumpy or Orange –peel effects on the coating.

Fig: Orange PeelCauses :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 TABLETColour 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 TABLETCracking : 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 OF

COATED TABLETSFilm-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 get

better results when we apply a little science to it.

THANKS TO ALL