INTRODUCTION:

Many tablets today are coated after being pressed. Although sugar-coating was popular in the past, the process has many drawbacks. Modern tablet coatings are polymer and polysaccharide based, with plasticizers and pigments included. Coatings are necessary for tablets that have an unpleasant taste, and a smoother finish makes large tablets easier to swallow. Tablet coatings are also useful to extend the shelf-life of components that are sensitive to moisture or oxidation. opaque materials like titanium dioxide can protect light-sensitive actives from photo degradation.

If the active ingredient of a tablet is sensitive to acid, or is irritant to the stomach lining, an enteric coating can be used, which is resistant to stomach acid and dissolves in the high pH of the intestines. Enteric coatings are also used for medicines that can be negatively affected by taking a long time to reach the small intestine where they are absorbed. to protect the tablet Temperature, Humidity, Mask the taste.

REASONS OF TABLET COATING:^(1,2)

a) Controlling site of drug release.

b) Providing controlled continuous release or reduces the frequency of drug dosing.

c) Maintaining physical or chemical drug integrity.

d) Enhancing product acceptance and appearance.

Many solid pharmaceutical dosage mediums are produced with coatings, either on the external surface of tablets, or on materials dispensed within gelatine capsules.

PURPOSES OF TABLET COATING:^(1,2)

1) Protects the tablet (or the capsule contents) from stomach acids.

2) Protects the stomach lining from aggressive drugs such as enteric coated aspirin.

3) Provides a delayed release of the medication.

4) Helps maintain the shape of the tablet.

Ideally, the tablet should release the material gradually and the drug should be available for digestion beyond the stomach. The coating can be specially formulated to regulate how fast the tablet dissolves and where the active drugs are to be absorbed into the body after ingestion.

Many factors can affect the end-use properties of Pharmaceutical tablets:

1. Chemical composition

2. Coating process

3. Drying time

4. Storage and environmental monitoring.

OBJECTIVE OF TABLET COATING^(3,4):

1. Mask the odour, taste or color of the drug.

2. Provide Physical and Chemical protection for Drug.

3. Control the release of drug from the tablet.

4. Protects the drug from gastric environment of stomach in case acid sensitive drug.

5. Avoids chemical Incompatibility.

6. Improves Pharmaceutical elegance by using colors and contrasting Printing.

COATING PROCESS DESIGN AND CONTROL:

Tablet coating takes place in a controlled atmosphere inside a perforated rotating drum. Angled baffles fitted into the drum and air flow inside the drum provide means of mixing the tablet bed. As a result, the tablets are lifted and turned from the sides into the centre of the drum, exposing each tablet surface to an even amount of deposited/sprayed coating.

The liquid spray coating is then dried onto the tablets by heated air drawn through the tablet bed from an inlet fan. The air flow is regulated for temperature and volume to provide controlled drying and extracting rates, and at the same time, maintaining the drum pressure slightly negative relative to the room in order to provide a completely isolated process atmosphere for the operator.

Tablet coating equipment may include spray guns, coating pan, polishing pans, solution tanks, blenders and mixers, homogenizers, mills, peristaltic pumps, fans, steam jackets, exhaust and heating pipes, scales and filters. Tablet coating processes may include sugar coating (any mixtures of purified water, cellulose derivatives, polyvinyl, gums and sugar) or film coating (purified water, cellulose derivatives).

The coating process is usually a batch driven task consisting of the following phases:

1. Batch identification and Recipe selection (film or sugar coating)

2. Loading/Dispensing (accurate dosing of all required raw materials)

3. Warming

4. Spraying (application and rolling are carried out simultaneously)

5. Drying

6. Cooling

7. Unloading

A control system must therefore provide flexibility in the way in which accurate and repeatable control of the coating environment is achieved and will include the following features:

1) Precise loop control with set point profile programming.

2) Recipe Management System for easy parameterization.

3) Sequential control for complex control strategies.

4) Secure collection of on-line data from the coating system.

5) Analysis and evidence.

Local operator display with clear graphics and controlled access to parameters

Coating process:

The basic principle of tablet coating is simple. Tablet coating is an application of coating composition to a moving bed of tablets with the concurrent use of heated air to facilitate evaporation of the solvent. The distribution of coating is accomplished by the movement of the tablets either perpendicular (coating pan) or vertical (air suspension).

A. Coating equipments:

For the coating process use of one of the 3 types of following equipments.

1) Conventional coating pan.

2) The perforated coating pan.

3) The fluidized bed coater.

1) Conventional coating pan:

Improvements in conventional pan are pellegrini system which has a baffled pan and diffuser The immersion sword system and the immersion tube system all of them have enhanced drying efficiency compared to older models. The newer models are completely enclosed.

2) The perforated coating pan:

The e.g. in this class are Accela-cota, Hi-Coater system Diracoater and the Glatt coater.

3) The fluidized bed coater:

The fluidized bed coaters have enhanced drying efficiency fluidization of tablet mass is achieved by columnar chamber by the upward movement of the drying air. The movement of the tablets is upward through the center of the camber. Then they fall toward the chamber wall and move downward to re-enter into air stream at the bottom of the chamber. It has a basically two spray application systems they are (1) high pressure airless (2) low pressure air atomized.

COATING TECHNIQUES^(6,7):

Generally three methods are used for tablet coating

A) Sugar coating.

B) Film coating.

C) Enteric coating.

A) Sugar coating:

I. Sealing/Water proofing: provides a moisture barrier and harden the tablet surface.

II. Sub coating causes a rapid buildup to round off the tablet edges.

III. Grossing/Smoothing: smoothes out the sub coated surface and increases the tablet size to Predetermine dimension.

IV. Coloring gives the tablet its color and finished size.

V. Polishing produces the characteristics gloss.

B) Film coating: -

Film coating and the sugarcoating share same equipment and the process parameters. There are basically 2 methods of film coating they are

I. Pan pour methods:

Tablets coated by pan pour method subjected to alternate solution application, mixing and drying steps are similar to pan pour sugar coating. This method is relatively slow and relies heavily on the skill of operator.

II. Pan-spray methods:

The introduction of spraying equipment was the next evolution in improving the film coating process allows for automated control of liquid application. Broad flat spray patterns are usually chosen by appropriate nozzle systems.

Process description:

Film coating is deposition of a thin film of polymer surrounding the tablet core. Conventional pan equipments may be used but now a day's more sophisticated equipments are employed to have a high degree of automation and coating time. The polymer is solubilized into solvent. Other additives like plasticizers and pigments are added. Resulting solution is sprayed onto a rotated tablet bed. The drying conditions cause removal of the solvent, giving thin deposition of coating material around each tablet core.

Process details:

Usually spray process is employed in preparation of film coated tablets. Accela cota is the prototype of perforated cylindrical drum providing high drying air capacity. Fluidized bed equipment has made considerable impact where tablets are moving in a stream of air passing through the perforated bottom of a cylindrical column. With a smaller cylindrical insert, the stream of cores is rising in the center of the device together with a spray mist applied in the middle of the bottom. For fluidized bed coating, very hard tablets (hardness > 20 N) have to be used.

Basic process requirements for film coating:

The fundamental requirements are independent of the actual type of equipments being used and include adequate means of atomizing the spray liquid for application to the tablet core, adequate mixing and agitation of tablet bed, sufficient heat input in the form of drying air to provide the latent heat of evaporation of the solvent. This is particularly important with aqueous-based spraying and good exhaust facilities to remove dust and solvent laden air

Development of film coating formulations:

Colour, shape and size of final coated tablet are important for marketing and these properties have a significant influence on the marketing strategies. An experienced formulator usually takes the pragmatic approach and develops a coating formulations modification of one that has performed well in the past. Spraying or casting films can preliminarily screen film formulations. Cast films cab is prepared by spreading the coating composition on teflon, glass or aluminum foil surface using a spreading bar to get a uniform film thickness. Sprayed films can be obtained by mounting a plastic-coated surface in a spray hood or coating pan.

Coating formula optimization:

Basic formula is obtained from past experience or from various sources in the literature. Modifications are required to improve adhesion of the coating to the core, to decrease bridging of installations, to increase coating hardness, etc. Usually concentration of colorant and opaquant are fixed to get predetermined shade. Common modification is to alter polymer-to-plasticizer ratio or addition of different plasticizer/ polymer. Experimentation of this type can be best achieved by fractional

Materials used in film coating:

I. Film formers, which may be enteric or nonenteric

II. Solvents

III. Plasticizers

IV. Colourants

V. Opaquant-Extenders

VI. Miscellaneous coating solution components

I. FILM FORMERS^(4,5):

Ideal requirements of film coating materials are summarized below:

i) Solubility in solvent of choice for coating preparation

ii) Solubility requirement for the intended use e.g. free water-solubility, slow water-solubility or pH -dependent solubility

iii) Capacity to produce an elegant looking product

iv) High stability against heat, light, moisture, air and the substrate being coated

v) No inherent colour, taste or odor

vi) High compatibility with other coating solution additives

vii) Nontoxic with no pharmacological activity

viii) High resistance to cracking

ix) Film former should not give bridging or filling of the debossed tablet

x) Compatible to printing procedure

Commonly used film formers are as follow

Hydroxy Propyl Methyl Cellulose (HPMC):

It is available in different viscosity grades. It is a polymer of choice for air suspension and pan spray coating systems because of solubility characteristic in gastric fluid, organic and aqueous solvent system.

Advantages include: it does not affect tablet disintegration and drug availability, it is cheap, flexible, highly resistant to heat, light and moisture, it has no taste and odor, colour and other additives can be easily incorporated.

Disadvantage includes: when it is used alone, the polymer has tendency to bridge or fill the debossed tablet surfaces. So mixture of HPMC and other polymers/ plasticizers is used.

Methyl Hydroxy Ethyl Cellulose (MHEC):

It is available in wide variety of viscosity grades. It is not frequently used as HPMC because soluble in fewer organic solvents.

Ethyl Cellulose (EC):

Depending on the degree of ethoxy substitution, different viscosity grades are available. It is completely insoluble in water and gastric fluids. Hence it is used in combination with water-soluble additives like HPMC and not alone. Unplasticized ethyl cellulose films are brittle and require film modifiers to obtain an acceptable film formulation. Aqua coat is aqueous polymeric dispersion utilizing ethyl cellulose. These pseudolatex systems contain high solids, low viscosity compositions that have coating properties quite different from regular ethyl cellulose solution.

Hydroxy Propyl Cellulose (HPC):

It is soluble in water below 40^oc (insoluble above 45^oC), gastric fluid and many polar organic solvents. HPC is extremely tacky as it dries from solution system. It is used for sub coat and not for colour or glass coat. It gives very flexible film.

Povidone:

Degree of polymerization decides molecular weight of material. It is available in four viscosity grades i.e. K-15, K-30, K-60 and K-90. Average molecular weight of these grades is 10000, 40000, 160000 and 360000 respectively. K-30 is widely used as tablet binder and in tablet coating. It has excellent solubility in wide variety of organic solvents, water, gastric and intestinal fluids. Povidone can be cross-linked with other materials to produce films with enteric properties. It is used to improve dispersion of colourants in coating solution.

Sodium Carboxy Methyl Cellulose:

It is available in medium, high and extra high viscosity grades. It is easily dispersed in water to form colloidal solutions but it is insoluble in most organic solvents and hence not a material of choice for coating solution based on organic solvents. Films prepared by it are brittle but adhere well to tablets. Partially dried films of are tacky. So coating compositions must be modified with additives.

Polyethylene glycols (PEG):

Lower molecular weights PEG (200-600) are liquid at room temperature and are used as plasticizers. High molecular weights PEG (900-8000series) are white, waxy solids at room temperature. Combination of PEG waxes with CAP gives films that are soluble in gastric fluids.

Acrylate polymers:

It is marketed under the name of Eudragit. EudragitE is cationic co-polymer. Only EudragitE is freely soluble in gastric fluid up to pH 5 and expandable and permeable above pH 5. This material is available as organic solution (12.5% in isopropanol/acetone), solid material or 30% aqueous dispersion. EudragitRL & RS are co-polymers with low content of quaternary ammonium groups. These are available only as organic solutions and solid materials. They produce films for delayed action (pH dependent).

II. Solvents:

Solvents are used to dissolve or disperse the polymers and other additives and convey them to substrate surface.

Ideal requirement are summarized below:

i) Should be either dissolve/disperse polymer system

ii) Should easily disperse other additives into solvent system

iii) Small concentration of polymers (2-10%) should not in an extremely viscous solution system creating processing problems

iv) Should be colourless, tasteless, odorless, inexpensive, inert, nontoxic and nonflammable

v) Rapid drying rate

vi) No environmental pollution

Mostly solvents are used either alone or in combination with water, ethanol, methanol, isopropanol, chloroform, acetone, methylene chloride, etc. Water is more used because no environmental and economic considerations. For drugs that readily hydrolyze in presence of water, non aqueous solvents are used.

III. Plasticizers:

As solvent is removed, most polymeric materials tend to pack together in 3-D honey comb arrangement. "Internal" or "External" plasticizing technique is used to modify quality of film. Combination of plasticizer may be used to get desired effect. Concentration of plasticizer is expressed in relation to the polymer being plasticized. Recommended levels of plasticizers range from 1-50 % by weight of the film former. Commonly used plasticizers are castor oil, PG, glycerin, lower molecular weight (200-400 series), PEG, surfactants, etc. For aqueous coating PEG and PG are more used while castor oil and spans are primarily used for organic-solvent based coating solution. External plasticizer should be soluble in the solvent system used for dissolving the film former and plasticizer. The plasticizer and the film former must be at least partially soluble or miscible in each other.

IV. Colourants:

Colourants can be used in solution form or in suspension form. To achieve proper distribution of suspended colourants in the coating solution requires the use of the powdered colourants (<10 microns). Most common colourants in use are certified FD & C or D & C colourants. These are synthetic dyes or lakes. Lakes are choice for sugar or film coating as they give reproducible results. Concentration of colourants in the coating solutions depends on the colour shade desired, the type of dye, and the concentration of opaquant-extenders. If very light shade is desired, concentration of less than 0.01 % may be adequate on the other hand, if a dark colour is desired a concentration of more than 2.0 % may be required. The inorganic materials (e.g. iron oxide) and the natural colouring materials (e.g. anthrocyanins, carotenoids, etc) are also used to prepare coating solution. Magenta red dye is non absorbable in biologic system and resistant to degradation in the gastro intestinal track. Opasray(opaque colour concentrate for film coating) and Opadry(complete film coating concentrate) are promoted as achieving less lot-to-lot colour variation.

V. Opaquant-Extenders:

These are very fine inorganic powder used to provide more pastel colours and increase film coverage. These inorganic materials provide white coat or mask colour of the tablet core. Colourants are very expensive and higher concentration is required. These inorganic materials are cheap. In presence of these inorganic materials, amount of colourants required decreases. Most commonly used materials are titanium dioxide, silicate (talc &aluminum silicates), carbonates (magnesium carbonates), oxides (magnesium oxide) & hydroxides (aluminum hydroxides). Pigments were investigated in the production of opaque films and it was found that they have good hiding power and film-coated tablets have highlighted intagliations.

VI. Miscellaneous coating solution component:

Flavors, sweeteners, surfactants, antioxidants, antimicrobials, etc. may be incorporated into the coating solution.

C. ENTERIC COATING:

An enteric coating is a barrier applied to oral medication that controls the location in the digestive system where it is absorbed. Enteric refers to the small intestine; therefore enteric coatings prevent release of medication before it reaches the small intestine..

Gastro-resistant tablets are delayed-release tablets that are intended to resist the gastric fluid and to release their active substance(s) in the intestinal fluid. Usually they are prepared from granules or particles already covered with a gastro-resistant coating or in certain cases by covering tablets with a gastro-resistant coating (enteric-coated tablets). Tablets covered with a gastro-resistant coating conform to the definition of coated tablets.

Most enteric coatings work by presenting a surface that is stable at the highly acidic pH found in the stomach, but breaks down rapidly at a less acidic (relatively more basic) pH. For example, they will not dissolve in the acidic juices of the stomach (pH ~3), but they will in the higher pH (above pH 5.5) environment present in the small intestine. Materials used for enteric coatings include fatty acids, waxes, and shellac as well as plastics.

COMPOSITION OF COATING:^(8,9)

1) Cellulose acetate phthalate (CAP)

2) Methyl acrylate-methacrylic acid copolymers

3) Cellulose acetate succinate

4) Hydroxy propyl methyl cellulose phthalate

5) Hydroxy propyl methyl cellulose acetate succinate (hypromellose acetate succinate)

6) Polyvinyl acetate phthalate (PVAP)

7) Methyl methacrylate-methacrylic acid copolymers

8) Sodium alginate and Stearic acid

The active ingredients contained in these are then better protected against heat, light, moisture and other harmful influences during transport and storage. Some Polymers are resistant to gastric fluid e.g. EUDRAGIT. Medication that causes incompatibilities in the stomach i.e. irritates the gastric mucosa or provokes nausea and sickness can be coated with these enteric films to pass the acid environment of the stomach unchanged and release the active only after entering the small intestine.

After leaving the stomach, the chyme is approximately neutralized by the addition of pancreatic fluid, resulting in a pH of 5 to 6 in the duodenum. In the lower sections of the small intestine, the pH continues to increase gradually, sometimes up to a value of 7. In the colon, pH values of approximately 6.5 to 7 are found. Enteric polymer films are normally expected to dissolve between pH 5.5 and 6.5, on the one hand to avoid premature disintegration in the stomach and, Using EUDRAGIT® S, dissolution of enteric film coatings only sets in above pH 7 and thus occurs in vivo in the lower sections of the intestines.

Controlled and localized release of drugs in the intestine can be achieved by enteric coating. The design of enteric-coated tablets has so far remained empirical, in part because of the lack of a quantitative description of the drug release kinetics. The dissolution of the enteric coating is found to depend on the intrinsic solubilities and pKa of the drug and polymer and the medium properties. The release rate of the drug is found to depend on the intrinsic solubilities and pKa of drug and polymer, the medium properties, i.e., pH and buffer capacity, and a mass transfer coefficient.

The coating solution used to prepare the enteric coating layer on the tablets according to this invention may contain the enteric polymer over a range of concentrations. In general this will amount to about 5% to about 15% by weight of enteric polymer based on the total weight of the coating solution with the preferred range being from about 9% to about 12% on the same weight basis.

A special advantage of aqueous synthetic polymer dispersions employed in this invention is that the water is merely a dispersing agent and not a solvent for the polymer. This means that water is not retained by the lacquer substance during the formation of the film but evaporates rapidly and almost completely. This aspect is extremely important especially for coating drugs that are highly moisture sensitive such as aspirin.

ENTERIC COATING PARAMETERS^(11,12):

Dissolution:

Dissolution test for enteric coated tablets is performed in two stages

i) Acid stage

ii) Buffer stage

Acid stage:

Place 900 ml of 0.1 N HCl is placed in the dissolution apparatus and assemble the apparatus. Maintain the temperature at 37±0.5^oC. Operate the apparatus for 2 hrs at 75 rpm. After 2 hrs with draw an aliquot of the fluid, and proceed immediately as directed under buffer stage. Measure the amount of drug release by measuring the absorbance at 306 nm in a UV/Visible spectrophotometer.

Buffer stage:

Darin the acid from vessel and add 900 ml of pH6.8 phosphates buffer and maintain the temperature at 37±0.5^oc. Operate the apparatus at 75 rpm for 60 mins. Collect the samples at regular time intervals. Measure the amount of drug release by measuring the absorbance at 254 nm in a UV/Visible spectrophotometer.

Table No. 1. Acceptance criteria for dissolution of enteric coated tablets Acid stage

Level	Number tested	Criteria
A₁	6	No individual value exceeds 10% dissolved.
A₂	6	Average of the 12 units (A₁+A₂) is not more than dissolved, and no individual unit is greater than 25% dissolved.
A₃	12	Average of the 24 units (A₁+A₂+A₃) is not more than 10% dissolved, and no individual unit is greater than 25% dissolved.

Table No. 2. Buffer stage

Level	Number tested	Criteria
B1	6	Each unit is not less than Q+5%.
B2	6	Average of the 12 units (B1+B2) is equal to or greater than Q, and no unit is less than Q-15%.
B3	12	Average of the 24 units (B1+B2+B3)is equal to or greater than Q, not more than 2 units are less than Q-15% ,and no unit is less than Q-25%.

Disintegration:

Acid stage:

0.1N HCL for 2 hours. No cracks on the tablets.

Buffer stage: 6.8 phosphate buffer for 1 hour

Enteric coating:

This type of coating is used to protect tablet core from disintegration in the acid environment of the stomach for one or more of the following reasons:

i) To prevent degradation of acid sensitive API

ii) To prevent irritation of stomach by certain drugs like sodium salicylate

iii) Delivery of API into intestine

iv) To provide a delayed release component for repeat action tablet

Several kinds of enteric layer systems are now available

One layer system:

The coating formulation is applied in one homogeneous layer, which can be whites-opaque or colored. Benefit is only one application needed.

Two layer system:

To prepare enteric tablets of high quality and pleasing appearance the enteric formulation is applied first, followed by coloured film. Both layers can be of enteric polymer or only the basic layer contains enteric polymer while top layer is fast disintegrating & water-soluble polymer.

IDEAL PROPERTIES:

Ideal properties of enteric coating material are summarized as below

i) Resistance to gastric fluids

ii) Susceptible/permeable to intestinal fluid

iii) Compatibility with most coating solution components and the drug substrate

iv) Formation of continuous film

v) Nontoxic, cheap and ease of application

vi) Ability to be readily printed

Polymers used for enteric coating are as follow

Cellulose acetate phthalate (CAP):

It is widely used in industry. Aquateric is reconstituted colloidal dispersion of latex particles. It is composed of solid or semisolid polymer spheres of CAP ranging in size from 0.05 - 3 microns. Cellulose acetate trimellitate (CAT) developed as an ammoniated aqueous formulation showed faster dissolution than a similar formulation of CAP.

Disadvantages include: It dissolves above pH 6 only, delays absorption of drugs, it is hygroscopic and permeable to moisture in comparison with other enteric polymer, it is susceptible to hydrolytic removal of phthalic and acetic acid changing film properties. CAP films are brittle and usually used with other hydrophobic film forming materials.

Acrylate polymers:

Eudragit RL and Eudragit RS are two forms of commercially available enteric acrylic resins. Both of them produce films resistant to gastric fluid. EudragitRL & RS are soluble in intestinal fluid at pH 6 & 7 respectively. EudragitRL is available as an organic solution (Isopropanol), solid or aqueous dispersion. EudragitRS is available only as an organic solution (Isopropanol) and solid.

Hydroxy Propyl Methyl Cellulose Phthalate:

HPMCP 50, 55 & 55-s (also called HP-50, HP-55 & HP-55-s) is widely used. HP-55 is recommended for general enteric preparation while HP-50 & HP-55-s for special cases. These polymers dissolve at a pH 5-5.5.

Polyvinyl acetate Phthalate:

It is similar to HP-55 in stability and pH dependent solubility.

Controlled release coating:

Polymers like modified acrylates, water insoluble cellulose (ethyl cellulose), etc. used for control release coating.

Film coating:

Film coating is deposition of thin film of polymer surrounding the tablet core. Conventional pan equipments may be used but now-a-days more sophisticated equipments are employed to have a high degree of automation and quality coating. The polymer is solubilised in solvent & other additives like plasticizers and pigments are added. Resulting solution is sprayed onto a rotated tablet bed. The drying conditions cause removal of the solvent, giving thin deposition of coating material around each table.

Factors to be considered during coating process:

1) Check and ensure the coating pan and other equipments are cleaned.

2) Check and ensure that the speed of the coating pan, gun to bed distance, inlet and exhaust air temperature, spray rate, spray type, number of guns, and temperature of the coating solution .

3) After coating is completed, samples are collected for dissolution testing and weight variation.

Coating parameters to be considered:

1. Spray gun model

2. Pan load (kg)

3. Pan speed (rpm)

4. Spray procedure

5. Spray rate (g/min or ml/min)

6. No. of spray guns

7. Distance between spray guns (cm)

8. Distance between spray gun & tablet bed

9. Main inlet pressure (kg/cm²)

10. Atomization pressure (kg/cm²)

11. Inlet air temperature (ºC)

12. Tablet bed temperature (ºC)

13. Position of dampers – inlet, - Outlet

14. Quantity of coating suspension in the liquid vessel (kg/lit)

Process variables during coating:

The variables to be controlled during pan spray film coating processes are:

1. Pan variables:

Pan design/baffling

Speed

Pan load

2. Process- Air:

Air quality

Temperature

Airflow rate/volume/balance

3. Spray variables:

Spray rate

Degree of atomization

Spray pattern

Nozzle to bed distance

Coated tablets evaluation:

A number of test methods are employed:

1) Adhesion tests with tensile strength testers have been used to measure the force required to peel the film from the tablet surface.

2) Diametral crushing strength of coated tablets can be determined with a tablet hardness tester.

3) Coated tablet disintegration and / or dissolution must also be assessed. The coating should have a minimal effect on tablet disintegration or dissolution.

4) Stability studies must be conducted on coated tablets to determine if temperature and humidity changes will cause film defects.

5) Attempts have been made to quantify film surface roughness, hardness and colour uniformity through instrumental means, but in general visual inspection sufficient to define relative coated tablet quality.

ENCAPSULATION OF TABLETS:^(10,11)

The coated tablets can be encapsulated in two different methods

1) Express fits

2) Press fits

Express fits:

The tablets are encapsulated with hard gelatin shells from both sides with a small gap in between the two shells.

Press fits:

The tablets are encapsulated with hard gelatin shells on both sides leaving no gap between the two shells.

Benefits of Press fit and Express fit gelcaps:

1. Meets consumer preferences for a dosage form that is easy-to-swallow.

2. Masks taste and odor

4. Differentiates your brand with a unique trade dress

5. Allows for in-house production

6. Patented technology.

COATING PROCESS DESIGN AND CONTROL:

Enteric coating:

Controlled release coating:

Process variables during coating:

SPECIALIZED COATING:

Compressed coating:

Electrostatic coating:

Dip coating:

Vacuum film coating: