types of tablet coating materials

1. TYPES OF TABLET
COATING MATERIALS
A PRESENTATION MADE BY
PRERNA (Roll No.-1737)
PRIYANSHA (Roll No.- 1738)
B.Pharm Vth semester
SUBMITTED TO- Dr. AMITA SARWAL (Professor of Pharmaceutics)
UNIVERSITY INSTITUTE OF PHARMACEUTICAL SCIENCES, PANJAB UNIVERSITY, CHANDIGARH

2. ABOUT TABLET COATING WITH A TOUCH OF ITS
HISTORY
 Tablet coating is the most critical and the last step in the processing cycle of any tablet. In a
layman’s language it simply means to apply coating to a tablet.
 No discussion on tablet coating is complete when we aren’t aware of its historical review because
then the discussion would not include the evolutions in the patterns and processes of coating.
 The reference for coated solid dosage forms have been made was mentioned in early Islamic drug
literatures. This process was basically adapted from early food preservations and French publications
described it as a means of masking the taste of bitter tasting drugs. Sugar coating was developed in
the 19th century by the French and it patented the use of sugar compositions for coating in cubeb and
copaiba pills. Abbott Laboratories marketed the first film coated tablets in the mid 20th CE

3. THE PRINCIPLES AND OBJECTIVES OF TABLET COATING
 Need of Tablet Coating
1. Mask the taste, odour or colour of the formulated tablet.
2. Provide physical and chemical protection.
3. Protect the drug from gastric environment of the stomach (acid resistant enteric coating)
4. Incorporate the drug of formula adjuvant in the coating to avoid chemical incompatibilities or
to provide a sequential drug release.
5. Control the release of the drug from the tablet.
6. Improve the pharmaceutical elegance by using special colours and contrasting printing
 The 3 components involved in coating process are:-
1. Tablet properties
2. Coating compositions
3. Coating process

4. FACTORS AFFECTING TABLET COATING PROCESSING
 TABLET PROPERTIES: the tablets to be coated must possess proper physical and chemical
characteristics and a proper shape. The tablets roll in the coating pan in an air stream of
an air suspension coater as the coating composition is applied. These also determine the
type and properties of tablet coating materials.
PHYSICAL PROPERTIES OF TABLET: The tablets must be resistant to abrasion and chipping.
Tablet surfaces that are brittle, or soften in the presence of heat, affected by the coating
composition or tend to become rough in the early phase of the coating process are
unacceptable for film coating. Film coating adhere to all exposed surface to cover up all the
imperfections. The quality of film coating depends on the quality of starting tablet. Sugar
coatings cover up the minor points of imperfections.

5. FACTORS EFFECTING TABLET COATING PROCESSING continued…
PHYSICAL SHAPE OF THE TABLET: The tablets must be in a constant motion to prevent the tablet
agglomeration and therefore to prevent tablet agglomeration there must be less surface area for
each tablet to come in contact amongst each other. Spherical tablets allows the minimum surface
area for tablet-to-tablet contact and they can roll freely in the coating pan.
CHEMICAL STABILITY OF THE TABLET MATERIAL: There should be no incompatibilities of the coating
polymer with the tablet excipients and API. Also the tablet material should pose such properties like
hydrophilicity so that when tablet is being coated with a hydrophilic coat, it adheres easily to it. If
the tablet material is hydrophobic the coating composition should comprise of appropriate
surfactants which reduce the surface tension between the tablet and the coating material and
improve its adherence.

6. FACTORS AFFECTING TABLET COATING PROCESSING continued…….
 COATING COMPOSITIONS: The coating materials are a deposition of the material on the
tablet substrate or form a continuous film with a wide variety of properties depending upon
the composition of the coating formulation. Examples of physical deposition of the coating
materials are the techniques of sugar, shellac and wax coatings. Various polymers are also
used. The major coating materials include synthetic polymers, solvents, plasticizers,
colorants, opaque extenders and miscellaneous coating solution components (these
materials are mostly employed for film coating tablets)
TYPES OF TABLET COATING (a bird’s eye view)
1. Film coating of tablets- It is a process in which a tablet is surrounded by a film of
polymeric layer. This type of coating is the most employed.
2. Sugar coating of tablets- It involves the successive application of sucrose based coating
formulations, usually over tablet cores
3. Compressed coating of tablets- It involves the compaction of granular material around a
preformed tablet cores. It is a dry process

7. FILM COATING TABLETS contd……
 An ideal film coating should have the following attributes:-
1. Solubility in solvent of choice for coating preparation.
2. Solubility required for the intended use; e.g. free water solubility, slow water solubility(for controlled
drug release), or pH dependent solubility (for enteric coating)
3. Capacity to produce an elegant looking product.
4. Stability in the presence of heat, light, moisture, air and the substrate being coated. The
film properties should not change with aging.
5. Essential no colour, taste or odour.
6. Compatibility with common coating solution additives.
7. Non toxicity with no pharmacological activity and ease of application to the particles or
tablets.
8. Resistance to cracking and provision of adequate moisture, light, odour or drug sublimation
barrier when desired.
9. Ease of printing procedure on high speed equipment
10. No bridging or filling of the debossed tablet surfaces by the film former.

8. No commercially available material fulfils all requirements of an ideal coating material. Therefore a coating solution has to
be formulated so as to provide certain properties for the film coated product. The available film formers are classified into
non-enteric and enteric materials.
FILM FORMERS (synthetic polymers)
1. Hydroxypropyl Methylcellulose
2. Methyl Hydroxyethylcellulose 1. Cellulose acetate phthalate
3. Ethylcellulose 2. Acrylate polymers
4. Hydroxypropylcellulose 3. Hydroxypropyl methylcellulose phthallate
5. Povidone 4. Polyvinyl acetate phthallate
6. Sodium Carboxymethylcellulose
7. Polyethylene glycols
8. Acrylate polymers
NON ENTERIC
COATING
ENTERIC
COATING

9. NON ENTERIC COATING COMPONENTS:-
These are used to coat those tablets which do not prevent tablets from disintegrating in gastric
environment.
1.HYDROXYPROPYL METHYLCELLULOSE a.k.a. HPMC- This polymer is available in different viscosity
grades. It can be used both in air suspension and in pan spray coating systems. The reasons why it has
gained widespread acceptance include the following facts:-
a) The solubility characteristics of the polymer in GIT fluids and in organic and aqueous solvent
systems.
b) Non interference with tablet disintegration and drug availability.
c) The flexibility, chip resistance, and the absence of taste or odour.
d) stability in the presence of heat, light, air, or reasonable levels of moisture.
e) The ability to incorporate colour and other adjuncts into the film without incompatibilities.
Disadvantage- filling a debossed tablet surface, but can be overcome by using HPMC with other polymers
or plasticizers.

10. NON ENTERIC COATING COMPONENTS continued……
2. METHYL HYDROXYETHYLCELLULOSE- A wide variety of viscosity grades of this polymer are available. It has similar
structural and chemical similarities with HPMC, but due to its solubility in fewer organic solvents it is not used as
frequently as HPMC.
3. POVIDONE- it is a synthetic polymer having linear1-vinyl-2-pyrrolidinone groups. It is available in various viscosity
grades (evaluated with their K values with K-15 having a molecular weight of 10,000 , K-30 corresponding to 40,000).
Most frequently used povidone is grade K-30 is used as tablet binder and a coating as well. It is soluble in water, GIT
and intestinal fluids and in organic solvents. When dry, povidone films give a hard, glossy and a clear film layer.
Povidone is extremely tacky but its properties can be modified by adding suitable plasticizers, certain polymers and
suspended powders. It also improves colour dispersion in the coating solutions.
4. HYDROXYPROPYLCELLULOSE- It is soluble in water below 40 degrees Celsius, GIT fluids and many other polar
organic solvents. This film becomes extremely tacky when dry and may be desirable for a sub coat but, but not for a
colour for colour or gloss coat. The polymer yield very flexible films. It is usually not used alone but is used with
other polymers to improve the film characters.
5. SODIUM CARBOXYMETHYLCELLULOSE- It is available in various viscosity grades. It is dispersible in water to form
colloidal solutions, but is not soluble in various organic solvents, therefore not suitable for coating solutions based on
organic solutions. The films prepared by sodium CMC are brittle but adhere well to the tablet. Its use in coating
systems are enhanced by using aqueous based film coating efficiency equipments.

11. 6. ETHYLCELLULOSE- it has various viscosity grades. It is completely insoluble in water and GIT fluids thus cannot be
used alone for tablet coating and thus combined with water soluble additives like HPMC with reduced water
solubility properties and is used to prepare sustained release tablets. The polymer is soluble in many organic
solvents and is non-toxic, colourless, odourless, tasteless and stable in environmental condition. Disadvantage is
that it produces brittle ad requires film modifiers to get an acceptable film formulation.
7. POLYETHYLENE GLYCOLS (PEG)- These are used as plasticizers for coating solution films and can be used with
other polymers to enhance film properties- e.g.- combinations of PEG waxes and cellulose acetate phthalate
provide films that are soluble in gastric fluids. Coats produced by using high molecular weight PEGs can be hard,
tasteless, smooth and nontoxic but are sensitive to elevated temperatures.
8. ACRYLATE POLYMERS (marketed as EUDRAGIT)- Eudragit E is a cationic copolymer and 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. Eudragit RL and RS are copolymers synthesized from
acrylic and methacrylic acid esters with a low content of quartenary ammonium groups. These are available only as
their organic solutions and solid materials. These polymer produce films for pH independent preparations.

12. ENTERIC COATING MATERIALS
 Enteric coating of pills and tablets are used to prevent the disintegration of the tablet in the gastrointestinal
environment. Reasons for using coating formulation:
1. Protect acid labile drugs from the gastric enzymes and certain antibiotics
2. Prevent gastric distress or nausea caused due to irritation from a drug (aspirin)
3. Deliver drugs intended for local action in the Intestines e.g.- intestinal antiseptics could be delivered to their
site of action in a concentrated form and bypass systemic absorption in the stomach.
4. Deliver drugs that are optimally absorbed in the small intestines to their primary absorption in their most
concentrated form.
5. Providing a delayed release component for repeat action tablets.
 An ideal enteric coating material has these properties:-
1. Resistance to gastric fluids
2. Ready susceptibility to intestinal fluids
3. Compatibility with most coating solution components and the drug substrate.
4. Stability alone and in coating solutions (the film should not change on ageing)
5. Non toxicity, economic and formation of an uninterrupted film
6. Ease of application without specialized equipment
7. Ability to be readily printed or to allow film to be applied on debossed tablets

13. ENTERIC COATING MATERIALS continued…..
 Although every coating material cannot show all the ideal properties of an enteric coating but a combination of
all the coating compounds used for enteric coating to achieve the desired objective. There are some difficulties
faced while formulating enteric coated tablets.
 Tablet disintegration test where the tablet has to tolerate agitation in simulated gastric fluid test solution at
37+2 degrees Celsius (no disc attached). After an hour of exposure there should be no evidence of disintegration,
cracking or softening. Then a disc is added to each tube and the test is continued using simulated intestinal fluid
at same temperature conditions as of gastric fluid for 2 hours to disintegrate. If tablets disintegrate then they
pass the test.
 All enteric coating must meet these requirements. Just passing the disintegration test by USP doesn’t guarantee
optimum bioavailability of a particular dosage form. Several situations complicate the absorption of drug from
enteric coated tablets. The pH of the stomach contents are variable. Gastric residence time for the dosage form
may range from 0.5-4 hours when food is consumed.
 Most acid labile drugs need protection between pH values of 1-5. An ideal enteric polymer should dissolve near
or above pH 5.
 The retardant type of polymers (non pH dependent solubility)may render the film so thick that they may not be
soluble in intestinal fluids. They act by mechanical hydrophobicity to provide enteric coating effect.

14. TYPES OF ENTERIC COATING MATERIALS
1.CELLULOSE ACETATE PHTHALLATE a.k.a. CAP- though this material is widely employed but it has some disadvantages like it
dissolves at a pH above 6 and thus possibly delay absorption. It is relatively permeable and hygroscopic to moisture and gastric
fluids as compared to the other enteric polymers. CAP films are brittle and are usually formulated with hydrophobic film forming
adjuvants to achieve a better enteric film. E.g. Aquateric (aqueous enteric coating) is composed of solid or semisolid polymer
spheres of CAP ranging in size from 0.05-3 microns (average particle size of 0.2 microns) .
2. ACRYLATE POLYMERS- Available as 2 forms of enteric acrylic resins- Eudragit L and Eudragit S and the films produced by this are
resistant to gastric fluid and they are soluble in intestinal fluids at pH 6 (Eudragit L) & 7 (Eudragit S). Eudragit L is available as an
organic solution of isopropanol, solid or aqueous dispersion while Eudragit S is available only as an organic solution of isopropanol
and solid.
3. POLYVINYL ACETATE PHTHALATE (PVAP)- it is manufactured by esterification of a partially hydrolysed polyvinyl acetate with
phthalic anhydride. This polymer is similar to Hydroxypropyl Methylcellulose Phthalate HP-55 in stability and pH dependent
solubility. It is supplied as ready to use or disperse enteric systems
4. HPMC PHTHALATE - these are esters of HPMC with phthalic anhydride. These polymers dissolve at a lower pH (5-5.5) than CAP
or acrylic copolymers, and this solubility characteristic may result in higher bioavailability of some specific drugs. These polymers
are quite stable than CAP due to absence of labile acetyl groups.

15. SOLVENTS:-
 The primary function of the solvent system is to dissolve and disperse the polymers and other additives and for
easy application. All major manufacturers of the polymers for tablet coating provide basic physical-chemical
data on their polymers. Some ideal solvent properties are:-
1. It should either dissolve or disperse the polymer system.
2. It should easily disperse other coating solution components into the solvent system.
3. Small concentrations of polymers (2-10%) should not result in an extremely viscous solution (>300cps), creating
processing problems.
4. It should be colourless, tasteless, odourless, inexpensive, nontoxic, inert and non flammable.
5. It should have a rapid drying rate (the ability to coat a 300 kg load in 3-5 hours).
6. It should have no environmental impact.
The widely used solvents either alone or in combination are water, ethanol, methanol, isopropanol, chloroform,
acetone, methyl-ethyl-ketone and methylene chloride. But water is the solvent of choice (due to economical &
environmental factors) also several polymers cannot be applied from aqueous systems. Drugs that readily hydrolyse
in the presence of water can be more effectively coated with non aqueous solvents based coating. But before this
coating initial sealing coat from organic based sub-coating followed by aqueous colour and gloss coating.

16. PLASTICIZERS
 The quality of a film can be modified by the use of “internal” or “external” plasticizing techniques.
 Internal plasticizing pertains to the chemical modifications of the basic polymer that alters the physical
properties of the polymer.
 An external plasticizer can be a non-volatile liquid or any another polymer, which when incorporated with the
primary polymeric film former, changes the flexibility, tensile strength, or adhesion properties of the resulting
film.
 The level of plasticizers ranges from 1-50% by weight of film former.
 Examples are castor oil, propylene glycol, glycerine and surfactants like tweens, spans etc.

17. COLOURANTS continued…….
 It is required to provide the distinct color and elegance to the dosage form.
 To achieve the proper distribution of suspended colorants in the coating solutions it requires the use of fine
powdered colorants with size <10 microns.
 The concentration of colorants in the coating solution depends upon the colour shade, desires type of dye and the
concentration of the opaque extenders.
 For very light shade concentration less than 0.01% id required, while for a dark shade concentration more than
2.0% is required.
 The most common colorants in use are certified by Food Drug and Cosmetics or Drug and Cosmetics colorants.
 There are 2 type of dyes used: LAKE OF DYES & SYNTHETIC DYES.
 Lake dyes are obtained from dyes by precipitating with carriers like alumina/ talc.
 The inorganic materials and the natural colorants are : iron oxides, caramel, carotenoids, turmeric and carmenic
acid.
 There are a variety of products that are commercially available which are- opalux(opaque concentrate for sugar
coating), opaspray(for film coating) an opadry(for complete film coating concentrate)

18. OPAQUE EXTENDERS
 They are very fine inorganic powders used to provide more pastel colours and
increase film coverage. These opaquants can provide a white coating or mask
the colour of the tablet core. Colourants are much more expensive than these
inorganic materials, but less amount of colourants are required when
opaquants are used. Examples include titanium oxide, talc, aluminium
silicate, calcium sulphate, magnesium oxide and aluminium hydroxide.
 Opaque extenders are used to produce opaque films with good hiding power
and film coated tablets with highlighted intagliations.

19. MISCALLANEOUS COATING SOLUTION
COMPONENTS
 These materials provide a dosage form with a unique characteristic by either
providing them special flavours or sweeteners to mask the unpalatable taste
of drugs.
 Surfactants may also be used to solubilize otherwise insoluble ingredients or
to facilitate faster dissolution of the coating.
 Antioxidants are used to stabilize a dye system to oxidation and colour
change.
 Antimicrobials are used to prevent microbial growth in the coating
formulation and during its preparation and storage and on the coating tablet
(because some aqueous coating solutions are particularly prone to microbial
growth and prolonged storage of such composition/ formulation should be
avoided.

20. REFERENCES
1. THE THEORY AND PRACTICE OF INDUSTRIAL PHARMACY by LIEBERMANN &
LACHMANN, 4th EDITION, page no.497-506
2. AULTON’S PHARMACEUTICS- THE DESIGN & MANUFACTURE OF MEDICINES, 4th
EDITION, page no.567-574, 578
3. REMINGTON’S ESSENTIALS OF PHARMACEUTICS, 22nd EDITION, page no. 581-82

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