NTA Level 6 • Semester 1 • PST06103

Tablet Coating

Pharmaceutical Production • Source Session/Topic 19

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Session 19: Tablet Coating

Total Session Time: 120 minutes

Pre-requisites

• None

Learning Tasks

By the end of this session students are expected to be able to:

• Define tablet coating

• List reasons for tablet coating

• Explain types of tablet coating

• Explain equipment for tablet coating

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board and chalk/whiteboard markers

• LCD projector and computer

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Meaning of Tablet Coating (10 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|ASK students to brainstorm on the following question: |

| |

|What is tablet coating? |

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|ALLOW few students to respond |

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|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• Coating is a process by which an essentially dry, outer layer of special

material is applied to the surface of a dosage form in order to confer

specific benefits over uncoated variety

• Tablet coating is the last (optional) critical step in tablet production

cycle and one of the oldest pharmaceutical processes still in existence

STEP 3: Reasons for Tablet Coating (15 minutes)

➢ Coating masks unpleasant odour, taste or colour of the drug

➢ Coating provides physical and chemical protection for the drug

➢ Coating controls the release of drug from the tablet

➢ Coating protects the drug from gastric environment of stomach in case of

acid sensitive drugs

➢ Coating help avoid chemical incompatibility

➢ Coating improves pharmaceutical elegance by using colours and

contrasting printing

STEP 4: Factors Considered in Tablet Coating (10 minutes)

• Tablet properties

o Tablet to be coated must possess the proper physical characteristics

like spherical shape and uniform surface

o Tablets to be coated must be able to tolerate attrition during coating

process i.e. tablets must be resistant to abrasion and chipping

▪ for example, tablet surfaces that are brittle and soften in

presence of heat or affected by coating composition and tend to

become rough in the early stages of coating process are

unacceptable for film coating

• Coating process

o Coating equipment

o Coating parameters

o Facility and ancillary equipment

o Automation of coating process

• Coating composition

o Polymers, colour, plasticizer and solvent

STEP 5: Types of Tablet Coating (35 minutes)

• There three types of tablet coating

o Sugar coating

o Film coating

➢ Non enteric film coating

➢ Enteric film coating

o Other types of coating include compression coating, electrostatic

coating, DIP coating, vacuum film coating, dry coating and laminated

coating

• Sugar Coating

o Sugar coating involves the application of sugar solution with colour

to the tablets for several times to give uniform and elegant film

o Tablets suitable for sugar coating are those;

➢ with deep convex surfaces with thin rounded edges

➢ resistant to breakage, chipping and abrasions (sugar coating

process is long and vigorous)

o Sugar coating involves the following steps;

➢ Sealing

➢ Sub-coating

➢ Syruping (smoothing)

➢ Finishing

➢ Polishing

o Sealing Step

▪ This step prevents penetration of moisture into the tablet core

▪ Over wetting tablets during coating causes moisture to penetrate

the tablet core and lead to softening or disintegration of the

tablet hence affecting physical and chemical stability of the

tablet

▪ Materials used for sealing tablets include shellac (more

effective but lengthens disintegration and dissolution times), zein

(alcohol soluble protein derivative), oleic acid, polyethylene

glycol and alcohol methylene chloride

o Sub-coating Step

▪ Sub coating is applied to form uniform edges and to build up the

tablet size

▪ Sub-coating increases the tablet weight from 50 to 100%

▪ Materials used for sub-coating include gelatin, sugarcane powder,

corn syrup, distilled water, gum acacia

▪ This step involves;

▪ Application of binder solution to the tablets

▪ Dusting of the sub-coating with powders and drying until the

entire tablets have covered and desired thickness is achieved

o Syruping Step

▪ Syruping is done in order to cover the imperfections in the

tablet surface caused during sub-coating step

▪ This step involves;

▪ Application of syrup coating with grossing syrups followed by the

addition of dilute colorants to provide tinted base

▪ Syrup coating constitute colorants, sub-coating powder, calcium

carbonate, cane sugar powder, corn starch, syrup and distilled

water

▪ When the tablets are quit smooth, a syrup solution containing dye

(colouring agent)e is applied until final size and colour are

achieved

▪ Finally a clear syrup coat without dye is applied to the syruped

tablets

o Polishing Step

▪ Polishing is done to obtain the desired lustre to the tablets

▪ Tablets are polished in standard coating pans by application of

carnauba wax (yellow), bees wax (white), paraffin wax or warm

solution of waxes in naphtha or suitable volatile solvents

o Advantages of sugar coating

➢ It prevents unpleasant odour

➢ Gives sweet taste to the tablet by masking any unpleasant or

bitter taste

➢ It is highly elegant and glossed

o Disadvantages of sugar coating

➢ Appreciable increase in size of the tablets

➢ Appreciable increase in weight of the tablets

➢ Tablets cannot be engraved

• Film coating

o Film coating is a process of applying a polymeric solution to tablets

in order to form a thin uniform layer (a film) around the tablet

o Materials used for film coating are classified into;

Non-enteric film formers

▪ They give uniform film with desired mechanical strength

▪ They include Hydroxy propyl methyl cellulose (HPMC), Methyl

hydroxyl ethyl cellulose (HMEC), Ethyl cellulose (EC), Hydroxy

propyl cellulose (HPC), Povidone and acrylate polymers

Enteric film formers

▪ These materials are resistant to gastric acid and they are used

for the following reasons;

▪ to protect acid-labile drugs from gastric fluid e.g. enzymes and

certain antibiotics

▪ to prevent gastric distress or nausea due to irritation from the

drug e.g. sodium salicylate

▪ to deliver drugs intended for local action in the intestines e.g.

intestinal antiseptics

▪ to deliver drugs that are optimally absorbed in the small

intestines to primary absorption site

▪ to proved a delayed-release component for repeat-action tablets

Characteristics of Ideal Enteric Coating Materials

▪ Resistance to gastric fluids

▪ Not susceptible or permeable to intestinal fluids

▪ Compatible with most coating solution components and drug

substances

▪ Stable alone or in coating solution

▪ The film should not change on aging

▪ Should form a continuous film

▪ Should be nontoxic

▪ Should be of low cost

▪ Should be easy to apply without the need of special equipment

▪ Should be readily printed and allow film to be applied to

debussed tablets

▪ Some enteric film formers include cellulose acetate phthalate

(CAP), acrylate polymers, hydroxypropyl methyl cellulose phthalate

(HPMCP), and polyvinyl acetate phthalate (PVAP)

▪ Composition of the solution for film coating

▪ Solvent

▪ For dissolving or disperse the polymers and other additives

to form a coating solution

▪ The solvent should be colourless, tasteless, odourless,

inexpensive, nontoxic, inert, non-flammable and with rapid

drying rate

▪ Examples of solvents are water, ethanol, methylene ethyl

ketone

▪ Plasticizers

▪ they are added to modify the quality of the film (making it

softer, flexible yet strong)

▪ they are of two groups, internal plasticizers and external

plasticizers

▪ level of plasticizers ranges from 1-50% by weight of the

film former

▪ examples plasticizers include castor oil, propylene glycol,

glycerine, surfactants, polysorbate (tween), sorbitan esters

(span), organic acid esters

▪ Colorants

▪ Provide distinct colour and elegance to the tablets

▪ Achieved by proper distribution of suspended colouring

agents in the coating solution

▪ The concentrate of colouring agents in the coating solution

depends on the colour shade (lighter or dark), desired type

of dye and concentration of opaquant extenders

• Colorant used are food, drugs and cosmetic (FD & C) colorants or

drug and cosmetic (D & C) colorants

• They are lakes (dyes precipitated by carriers such as alumina)

and dyes

▪ Opaquant –extenders

• They are very fine inorganic powders used in the coating

solution formulation to provide more pastel colours and increase

film coverage

• They provide white coating or mask the colour of the tablet core

• They include titanium dioxide, silicates e.g. talc, aluminium

silicate; carbonates e.g. magnesium carbonate; sulphates e.g.

calcium sulphate

o Film Defects

▪ Sticking and picking

• Attachment tablets to each other due to over wetting, rapid

drying or tackiness of tablets

• Can be solved by reduce liquid application, control rate of

drying and change of formulations

▪ Roughness

• Formation of rough or gritty surface due to increase in path

length of spray nozzle to tablet bed or rapid drying

• Remedied by decreasing path length and controlling drying rate

▪ Orange peel effect

• Inadequate of spreading coating solution which is caused by

rapid drying, high viscosity of coating solution

• Remedied by decreasing drying rate, decreasing viscosity by

adding solvent

▪ Bridging

• Shrinking or pulling away of film from corners due to over

wetting, less viscous liquids and spread ability problems

• Remedied by decreasing application rate of coating solution,

increasing viscosity and change in formulation

▪ Blistering

• Removal of film due to rapid evaporation of solvent from tablet

core due to rapid evaporation of solvent (high temperature) and

high viscosity of coating solution

• Remedied by decreasing drying temperature, diluting coating

solution

o Advantages of film coating

▪ Causes minimal increase in the size of the tablets

▪ Causes minimal increase in tablet weight

▪ Forms a very thin layer over tablets

▪ Engravings are possible on tablets surface (not possible in sugar

coating)

▪ Provides better mechanical strength to the tablets

▪ The cost is less

STEP 6: Equipment for Tablet Coating (35 minutes)

• Standard Coating Pan

o Also known as conventional pan system

o Consists of a circular metal pan mounted angularly on a stand

o The pan rotates on its horizontal axis by a motor

o Heated air is directed into the pan and on the tablet bed surface and

is exhausted by means of ducts through the front of the pan

o Coating solution is applied to the tablets by ladling or spraying the

material on to the rotating tablet bed

o Spraying system is advantageous over the ladling system

▪ It is faster and provides more even distribution of the coating

solution or suspension than ladling

▪ It reduces drying time between solution application in sugar

coating

▪ It allows continuous application of coating solution in film

coating

▪ In the standard coating pan, drying efficiency is improved by;

• Pellegrini pan

o A baffled pan that diffuses or distributes the drying air

uniformly over the tablet bed surface

• Immersion sword

o A perforated metal sword device immersed in the tablet bed

(in the pan)

o Drying air is introduced through this device and flows upward

from the sword through the tablet be

• Immersion tube system

o A tube immersed in the tablet bed to deliver heated air

o The coating solution is applied with the heated air from the

immersed tube

• Perforated Coating Pan

o Employs a perforated or partially perforated drum

o The drum rotates on its horizontal axis in an enclosed housing

o The coating solution is applied to the surface of the rotating bed of

tablets through spraying nozzles, which are present inside the drum

o Perforated pan coaters are efficient drying system with high coating

capacity

Types of perforated pan system are, Accela-cota system, Hi coater

system, Dria coater pan and the Glatt coater (which is the

largest coater)

▪ Accela-coater and Hi coater systems; -drying air is directed into

the drum, passed through the tablet bed and exhausted through

perforations in the drum

▪ Dria coater pan; -drying air enters through hollow perforated

ribs located on the inside periphery of the drum

• As the coating pan rotates, the ribs dip into the tablet bed and

drying air passes up through.

• Exhaust is from the back of the pan

▪ Glatt coater

• Drying air can be directed from inside the drum through the

tablet bed

• The air is exhausted through an exhaust duct

• Fluidized bed Coater

o In this system, fluidization of tablet mass is achieved in a columnar

chamber by an upward flow of drying air

o The air flow is controlled so that more air enters the centre of the

column causing the tablets to rise in the centre (fluidization)

o The movement of tablets is upward through the centre of the chamber,

then fall toward the chamber wall, finally moving downwards to re-

enter the air stream at the bottom of the chamber

o Coating solution is applied from a spray nozzle which is located at

the bottom of the chamber

o In other models of fluidized bed coater, the coating solution is

sprayed on the top of the cascading tablet bed by nozzles located in

the upper region of the chamber

STEP 7: Key Points (5 minutes)

• Coating is one of the important technique in manufacturing of dosage

forms

• Coating improves the stability, shelf life and release pattern of drugs

from tablets

• Coating of tablets help improve patient compliance

• Tablet coating is the last (optional) critical step in tablet production

cycle and one of the oldest pharmaceutical processes still in existence

• There three main types of tablet coating; sugar coating film coating

(Non enteric or enteric film coating)

• Equipment commonly used for coating include standard coating pan,

perforated coating pan and fluidized bed coater

STEP 8: Evaluation (5 minutes)

• What is tablet coating?

• What is sugar coating?

• What is the difference between film coating and sugar coating?

References

Aulton M.E & Kevin M.G, Eds: (2013) Pharmaceutics: The design and

manufacture of medicines, (4th ed.) Churchill Livingstone

Hugo and Russell (2011), Pharmaceutical Microbiology (8th ed.), Willey-

Blackwel publications

Gennaro, R. A, et al. (Eds) (1995) Remington: The Science and Practice of

Pharmacy, Volume I & II, (19th ed.): Mack Publishing Company, Easton,

Pennsylvania 18042

Liebsch, B et al. (1988): Tanzania Pharmaceutical Handbook, Dar es Salaam

University Press.

Lund, W. Editor (1994). The Pharmaceutical Codex, Principles and Practice

of Pharmaceutics (12th ed.): The Pharmaceutical Press, London

Polderman, J. (1990) Introduction to Pharmaceutical Production: Novib, The

Hague

Rawlins E.A, Editor: (1977) Bentley’s Textbook of Pharmaceutics, (8th ed.)

Baillie're Tindall. London Kamm, G. and Kohler, B. Editors: (1995)

Manual for Decentralized Infusion Production, Infusion Unit Project

Tanzania

Schmidt, O. (Eds) (2000) Pharmaceutical Quality systems, Interpharm Press,

Colorado.

Shayne C et al. (2008), Pharmaceutical Manufacturing Handbook: Production

and processes, John Wiley & Sons

Watson, D. G (1999) Pharmaceutical Analysis: A Textbook for Pharmacy

Students and Pharmaceutical Chemists: Churchill Livingstone,

Edinburgh.

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