Tablet coating

322 322 PHTPHT

Nahla Barakat, PhD

King Saud UniversityCollege of Pharmacy

1432/2011

1

04/19/23322 PHT

Coated tablets are defined as “tablets covered with one or more layers of mixture of various substances such as natural or synthetic resins, gums , inactive and insoluble filler, sugar, plasticizer, polyhydric alcohol ,waxes ,authorized colouring material and sometimes flavoring material .

Coating may also contain active ingredient.

Substances used for coating are usually applied as solution or suspension under conditions where vehicle evaporates.

2

04/19/23

322 PHT

Aspects of tablet coating

1. Therapy i) Avoid irritation of esophagus and stomach ii) Avoid bad taste iii) Avoid inactivation of drug in the stomach iv) Improve drug effectiveness v) Prolong dosing interval vi) Improve dosing interval vii) Improve patient compliance

3

04/19/23322 PHT

2. Technology

i) Reduce influence of moisture ii) Avoid dust formation iii) Reduce influence of atmosphere iv) Improve drug stability v) Prolong shelve life 3. Marketing i) Avoid bad taste ii) Improve product identity iii) Improve appearance and acceptability

4

04/19/23322 PHT

KEY FACTORS: TABLET PROPERTIES - Shape - Tolerance - Surface area COATING PROCESS - Equipments - Parameters - Facility and

equipment - Automation COATING COMPOSITION - Polymers -

Solvents - Plasticizers - Colorants

5

04/19/23322 PHT

Evaluation criteria for pre-formulated coating systems

Film strength and flexibility Film adhesion Hiding power/opacity Colour uniformity Gloss Ease of use

6

04/19/23322 PHT

Types of coating processes

Three main types are used in the pharmaceutical industry today;

- Film coating - Sugar coating - Compression coating

7

04/19/23322 PHT

Spray Coater

Coating pan

8

04/19/23322 PHT

Tablet coating machine9

04/19/23322 PHT

Film Coating

Film coating (the most popular today): 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.

10

04/19/23322 PHT

Film Coating: Appearance Dust elimination Taste masking Odour masking Isolation Protection Drug release

11

04/19/23322 PHT

Accela cota is the prototype of perforated cylindrical drum providing high drying air capacity.

Fluidized bed coating, very hard tablets (hardness > 20 N) have to be used

12

04/19/23322 PHT

Types of film coating: Immediate release Modified release

13

04/19/23322 PHT

Ideal characters of coating material

Solubility in the coating solution Solubility required for intended use- Free water solubility, Slow water

solubility, pH- dependent solubility Capacity to produce elegant looking product Stability in presence of water, heat, moisture, air, and substrate being

coated and no change in properties with aging. Essentially no color, odor, or taste Compatibility with common coating solution additives Nontoxic and ease of application Resistance to cracking and should act as barrier No bridging or filling of the debossed tablet surfaces by the film former Ease of printing procedure on high-speed equipment Low cost & Ease of application without specialized equipment

14

04/19/23322 PHT

Materials used in film coating

Film coating formulation (Composition of the coating liquid)

1- Polymer 2- Plasticizer 3- Colorants 4- Solvent (vehicle): Examples: water,

ethanol, methanol, isopropranol, chloroform, acetone, methylethyl ketone, and methylene chloride

15

04/19/23322 PHT

Polymers for film coating

Immediate release coating polymers

Modified release coating polymers

1- Cellulose derivativesEx: HPMC

Extended release coating polymers

Enteric coating polymers

It is readily soluble in aqueous mediaForm film with good mechanical properties(strength, flexibility and adhesion to the tablet coreOther examples: MC, HPC

They are dissolved in organic solvent or dispersed in aqueous medium1- Cellulose derivativesEx: Ethyl cellulose

1- Methacrylic acid copolymers:Eudragitthey are insoluble in water at low pH (stomach) but gradually soluble as pH rises towards neutrality (small intestine)

2- vinyl derivatives:PVP, it has a limited use in film coating because of its inherent tackiness.Copolymer of PVP and vinyl acetate forms better filmsPVPVA copolymer

2- Phthalate esters:e.g. Cellulose acetate phthalate (CAP)

16

04/19/23322 PHT

plasticizer

Combination of plasticizer may be used to get desired effect Concentration of Plasticizer Expressed As The amount of polymer being

plasticized. Recommended Level of Plasticizer : 1 to 50% by weight of the film former.

EXAMPLES : Castor oil; Polyethylene glycol of 200 and 400 series; surfactants eg; Tweens; Spans; organic acid esters. water- soluble plasticizer : PEG, propylene glycol. organic- soluble plasticizer : castor-oil and Spans.

17

04/19/23322 PHT

COLORANTS

Colorants may be soluble in the solvent system or suspended as insoluble powders.

Used to provide distinctive color and elegance to a dosage form.

To achieve proper distribution of suspended colorants in the coating solutions requires the use of fine-powdered colorants (< 10 microns ).

Most of colorants are synthetic Dyes or Lakes of Dyes approved by the FD&C and D&C.

18

04/19/23322 PHT

LAKES :

Examples Inorganic materials: iron oxides Natural coloring materials :Anthocyanins, caramel, carotenoids,

chlorophyll, indigo, flavones, and carminic acid. Various concentrates promoted as achieving less lot-to-lot color

variation Opalux – Opaquant color concentrate for sugar coating. Opaspray- Opaque color concentrate for film coating. Opadry – Complete film coating concentrate

19

04/19/23322 PHT

OPAQUANT-EXTENDERS These are very fine inorganic powders used in the

coating solution formulation to provide more pastel colors and increase film coverage.

Opaquant provides a white coating or mask the color of the tablet core, and thus the less amount of the colorants are required.

Examples: Silicates (talc, aluminium silicate); Carbonates (magnesium carbonate); Sulfates (calcium sulfate); Oxides (Mg oxides, titanum oxide)

20

04/19/23322 PHT

ENTERIC COATING

The technique involved in enteric coating is protection of the tablet core from disintegration in the acidic environment of the stomach by employing pH sensitive polymer, which swell or solubilize in response to an increase in pH to release the drug.

Aims of Enteric protection: To mask taste or odour Protection of active ingredients, from the acidic

environment of the stomach. Protection from local irritation of the stomach mucosa. Release of active ingredient in specific target area

within gastrointestinal tract.

21

04/19/23322 PHT

Examples of enteric coated OTC products : Examples of enteric coated OTC products

Enteric coated aspirin E.g. Micropirin® 75mg EC tablets Enteric coated peppermint oil E.g. Colpermin®

22

04/19/23322 PHT

Sugar coating

Compressed tablets may be coated with colored or uncolored sugar layer. The coating is water soluble and quickly dissolves after swallowing.

The sugarcoat protects the enclosed drug from the environment and provides a barrier to objectionable taste or order.

The sugar coat also enhances the appearance of the compressed tablet and permit imprinting manufacturing’s information.

Sugar coating provides a combination of insulation, taste masking, smoothing the tablet core, colouring and modified release.

The disadvantages of sugar coating are the time and expertise required in the coating process and thus increases size, weight and shipping costs.

23

04/19/23322 PHT

Typically, tablets are sugar coated by panning technique, using traditional rotating sugar-coating pan with a supply of drying air (thermostatically controlled).

The pan is automatically rotated, allowing tablets to tumble over each other while making contact with the coating solutions which are gently poured or sprayed, portion wise onto the tablets with warm air blown to hasten drying.

Each coat is applied only after the previous coat is dried.

24

04/19/23322 PHT

Composition of sugar coat

Seal coating Sub coating Syrup coating Color coating Polishing printing

25

04/19/23322 PHT

Sealing 1- Sealing (Waterproofing)

This involved the application of one or more coats of a waterproofing substance in the form of alcoholic spray, such as pharmaceutical Shellac (traditionally) or synthetic polymers, such as CAP.

( Unless a modified-release feature needs to be introduced, the amount of the sealing coat applied should be carefully calculated so that there is no negative effect on the drug release characteristics in case of immediate release product.)

(WHY Sealing?) a- Sugar-coatings are aqueous formulations which allow water to penetrate directly

into the tablet core and thus potentially affecting product stability and possibly causing premature tablet disintegration.

b- Application of many coats of partially or completely water-insoluble polymers in this step, enables sugar-coated product to exhibit modified-release pattern (extended release or delayed "enteric“-release characteristics).

26

04/19/23322 PHT

2- Subcoating

-Large quantities of sugar-coatings are usually applied to the tablet core (typically increasing the tablet weight by( 50- 100%)- WHY?- In order to round off the tablet edge. Much of this material build-up occurs during this stage and is achieved by adding a bulking agent such as Calcium carbonate, to the sucrose solution. - Antiadherents e.g. Talc may be added after partial drying to prevent sticking of the tablets together.

27

04/19/23322 PHT

3- Smoothing

The subcoating stage results in tablets with rough surfaces. To facilitate the color application (which requires smooth surface), subcoated tablets are smoothed out by a thick sucrose syrup coating. 4- Coloring Color coatings usually consist of thin sucrose syrup containing the requisite coloring materials. (water-soluble dyes or water-insoluble pigments may be used) This step must be done into a clean pan deprived of any residues from the previous operations

28

04/19/23322 PHT

5- Polishing After the coloring step, the tablet surfaces tend to be smooth but somewhat dull in appearance. To achieve glossy finish, final stage involving application of waxes (beeswax carnuba wax) is employed.

6- Printing Different tablets could be identified by manufacturer' logo, product name, dosage strength or other appropriate code.For sugar-coated tablets, such identification could be only achieved by printing process using special edible inks

29

04/19/23322 PHT

Example of sugar coated tablets Brufen® POM Available in 200mg and 400mg strength

Premarin® POM Conjugated oestrogens 625mcg (maroon) and 1.25mcg (yellow)

Colofac ® P Mebeverine hydrochloride 100mg Round, white, sugar coated

Kalms ® GSL 45mg Hops powder,90mg Gentian powdered extract, and 135mg Valerian powdered extract

30

04/19/23322 PHT

The constituents of coating solution used for sugar coating

Seal coating Sub coating Syrup coating Polishing solution

Zein/shellac Gelaatin colorant Carnauba wax

Oleic acid Acacia Sub coating powder

beeswax

Propylene glycol

Sugar cane powder

Cal. carbonate Paraffin wax

PEG 4000 Corn syrup Sugar cane powder

Naphtha

Methylene chloride

Syrup Corn starch

Alcohol Distilled water syrup

Distilled water

31

04/19/23322 PHT

Summary of polymers used as coating solution

polymer Trade name Application

Shellac EM Coat 120 NMarcoat 125

Enteric coatingsTaste/odor masking

Cellulose acetate Aquacoat CPDSepifilm LPKlucelAquacoat ECDMetolose

Enteric coatingsTaste maskingSustained release coatingSub coat moisture and barrier sealant pellet coating

Polyvinylacetate phthalate

Sureteric Enteric coating

methylacrylate Eudragit Enteric coatingsSustained release coatingsTaste maskingMoisture protectionRapidly disintegrating films

32

04/19/23322 PHT

TABLE. Comparison between Film coat and Sugar coat Features Film Coating Sugar coating

Tablet:Appearance  Weight increase because of coating material Logo or ‘break lines

Retain contour of original core.  Usually not as shiny as sugar coat type

2-3%

Possible

Rounded with high degree of polish

30-50%

Not possible

ProcessOperator training required  Adaptability to GMP Process stages Functional coatings

Process tends itself to automation and easy training of operator High Usually single stage Easily adaptable for controlled release

Considerable  

 Difficulty may arise

 Multistage process

 Not usually possible apart from enteric coating

33

Compression-coating of tablets

Although less popular, it gained increased interest in recent years for creating modified-released products involves the compaction of granular materials around preformed tablet core using specially designed tableting equipment. Compression coating is a dry process

34

04/19/23322 PHT

After tablet core manufacture, it is transferred (centrally positioned) to another slightly larger die that is partially filled with the coating powder. More coating powder is filled on the top of the core and compressed again resulting in tablet within tablet.

35

04/19/23322 PHT

Why Compression coating

Mostly, the coat is water soluble and disintegrate easily after swallowing, in order to achieve immediate-release product

1- traditionlayy, to separate incompatible materials

(one in the core, the other in the coat). There is an interface between the two layers and thus compromize product stability.

2- May be used to create modified relaese products

36

04/19/23322 PHT

SPECIALIZED COATING TECHNIQUICS Dip-coating In this, cores to be coated are a held in a suitable

device eg: baskets Dipped into coating solution and then dried taking

care to prevent adherence to one another. For obtaining more perfect or heavier coats the

dipping and drying steps may be repeated several times one after another.

Several dipping arrangements are obtainable, amongst them the sophisticated devices comprise tiny suction tubes, which hold the individual tablets apart until drying is accomplished.

Before proceeding to coat additional tablets or begin recoating cycles.

37

04/19/23322 PHT

LAMINATED-COATING Laminated coating provides multiple layers for

incorporation of medicament; for example Repeat-action tablet, here a portion of the

drug is kept in outer lamella or coating Enteric tablet, here one drug could be made

available for gastric absorption while another for release in intestine

Buccal-swallow tablet, this could first be administered sublingually, and upon a signal, such as release of flavour from the inner core, the same may be swallowed as a normal peroral tablet.

38

04/19/23322 PHT

Dry coating It avoids the use of water or, at least, allows it

to be reduced to very small amounts with respect to the coating material, thus overcoming the need for time- and energy-consuming drying phases, as well as possible drug stability issues.

In this technology, powdered coating materials are directly coated onto solid dosage forms without using any solvent, and then heated and cured to form a coat.

39

04/19/23322 PHT

Coating defects

Since spraying, coating distribution, and drying take place at the same time, tablet coating is a dynamic, complex

process that is affected by many variables. In no particularorder, here are some of the parameters that you should check when evaluating your coating operation to determine the source of defective coated tablets.

Many problems occur in coating when youcan’t control every important parameter, such as

temperature, pan pressure, spray rates, and atomization pressure.

40

04/19/23322 PHT

Picking and sticking.

This is when the coating removes a piece of the tablet from the core. It is caused by over-wetting the tablets, by under-drying, or by poor tablet quality.

41

04/19/23322 PHT

Bridging. This occurs when the coating fills in the lettering or logo on the tablet and is typically caused by improper application of the solution, poor design of the tablet

embossing, high coating viscosity, high percentage of solids in the solution, or improper atomization pressure.

42

04/19/23322 PHT

Capping. This is when the tablet separates in laminar

fashion. The problem stems from improper tablet

compression, but it may not reveal itself until you start coating.

Be careful not to over-dry the tablets in the preheating stage. That can make the tablets brittle and promote capping.

43

04/19/23322 PHT

Twinning. This is the term for two tablets that stick together, and it’s a common problem with capsuleshaped tablets. Assuming you don’t wish to change the tablet shape, you can solve this problem by balancing the pan speed and spray rate. Try

reducing the spray rate or increasing the pan speed.

44

04/19/23322 PHT

Mottled color. This can happen when the coating solution is improperly prepared, the actual spray rate differs from the target rate, the tablet cores are cold, or the drying rate is out of spec.

45

04/19/23322 PHT

Orange peel. This refers to a coating texture that resembles the surface of an orange. It is usually the result of high atomization pressure in combination with spray rates that are too high.

46

04/19/23322 PHT

attribute the peeling in this photo to excessive moisture within the tablet, which prevented the coating from adhering. However, the tablet coating also pulled the granulation out of the tablet, a picking defect. That is usually caused by over-wetting the tablet or by a tablet that is

47

04/19/23322 PHT

This photo shows a very porous tablet that prevented the coating from adhering to the surface. These tablets should have been coated longer, and the atomization pressure should have been reduced to decrease the slight orange peel, or textured, surface.

48

04/19/23322 PHT

This photo shows multiple defects. The initial problem was erosion of the tablet edge due to a soft or friable tablet or because the pan was turning too fast or both. Peeling and breakage also appear here.

49

04/19/23322 PHT

Just one broken tablet can distribute particles to all the other tablets and mar their appearance.These tablets likely broke because they had poor hardness.

50

04/19/23322 PHT