Tablet Coating NSU1.ppt

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TABLET COATING

Dr. Mohammad

Shariare

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Tablet Coating

 Tablet coating is the application of a coating

material to the exterior of a tablet with the intention of conferring benefits and properties to the dosage form over the uncoated variety.

 The application of coating to tablets, which is

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Tablet Coating Principles

 _{The decision to coat a tablet for one or more of the following}

objectives:

1. To mask the taste, odor or color of the drug

2. To provide physical and chemical protection for the drug

3. To control the release of the drug from the tablet

4. To protect the drug from the gastric environment of the stomach with an acid resistant enteric coating.

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Tablet Coating Principles

6. To improve the pharmaceutical elegance by use of special colors and contrasting printing. 7. Colored coatings aid in the rapid

identification of product by the manufacturer, the dispensing pharmacist and the patient.

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Primary components

involved in Tablet Coating

 Tablet properties – physical characteristics  Coating

process- Design and control of coating equipments –

 _{A coating pan}

 _{A spraying system}  _{An air handling unit}  _{A dust collector}

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Types of Tablet Coating

 Two main types are in use:

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Film Coating

 Film coating involves the deposition, usually by a spray

method, of a thin film of polymer surrounding the tablet core.

 _{The coating liquid (solution or suspension) contains a}

polymer in a suitable liquid medium together with other ingredients such as pigments and plasticizers.

 This solution is sprayed on to a rotating, mixed tablet bed or

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Film and Sugar Coating

Nearly all newly launched coated products are film coated rather than sugar coated, for the reasons

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Film Coating

 Materials used in Film Coating:

 Polymer  Plasticizer  Colorants  Solvent

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Ideal characteristics of a film

coating material

 _{Solubility in solvent of choice for coating preparation.}

 Solubility required for the intended use e.g. free

water solubility, slow water solubility, pH-dependent solubility (enteric coating).

 Capacity to produce an elegant looking product.

 _{Stability in the presence of heat, light, moisture, air}

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Ideal characteristics of a film

coating material

 _{Essentially, no color, taste or odor.}

 _{Compatibility with common coating solution} additives.

 Nontoxicity with no pharmacologic activity and ease of application to the particles or tablets.

 Resistance to cracking and provision of adequate moisture, light odor sublimation barrier when

desired.

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POLYMER:

Ideal properties of film coating polymer:

SOLUBILITY _{High water solubility is desired for}

normal polymers. Low water solubility may be required for modified release polymers.

VISCOSITY _{Low viscosity of the polymeric}

solution is required for trouble free processing.

PERMEABILITY _{Polymers should have low}

permeability against water vapor or oxygen if environmental protection is desirable.

MECHANICAL

PROPERTIES Adequate strength should be _{present to withstand the stresses}

encountered during normal

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Types of Film Formers or

Polymers

 Nonenteric materials:

 Hydroxypropyl methyl cellulose  Methyl hydroxyethylcellulose  Ethylcellulose

 Hydroxypropylcellulose  Povidone

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Solvents

 The primary function of a solvent system is to dissolve or disperse polymers and other additives and convey them to the substrate surface.

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 Solvents or solvent blends for polymer can be selected according to several criteria:

1.Empirically

2.According to general rule “ like dissolve

like”

3.Quantitatively according to solubility

parameters

4.Qualitatively based upon assessment of the

intermolecular forces

Solvents

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Solvents

 Characteristics of an ideal solvent system:

 It should either dissolve or disperse the polymer

system.

 It should easily disperse other coating

components into the solvent system.

 Small concentration of the polymer should not

result in an extremely viscous solvent system creating processing problems.

 It should be colorless, tasteless, inert and

non-inflammable.

 It should have a rapid drying rate.

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Plasticizers

 _{Plasticizers are generally added to film coating formulations to}

modify the physical properties of the polymer to make it more usable.

 _{As the solvent is removed most polymeric materials tend to}

pack together in three dimensional honeycomb arrangements.

 _{The choice of plasticizers depends upon the ability of}

plasticizer material to solvate the polymer and alter the polymer-polymer interactions.

 _{When used in correct proportion to the polymer these}

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Properties of plasticizer:  Colorless

 Odorless

 Non-volatile

 Thermally stable  Water resistant

 Chemically resistant

 Non-migrating in film and  Physiologically inert

Plasticizers

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Reason for adding plasticizer:  Reduce brittleness

 Improve flow

 Improve flexibility

 Increase toughness and tear resistance to a film

Plasticizers

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Plasticizers

Effect of plasticizers on the properties of film coating:

Property Effect of increasing plasticizer concentration Tensile strength Decreased Elastic modulus Decreased Film adhesion

May increase but vary

Solution viscosity

Increased but magnitude of the effect depend on the molecular

weight of plasticizer Film

permeability

Can increase or decrease depend on chemical nature of plasticizer Glass

transition temperature

Decreased but magnitude of effect depend on compatibility with

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Plasticizers

Examples of plasticizers include:

 Polyhydric alcohols: polyethylene glycol,

glycerol, propylene glycol

 _{Acetate esters: Triethyl citrate}

 Phthalate esters: such as diethyl phthalate  Oils/glycerides, such as castor coconut oil  Surfactants such as polysorbates (Tweens),

sorbitan esters (Spans)

 The polymer and the plasticizer must be at least

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Colorants

 Colorants are used to provide distinctive color and

elegance to a dosage form.

 Color variation is readily detected by pharmacist and

patients.

 Colors must be reproducible and stable.  Dyes or Lakes can be used.

 Concentrations may vary from 0.01% to 2%.

Examples of colourants are: • iron oxide pigments

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Opaquant-extenders

 These are very fine inorganic powders used in coating solution formulations to provide more pastel colors and increase film

coverage.

 These opaquants can provide a white

coating or mask the color of the tablet core.  Less colorants need to be used when

opaquants are used.

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Miscellaneous Coating

Solution Components

 Flavors or sweeteners can be added to mask

objectionable odor or to enhance a desired taste.

 Surfactants can be used to solubilize

insoluble ingredients or to facilitate faster dissolution of the coating.

 Antioxidants can be added to stabilize a dye

system to oxidation and color change.

 Antimicrobials can be added to prevent

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Film Coating Process

 Two methods are available:

1. Pan-Pour methods:

 The coating solutions are poured over the tablet cores.  _{The operator determines the quantity of solution to}

add, the method and rate of the pouring, when to

apply drying air and how long or how fast the tablets should be tumbled in the pan.

 Tablets coated by pan pour methods are subjected to

alternate solution application, mixing and drying steps.

 _{This method is relatively slow and relies heavily on the}

skills and technique of the operator to balance the steps to produce an acceptable product.

 Tablets that are coated by pan pour method almost

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Film Coating Process

2. Pan Spray method

 The introduction of spraying equipment has

improved the coating efficiency process.

 Spraying allows for automated control of

liquid application.

 Spray patterns are selected to provide a

continuous and across the tablet bed surface.

 Broad, flat spray patterns are usually chosen

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Process details

 The vast majority of film-coated tablets are produced by a process which involves the atomization (spraying) of the coating

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Process details

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Basic process requirements for

film coating

1. Adequate means of atomizing the spray liquid for

application to the tablet cores.

2. Adequate mixing and agitation of the tablet bed.

3. Sufficient heat input in the form of drying air to

Provide the latent heat of evaporation of the solvent.

4. Good exhaust facilities to remove dust- and

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Mechanism of film coating

 Spray coating solution  Droplet formation

 Impingement on the solid body of tablet  Wetting tablet surface

 Spreading of polymer matrix

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Coating faults

These arise from two distinct causes:

1. Processing: for example, inadequate drying conditions will permit coating previously deposited on the tablet surface to stick against neighbouring tablets. When parted, this will reveal the original core surface underneath.

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Ideal characteristics of

film-coated tablets

coated tablets

 _{Film-coated tablets should display an even coverage of}

film and colour.

 no abrasion 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}

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Types of Film Formers or

Polymers

 Enteric materials:

 Cellulose acetate phthalate

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Reasons for Enteric

Coating

 To protect acid labile drugs from the gastric

fluid. Eg. Certain antibiotics.

 To prevent gastric distress or nausea due to

irritation from a drug. E.g sodium salicylate.

 To deliver drugs intended for local action in

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Reasons for Enteric

Coating

 To deliver drugs that are optimally

absorbed in the small intestine to their primary absorption site in their most concentrated form.

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Enteric Coating

 An ideal enteric coating material should

have the following properties:

 _{Resistance to gastric fluids}

 Ready susceptibility to or permeability to intestinal

fluids.

 Compatibility with most coating solution

components and the drug substrates.

 _{Stability alone and in coating solutions.}

 Formation of a continuous (uninterrupted) film.  Low cost