CHAPTER 8: SOLID DOSAGE FORM COATING TECHNOLOGYNOOR MUHAMMAD SYAHRIN BIN YAHYAINTRODUCTION

INTRODUCTION

› Coating technology is used extensively in the pharmaceutical industry, e.g. for the application of non-functional or functional coats (aesthetic, protective or rate controlling polymer films) and for the deposition of Active Pharmaceutical Ingredients (APIs) onto nonpareils (multi-particulate dosage forms).

› In addition to efficient techniques for API layering of multi particulate systems, an accurate method of coating objects 3 to 30 mm in length with APIs is also desired in the pharmaceutical industry as this is the size range of most single-unit solid dosage forms.

› These include tablets for oral administration and forms for other methods of delivery including human implantation. Existing methods of coating objects in this size range have limitations, e.g. in terms of coating speed and accuracy/uniformity, particularly for the deposition of low dose API onto single unit tablet dosage forms which requires a greater degree of accuracy than can be achieved using current tablet coating techniques.

LEARNING OUTCOMES

› After completing this unit, student should be able to:

1. Understand the equipment's requirement in coating process

2. Understand the types of coating

3. Understand the quality control aspects in coating process

CHAPTER 8: SOLID DOSAGE FORM COATING TECHNOLOGY8.1: EQUIPMENT REQUIREMENTS

EQUIPMENT REQUIREMENTS

Conventional coating pan

The perforated coating pan

The fluidized bed coater (air

suspension)

EQUIPMENT REQUIREMENTS

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.

The perforated coating pan

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

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.

Conventional coating pan

Application & Process:

Conventional coating machine are used to sugar coat tablets, pills, etc in for a variety ofindustries such as Pharmaceutical, Confectionery, Food and others. They are also used forrolling and heating beans and edible nuts or seeds.

The products is to be filled inside the pan. During the rotation motion, coating material issprayed by spraying system according to the technological process and rational technologicalprocess. So process materials (product) are coated due to rotating pan. The coating roundpot is rotated by variable speed. At the same time hot air is supplied through inbuilt hot airblower system which dries rapidly (heating or cooling and evenly thus forming a solid andsmooth surface.

The perforated coating pan› Perforated or partially perforated drum

› Rotated on its horizontal axis in an enclosed housing

› The coting solution is applied to the surface of the rotating bed of tablets through spraying nozzles, which are present inside the drum

› Perforated pan coaters are efficient drying systems with high coating capacity

Accela-cota

Hi-Coater system

Diracoater

The Glattcoater

Accela-cota Pan › Pan is fully perforated.

› Contain mixing blades.

› Inlet air is by a plenum in contact with the top of the pan.

› Air is exhausted by a plenum located below the pan.

Hi-Coater system Diracoater Pan› Consists of four perforated

segments which are perpendicular to each other.

› Each of these perforations acts as an opening for air outlet which is fixed to the exterior of the pan surface.

› Drying air is introduced into pan through an opening located on inside periphery of top of the pan.

The Glatt Coater Pan

› Similar to that of accela-cota.

› A divided air plenum located beneath the moving tablet bed enables air to be blown into or exhausted from the pan through either or both of the two sections.

› In addition, another air plenum, connected to an opening above the door (similar to that in hicoater also allows air to be blown into open) exhausted from the pan.

› Quite expensive.

› Drying air directed from inside the drum through bed and out an exhaust duct.

› Several air flow configurations are possible.

The Fluidized Bed Coater Pan

CHAPTER 8: SOLID DOSAGE FORM COATING TECHNOLOGY8.2: TYPE OF COATING

Type of Coating

› There are several types of coating such as:

Enteric coating

Functional coating

Protective coatings

Protective coatings› Protective coating is thin films of water

soluble polymers are often applied for taste or odour masking, to improve the stability of moisture sensitive products or for better mechanical resistance of the product during handling.

› Such protective coatings need to remain intact for the short time of swallowing the dosage form. Thereafter they should dissolve instantaneously to assure immediate drug release without retardation.

› Polymers employed for these tasks are mostly water-soluble, such as cellulose ethers (e.g. hydroxypropylmethylcellulose (HPMC)), polyvinyl acetate (PVA) or polyvinyl pyrrolidone(PVP).

› Eudragit® E is a methacrylic copolymer especially designed to be insoluble in the saliva, but should rapidly dissolve in the acidic pH of the stomach.

› Sometimes also enteric polymers, e.g. shellac are applied at very low coating level. In that case the film thickness is not sufficient to provide gastric resistance and disintegrated in the stomach within 30 min

taste or odor masking

to improve the stability of moisture sensitive products

for better mechanical resistance of the product during handling

Functional coatings

› Film coatings, which are applied to achieve a certain desired release profile of the incorporated drug, are generally called functional or modified-release coatings.

› Those, intended to protect the drug from the acidic environment of the gastric medium or to prevent the drug release in this part of the GIT, are commonly called enteric coatings.

› Extended release coatings, in contrast, are requested to control the release of the drug over a prolonged period of time.

intended to protect the drug from the acidic environment of the gastric medium

to prevent the drug release in this part of the GIT

are requested to control the release of the drug over a prolonged period of time

Enteric coatings› Enteric coatings are prepared from

gastric resistant polymers. The coatings prepared from such polymers remain intact in acidic environment, but dissolve readily at the elevated pH of the small intestine. This property is related to the chemical structure of the applied polymer.

› The most effective enteric polymers contain many carboxylic acid groups with a pKa of 3-5.

› Therefore they will dissociate and dissolve only when the pH rises above this value. Before the synthetic polymers were introduced to the market, shellac, a natural polymer, was one of the main polymers used for this purpose.

› Cellulose acetatephthalate (CAP) was the first synthetic polymer described in 1937, which gained soon high popularity as a gastric resistant polymer.

prepared from such polymers remain intact in acidic environment

dissolve readily at the elevated pH of the small intestine

related to the chemical structure of the applied polymer.

CHAPTER 8: SOLID DOSAGE FORM COATING TECHNOLOGY8.3: SUGAR COATING

Sugar Coating

› A sugar coating is basically is a thick, hard coating of sugar surrounding the tablet. It is no different in design to the sugar coatings placed on Smarties® or Minstrels ®. This is a traditional method used to hide the flavour of particularly unpleasant tasting drugs e.g. ibuprofen and quinine, both of which are very bitter. The other advantage of a sugar coating is that it can prevent light or moisture from entering the tablet, which causes the drug to break down too quickly.

› Due to the increase in tablet size caused by sugar coating, drug manufacturers have largely changed to using 'film coatings'. These are very thin layers of a safe ingredient placed around the tablet to again protect the tongue from the flavour of the contents and protect the contents from moisture and light. The film will break down with agitation and significant amounts of moisture (saliva or stomach acid) and therefore does not significantly affect the way in which the drug is absorbed into the body.

› Crushing these tablets therefore may not seriously effect how the drug is released but may cause the resultant mixture to be unpleasant to taste.

Stage of Sugar Coating

Tablet Sealing coatSub coat –

round off edges

Smoothing coat – adds bulk to

the tablet. Contains

colorants where applicable

Advantages Sugar Coating

It utilizes inexpensive and readily available raw materials.

No complex equipment or services are required.

The process is capable of being controlled and documented to meet modern GMP standards.

For high humidity climates, it generally offers a stability advantage over film coated tablets.

CHAPTER 8: SOLID DOSAGE FORM COATING TECHNOLOGY8.4: FILM COATING

Film Coating

› Film coating of solid dosage forms is a high sophisticated process, first described in 1930.

› Its obvious advantages resulted in a soon replacement of the traditional sugar coating by the emerging technology, thus the first film-coated tablet became commercially available in 1954.

› The technology advanced with the introduction of the semi-synthetic cellulose derivatives and the synthetic acrylic polymers in the early 1950s.

Film coatings are applied for several

reasons

Taste masking and moisture- / light protecting

coatings

Improved product

appearance

Improved mechanical

resistance of the coated product (e.g. Reduced

friability)

Modified drug release (e.g.

Gastric resistant or extended

release coatings)

Film Coating

› A film coating is a thin polymer-based coat applied to a solid dosage form such as a tablet, granule or other particle. The thickness of such a coating is usually between 20 and 100 µm.

› Film-coating formulations usually contain the following components:

Polymer.

Plasticizer.

Pigment/opacifier.

Vehicle.

Film Coating

› The properties and performance of the final coat is strongly affected by the polymerproperties and the formulation parameters. The coating formulation may contain othermajor components beside the polymer such as the solvent, plasticizers or pigments.Obviously, they can affect the performance of the coat by changing e.g. the mechanicalproperties, which will be discussed later.

› According to the interesting aspect for the specific use, the polymer may be classifiedas protective or functional coating. Based on their origin or preparation, natural, semi-synthetic or synthetic polymers are distinguished. Natural polymers are mostlysubjected to several purification steps, but without chemical modification. Usually,related to their origin, they are mixtures of different compounds, subjected to a certainvariability of their composition and thus the resulting performance.

› Semi-synthetic polymers are derived from a natural substance, receiving its specificproperty after certain chemical modifications. The cellulose derivatives used for coatingare one example of such materials. Synthetic polymers in contrast are fully chemicallysynthesized, as for example the methacrylic acid copolymers.

Type of film coating

Conventional film coating

• Apply to improve product appearance.

• Improve stability

• Ease of swallowing

Modified release film coating

• Effectively used either to sustain the release (extended release) or delay the release (enteric coating) of drug.

Sustained release film coating

• Act a membrane that allow infusion of fluid

• Application: Encapsulation & Tableting

Enteric film coating

• Drug delivery system to pass through the stomach intact and dissolve upon reaching the intestine.

CHAPTER 8: SOLID DOSAGE FORM COATING TECHNOLOGY8.5: QUALITY CONTROL REQUIREMENT

Quality

Definition:

The status of a drug that is determined by identity, purity, content, and other chemical,

physical, or biological properties, or by the manufacturing processes

Quality Control: Is a product oriented and focuses on defect identification.

Quality control of Tablets

General appearance

Size

ShapeThickness

Organoleptic Properties

Color

Odor

PHARMACOPOEIA

BRITISH INDIAN UNITED STATE

Uncoated tablet: Uncoated tablet: Physical tests applicable to tablet formulation:

Disintegration test Uniformity of container content Bulk density /Tapped density of powder

Uniformity of weight Content of active ingredient Powder fineness

Effervescent tablet: Uniformity of weight Loss on drying

Disintegration test Uniformity of content Disintegration test

Uniformity of weight Disintegration test Tablet friability

Coated tablet: Enteric coated tablet: Dissolution test

Disintegration test Disintegration test Drug release testing

Uniformity of weight Dispersible tablet: Uniformity of dosage form

Gastro resistant tablet: Uniformity of dispersion Container permeation test

Disintegration test Disintegration Labelling of inactive ingredients

Modified release tablet Soluble tablet:

Uniformity of weight. Disintegration test

Quality Control Requirement

› After coating the tablets should be inspected and tested. For appearance such as color, size and any physical defects. In vitro performance of the coated product is evaluated by disintegration and dissolution testing. Crushing strength of coated tablets can be determined with the tablet hardness tester. Stability studies must be conducted on the coated tablets to determine if temperature and humidity will cause film defects.

› Film Defects: Variation in formulation and or processing conditions may result in unacceptable quality defects in the film coating

› Sticking and picking: over wetting cause the tablet to stick to each other or to the coating pan which can be solved by reducing the rate of liquid application and or increase in drying air temperature.

› Roughness: A rough or the grity surface is a defect often observed when the coating solution is applied by spray. Some droplets may dry too rapidly before reaching the tablet as dried particle. To solve, move the nozzle closer to the tablet bed

Quality test for tablet

Friability

Weight Variation

Hardness

Friability Test

› Friability: It is the tendency of tablets to powder, chip, or fragment and this can affect the elegance appearance, consumer acceptance of the tablet, and also add to tablet’s weight variation or content uniformity problems

› Friability also is a property that is related to the hardness of the tablet.

› An instrument called friabilator is used to evaluate the ability of the tablet to withstand abrasion in packaging, handling, and shipping.

Friability Test

› For each formulation, the friability of 20 tablets was determined using Roche type friabilator. 20 tablets from each formulation were weighed and tested at a speed of 25 rpm for 4 min.

› After removing of dusts, tablets were re-weighed and friability percentage was calculated using the following equation.

› %Friability should 1% or less (The batch is Accepted)

› %Friability is more than 1% (The batch is Rejected)

Hardness Test

› Hardness (crushing strength): It is the load required to crush the tablet when placed on its edge.

Why do we measure hardness?

› To determine the need for pressure adjustments on the tableting machine.

› Hardness can affect the disintegration. So if the tablet is too hard, it may not disintegrate in the required period of time.

› If the tablet is too soft, it will not withstand the handling during subsequent.

Factor Affecting the Hardness:

Compression of the tablet.

Compressive force.

Amount of binder. (More binder, more hardness)

Method of granulation in preparing the tablet (wet method gives more hardness than direct method, Slugging method gives the best hardness)

Weight Variation Test

› Weight variation was carried out to ensure that, each of tablets contains the proper amount of drug.

› The test was carried out by weighing the 20 tablets individually using analytical balance, then calculating the average weight, and comparing the individual tablet weights to the average.

› The percentage of weight variation is calculated by using the following formula.

Standard Table for Weight Variation

Average weight of tablets

Deviation (%) Number of Tablets

Less than 80mg ± 10.0± 20.0

Minimum: 18Maximum: 2

80mg to 250mg ± 7.5± 15.0

Minimum: 18Maximum: 2

More than 250mg ± 5.0± 10.0

Minimum: 18Maximum: 2

SUMMARY

› Tablet coating is the process of evenly covering particles witha substance by applying a series of thin layers.

› Most coating processes use one of three general type ofequipment which are standard coating pan, the perforatedcoating pan and the fluidized bed (air suspension)

› A sugar coating is basically is a thick, hard coating of sugarsurrounding the tablet.

› After coating the tablets should be inspected and tested. Forappearance such as color, size and any physical defects.