Tablets – Industrial pharmacy – I B. Pharma 5th Semester PDF Notes

Tablets

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1 Tablets

Tablets - Industrial pharmacy - I

Introduction to Tablets

  • Solid medicaments may be administered orally as powders, pills, cachets, capsules or tablets
  • Solid unit dosage forms – contain a quantity of drug which is given as a single unit or dose
  • Tablets and capsules, currently account for well over two third of the total number and cost of medicines produced all over the world

Tablets – Introduction

  • Tablet is defined as a compressed solid dosage form containing medicaments with or without excipients
  • According to the Indian Pharmacopoeia Pharmaceutical tablets are solid, flat or biconvex discs, unit dosage form, prepared by compressing a drug or a mixture of drugs, with or without diluents

Tablets Ideal Properties

  1. A tablet should be elegant and free of defects like chips, cracks, discoloration, and contamination
  2. Should have sufficient strength to withstand mechanical shock during its production, packaging, shipping and dispensing
  3. Should have the chemical and physical stability to maintain its physical attributes over time
  4. The tablet must be able to release the medicinal agents in a predictable and reproducible manner

Tablets – Advantages

  1. They are unit dosage form and offer the greatest capabilities of all oral dosage form for the greatest dose precision and the least content variability
  2. Cost is lowest of all oral dosage form
  3. Lightest and compact compared all dosage forms
  4. Easiest and cheapest to package and ship
  5. Easy to swallowing with least tendency for ‘hang-up’ above the stomach
  6. Sustained release product is possible by coating techniques
  7. Must have a chemical stability over time so as not to allow alteration of the medicinal agents
  8. Objectionable odour and bitter taste can be masked by coating technique
  9. Suitable for large scale production
  10. Greatest chemical and microbial stability over all oral dosage form
  11. Product identification is easy and rapid requiring no additional steps when employing an embossed and/or monogrammed punch face

Tablets – Disadvantages

  1. Difficult to swallow in case of children and unconscious patients
  2. Some drugs resist compression into dense compacts, owing to amorphous nature, low density character
  3. Drugs with poor wetting, slow dissolution properties, optimum absorption high in GIT may be difficult to formulate or manufacture as a tablet that will still provide adequate or full drug bioavailability
  4. Bitter testing drugs, drugs with an objectionable odor or drugs that are sensitive to oxygen may require encapsulation or coating.

Tablet Formulation

  1. Diluent Formulation
  2. Binder or adhesive
  3. Disintegrant
  4. Lubricants and Glidents

Optional

  1. Coloring agents
  2. Flavoring agents
  3. Sweetening agents

Diluents / Fillers

 Diluents are fillers used to make required bulk of the tablet when the drug dosage itself is inadequate to produce the bulk

 Average tablet size: 3/16 inch to ½ inch

 Average weight range: 120 to 700mg (or 800mg for oval tablets)

 Secondary reason is to provide better tablet properties such as improve cohesion, to permit use of direct compression manufacturing or to promote flow.

A diluent should be

  1. Non toxic
  2. Commercially available in acceptable grade
  3. Low cost
  4. Physiologically inert
  5. Physically & chemically stable by themselves & in combination with the drugs
  6. Free from all microbial contamination
  7. Shoud not alter the bioavailability of drug
  8.  Color compatible

Commonly used tablet diluents

  1. Lactose-anhydrous and spray dried lactose
  2. Directly compressed starch (Sta-Rx 1500)
  3. Hydrolyzed starch (Emdex and Celutab)
  4. Microcrystalline cellulose (Avicel: Grades PH 101and PH 102)
  5. Dibasic calcium phosphate dihydrate
  6. Calcium sulphate dihydrate
  7. Mannitol
  8. Sorbitol
  9. Sucrose- Sugartab, DiPac, Nutab
  10. Dextrose

Binders and Adhesives

  • These materials are added either dry or in wet- form to form granules or to form cohesive compacts for directly compressed tablet

Commonly used Binders & Adhesive

  1. Starch paste paste -10-20 % solution
  2. Acacia, tragacanth – Solution for 10-25% Conc.
  3. Cellulose derivatives – Methyl cellulose, Hydroxy propyl methyl cellulose, Hydroxy propyl cellulose
  4. Gelatin- 10-20 % solution
  5. Glucose- 50 % solution
  6. Polyvinyl pyrrolidone (PVP)- 2% aqueous or alcoholic solutionàused as adhesive
  7. Sodium alginate
  8. Sorbitol

Disintegrants

  • Added to a tablet formulation to facilitate its breaking or disintegration when it contact in water in the GIT

Examples: Starch- 5-20% of tablet weight

Starch derivative – Primogel and Explotab (1-8%)

Clays- Veegum HV, bentonite 10% level in colored tablet only

Cellulose derivatives- Ac- Di-Sol (sodium carboxy methyl cellulose)

Alginate

Super- disintegrants

  • Swells up to ten fold within 30 seconds when contact water.
  • Examples: Crosscarmellose-cross-linked cellulose

Crosspovidone- cross-linked povidone (polymer)

Sodium starch glycolate- cross-linked starch

  • A portion of disintegrant is added before granulation and a portion before compression, which serve as glidants or lubricant
  • Evaluation of carbon dioxide in effervescent tablets is also one way of disintegration

Lubricant, Glidants and Antiadherants

 Lubricants are intended to reduce friction between the walls of the tablet and the walls of the die cavity and help in tablet ejection

 Glidants are intended to promote flow of granules or powder material by reducing the friction between the particles

 Antiadherents – reduce sticking or adhesion of any of the tablet granulation or powder to the faces of the punches or to the die wall

Lubricant,

Glidants

Antiadherants

• Stearic acid, Stearic acid salt – Stearic acid, Magnesium stearate, Talc, PEG (Polyethylene glycols), Surfactants

• Corn Starch – 5-10% conc., Talc-5% conc., Silica derivative – Colloidal silicas such as Cab-O-Sil, Syloid, Aerosil in 0.25- 3% conc

• Corn starch, talc, magnesium stearate, colloidal silica, SLS

Coloring Agents

  • Purpose?
  1. Masking of off color drugs
  2. Product Identification
  3. Production of more elegant product
  • All coloring agents must be approved and certified by FDA
  • Two forms of colors are used in tablet preparation – FD &C and D & C dyes

Dyes are applied as

Solutions in granulating agent

Lakes – Dyes that have been adsorbed on hydrous oxide à Used as dry powders

Precautions to be taken while using colours in tablet formulation

  • Water soluble dyes – use pastel shades
  • If tablets prepared by wet granulation – take care to prevent color migration during drying of the granules
  • The formulation should be checked for resistance to color changes on exposure to light

Commonly used Coloring agents 

   FD & C yellow 6-sunset yellow

   FD & C yellow 5- Tartrazine

   FD & C green 3- Fast Green

   FD & C blue 1- Brilliant Blue

   FD & C blue 2 – Indigo carmine

   FD & C red 3- Erythrosine.

   D & C red 22 – Eosin Y

Flavours

  • Limited for chewable tablets and tablets intended to dissolve in the mouth
  • Flavour oils – 0.5 to 0.75%
  • Flavour oils can be used as solvents added to tablet granulation, dispersed on clays or other adsorbents or emulsified in aqueous granulating agents

Sweetening agents

For chewable tablets: Sucrose, mannitol (72% as sweet as sucrose)

   Saccharin (artificial): 500 time’s sweeter than sucrose

Disadvantage: Bitter aftertaste and carcinogenic

   Aspartame (artificial)

Disadvantage: Lack of stability in presence of moisture

Tablets Classification

Tablets ingested orally

  • Compressed tablet or standard compressed tablet (CT)
  • Multiple compressed tablet (MCT)
  • Layered tablets
  • Compression-coated tablets
  • Repeat action tablets
  • Delayed action and enteric coated
  • Sugar coated tablet
  • Film coated tablet
  • Chewable tablet

Tablets used in oral cavity

  • Buccal tablet
  • Sublingual tablet
  • Troches or lozenges
  • Dental cone

Tablets administered by other route

  • Implantation tablet
  • Vaginal tablet

Tablets used to prepare solution

  • Effervescent tablet e.g. Dispirin tablet (Aspirin)
  • Dispensing
  • Hypodermic tablet
  • Tablet triturates e.g. Enzyme tablet (Digiplex)

Compressed tablets (C.T.)

  • These tablets are uncoated and made by compression of granules
  • Meant to be swallowed, get disintegrated in the stomach and its drug contents are absorbed in the gastrointestinal tract and distribute in the whole body

Multi compressed tablets (M.C.T.)

  • These tablets are prepared

– To separate physically or chemically incompatible ingredients

– produce repeat-action or prolonged-action products

  • A special type of tablet making machine is used which provides two compressions

Multilayered tablets

  • These tablets consist of two or more layers of materials compressed successively in the same tablets
  • The colour of each layer may be the same or different
  • To separate incompatible ingredients physically

Sustained action tablets

  • To get a sustained action of medicament
  • To maintain the maximum effective concentration of the drug in the blood throughout the period of treatment

Enteric coated tablets

  • Designed to bypass the stomach and get disintegrated in the intestines only

Sugar coated tablets

  • Compressed tablets having a sugar coating are called “sugar coated tablets”
  • Sugar coating is done to mark the bitter and unpleasant odour and the taste of the medicament
  • Elegant in apprearance
  • Protection

Film coated tablets

  • The compressed tablets having a film coating of some polymer substance, such as hydroxypropyl cellulose, hydroxypropylmethyl cellulose and ethyl cellulose.
  • The film coating protects the medicament from atmospheric effects
  • Film coated tablets are generally tasteless, having little increase in the tablet weight and have less elegance than that of sugar coated tablets

Chewable tablets

  • Chewed in the mouth and broken into smaller pieces
  • The disintegration time is reduced and the rate of absorption of the medicament is increased

Buccal tablets

  • To be placed in the buccal pouch or between the gums and lips or cheek
  • They dissolve or disintegrate slowly and are absorbed directly without passing into the alimentary canal

Sublingual tablets

  • To be placed under the tongue where they dissolve or disintegrate quickly and are absorbed directly without passing into GIT

Lozenge tablets and troches

  • Designed to exert a local effect in the mouth or throat
  • These tablets are commonly used to treat sore throat or to
  • control coughing in common cold
  • They may contain local anaesthetics, antiseptic, antibacterial agents, astringents and antitussives
  • These are prepared by compression at a high pressure or by the moulding process and generally contain a sweetening agent, a flavouring agent and a substance which produces a cooling effect along with medicaments

Dental cones

  • Small compressed tablets meant for placing them in the empty sockets after tooth extraction
  • They prevent the multiplication of bacteria in the socket following such extraction by using slow releasing antibacterial compounds or to reduce bleeding by containing the astringent
  • Cones generally get dissolved in 20 to 40 minutes time

Implantation tablets

  • Placed under the skin or inserted subcutaneously by means of minor surgical operation and are slowly absorbed
  • Must be sterile and should be packed individually
  • Mainly used for administration of hormones such as testosterone and deoxycorticosterone etc.

Vaginal tablets

  • Meant to dissolve slowly in the vaginal cavity
  • Steroids, antibacterial agents, antiseptics or astringents to treat vaginal infections
  • The tablets are often buffered to promote a pH favourable to the action of a specified antiseptic agent

Effervescent tablets

  • When added in water produce effervescence
  • Dssolved rapidly in water due to the chemical reaction which takes place between alkali bicarbonate and citric acid or tartaric acid or combination of both
  • These tablets are to be protected from atmospheric moisture during storage

Dispensing tablets

  • Contain excipients which gets dissolved quickly to form a clear solution
  • Antiseptic tablets
  • Nor for consumption
  • Mild silver proteinate, bichloride of mercury merbromin and quarternary ammonium compounds

Hypodermic tablets

  • Compressed tablets which are composed of one or more drugs with readily water soluble Ingredients dissolved in sterile water or water for injection and administered by parenteral route

Tablet triturates

  • Small tablets usually cylindrical, moulded or compressed, and contain a potent medicament with a diluent
  • On a small scale, tablet triturates are prepared by using hand- operated tablet triturates moulds but for bulk production, automatic tablet triturate machines are used

Essential properties of Powders intended for compression into tablets

 Powder fluidity or flowability

  • The material can be transported through the hopper into the die
  • To produce tablets of a consistent weight
  • Powder flow can be improved mechanically by the use of vibrators or incorporation of the glidant

 Powder compressibility

  • The property of forming a stable, intact compact mass when pressure is applied is called powder compressibility

 Easily mixed with other particles

 Homogenous colouring etc.,

 Friction and adhesion properties

Manufacture of Tablets

1. Dry method:

Direct Compression

Slugging or Double compression

2. Wet method

DIRECT COMPRESSION

  • Few steps – do not require much equipments and handling expenses
  • The medicaments with large doses having good bulk density, flowability and compressibility can be directly compressed
  • The different stages involved are:
  1. Milling / size reduction
  2. Blending
  3. Compression.

Advantages and Disadvantages of Direct Compression

Advantages

  • Less amount of additives are used in the formulation
  • Number of steps involved are minimum
  • Less equipments are used
  • Less time consuming

Disadvantages

  • All medicaments cannot be compressed directly

Requirements for direct compression

  • Dose of medicament/ drug should be more
  • The medicaments should have very good mechanical strength and cohesiveness
  • Medicament should have very good compressibility and other derived properties such as bulk density, angle of repose etc

Slugging or Double compression Method

  • Used for those drugs which are sensitive to heat, moisture or both
  • Also called compression granulation

STEPS IN COMPRESSION GRANULATION

Step 1: Slugging

Compaction of tablet components using a special tablet press

Dies of large capacity compacted by means of flat punches

Compacted masses is called “Slugs”

The process is refeed to as “slugging”

Step 2: MillingStep 3: Screening

If single slugging process in insufficient, to confer the desired granular properties, the slugs can be screened and slugged again

Compression Granulation

Granulation

  • Defined as a size enlargement process which converts fine or coarse particles into physically stronger and larger agglomerates having good flow property, better compression characteristics and uniformity
  • The art and science for process and production of granules is known as Granulation Technology

Need for Granulation

To avoid powder segregation

Segregation results in weight variation

To enhance the flow properties of powder

Higher flowability gives better filling of the dies and containers

To produce uniform mixtures

Mixtures of various particles tend to segregate during transport and handling due to differences in particle, size and density

To produce dust free formulations

Reduce dust generation and avoid employee exposure to drug product

To eliminate poor content uniformity

To improve compaction characteristics

Makes hydrophobic surfaces more hydrophilic

Better distribution of color and soluble drug if added in the binding solution

Disadvantages

 Process is expensive because of labor, space, time, special equipment and energy requirement

 Loss of material during various stages of processing

 Moisture sensitive and thermolabile drugs are poor candidates

 Any incompatibility between the formulation components is aggravated during the processing

Wet granulation

Involves

 Wet massing of powders

 Wet sizing/ milling

 Drying

Procedure of Wet Granulation

Step 1:  Weighing and Blending

Step 2:  Wet granulate prepared by adding the binder solution

Step 3: Screening the damp mass into pellets or granules (6-8mesh)

Step 4: Drying the granulation in thermostatically controlled ovens

Step 5: Dry screening

Step 6: Mixing with other ingredients: A dry lubricant, antiadherent and glidant, colorant, disintegrant

Step 7: Tableting: Last step in which the tablet is fed into the die cavity and then compressed.

  • Forms granules by binding the powders together with an adhesive

Depending on the solubility of binder and other mixture components

  1. Employs a solution, suspension or slurry containing a binder the binder is added to powder mixàMethod used when large quantity of binder is required
  2. Binder is added as dry powder to the power mix liquid is added lateràMethod is used when only a small quantity of binder is permissible

Mechanism of Granulation

  • Liquid bridges are formed between the particles
  • Tensile strength of these bonds increases as the amount of liquid increases
  • Time required – depends on the wetting property of the powders, granulating fluid and efficiency of the mixer
  • Rough way of detrmining is to press the mixture in the palm of the hand… if the mass crumbles with slight pressure, it is ready for nxt stage in processing

Wet Screening

  • Conversion of the moist mass into coarse, granular aggregates or passing through a hammer mill or oscillatory granulator having screens with larger perforations

Purpose?

  • Consolidate granules
  • Increase particle contact point
  • Increase surface area to facilitate drying

Drying of Granules

  • To remove the solvent used to form aggregates
  • To obtain optimum moisture level in granule
  • Drying results in the formation of interparticulate bonds like Vand der Walls forces

Screening of dried granules

  • Depending on the granulating equipment used and the size of tablet to be made, the dried granules are screened to obtain a more uniform distribution of the granules

Wet granulation methods

Single pot granulation

High shear mixture granulation

Fluid bed granulation

Extrusion- Spheronization

Single pot granulation

The granulation is done in a normal high shear processor and dried in same equipment e.g. Single Pot Processor / One- Pot Processor

High shear mixture granulation

Step 1: Dry Powder mixing (Approx 2-5 mins)

Step 2: Liquid binder addition (Approx 1-2 mins)

Step 3: Wet massing

Step 4: Wet sieving of granules

Step 5: Drying

Step 6: Dry sieving of granules

 It involves typically 3 phases:

  1. Dry Powder mixing (2-5 mins)
  2. Liquid binder addition (1-2 mins)
  3. Wet massing

Advantages:

Highly cohesive material can be granulated

Disadvantages:

Mechanical degradation

ADVANTAGES                                                  

  • Short processing time
  • Lesser amount of liquid binders required
  • Highly cohesive material can be granulated

 DISADVANTAGES

  • Increase in temperature may cause chemical degradation of thermolabile material
  • Over wetting of granules can lead to large size lumps formation

Fluid bed Granulation

  • Fluid bed granulation is a process by which granules are produced in singl equipment by spraying a binder solution onto a fluidized powder bed.
  • The material processed by fluid bed granulation are finer free flowing and homogeneous

Advantages

  1. It reduces dust formation during proces.
  2. It reduces product loss
  3. It improves worker safety

Disadvantages

  1. The Fluid Bed cleaning is labor-intensive and time consuming
  2. Difficulty of assuring reproducibility

n  Homogeneous granules.

n  Gentle product handling.

n  Uniform spraying of all particles in the fluid bed.

Extrusion-Spheronization

This process is primarily used as a method to produce multi- particulates for controlled release application

It is a multiple step process involving at least 5 steps capable of making uniform sized spherical particles

  1. Dry mixing of materials to achieve homogeneous dispersion
  2. Wet granulation of the resulted mixture to form wet mass
  3. Extrusion of wet mass to form rod shaped particles
  4. Rounding off (in spheronizer)
  5. Drying – These dried rounded particles can be optionally screened to achieve a targeted mean size distribution

Advantages                         

  1. Two or more active agents can be easily combined in any ratio in the ame unit
  2. Physical characteristics of the active ingredients and excipients can be modified
  3. Particles having high bulk density, low hygroscopicity, high spherocity, and dust free, narrow particle size distribution and smoother surface can be produced

Disadvantages

  1. This process is more labor and time Intensive than other commonly used granulation techniques

Limitations of wet granulation

Advanced Granulation Techniques

 Steam Granulation

 Melt Granulation

 Moisture Activated Dry Granulation (MADG)

 Moist Granulation Technique (MGT)

 Thermal Adhesion Granulation Process (TAGP)

 Foam Granulation

 Pneumatic Dry Granulation (PDG)

 Freeze granulation Technology

 Steam Granulation

 Melt Extrusion Technology

 Liquisolid Technique

 TOPO Technology

 Continuous Flow Technology

Processing Problems in Tablets

Capping and lamination

Picking and sticking

Mottling

Weight variation

Hardness variation

Double impression

Capping and Lamination

  • Capping is the term used to describe the partial or complete separation of the top or bottom crowns of a tablet
  • Lamination is separation of a tablet into two or more distinct layers

Detection

  • Friability test is the quickest way to determine such problems

Reasons

  • During compression, air is entrapped among the particles or granules and does not escape until the compression pressure is released
  • Issues related to tablet tooling

Solution/ Remedies

  • Precompression
  • Slowing the tableting rate
  • Reducing the final compression pressure
  • Replacing deep concave punches with flat punches
  • Retaining certain amount of moisture in the granulation
  • The concave or bevelled edges of the punches gradually curve inward with use and form a “claw”
  • This pull the crowns off the tablet
  • Dies develop a wear ‘ring’ in the area of compression. Can be prevented by using tungsten carbide inserts in thee dies
  • Tablets can cap during ejection
  • Incorrect setting up of the press

Picking and sticking

  • Small amount of material from a tablet is sticking to and being removed off from the tablet-surface by a punch face
  • Sticking refers to tablet material adhering to the die wall
  • The problem is more prevalent on the upper punch faces than on the lower ones

Reasons

  • Punch tips have engraving or embossing letters

– Can be prevented by designing the lettering as larger as possible

– Tablets may be reformulated into a larger size

– Plating of punch faces with chromium

  • Granular material is improperly dried

CAUSES

REMEDIES

Excessive moisture in granules

Dry properly the granules, determine optimum limit

Too little or improper lubrication

Increase lubrication; use colloidal silica as a ‘polishing agent’, so that material does not cling to punch faces

Low melting point substances, may soften from the heat of compression and lead to picking

Add high melting-point materials. Use high meting point lubricants

Low melting point medicament in high concentration

Refrigerate granules and the entire tablet press

Too warm granules when compressing

Compress at room temperature. Cool sufficiently before compression

Too much amount of binder

Reduce the amount of binder, change the type or use dry binders

Mottling

  • Unequal distribution of color on a tablet, with light or dark spots

Reason

  • Colored drug, whose color differs from the color of excipients used for granulation of a tablet

CAUSES

REMEDIES

A coloured drug used along with colourless or white-coloured excipients

Use appropriate colourants

A dye migrates to the surface of granulation while drying

Change the solvent system, Change the binder, Reduce drying temperature and Use a smaller particle size

Improperly mixed dye, especially during ‘Direct Compression’

Mix properly and reduce size if it is of a larger size to prevent segregation

Improper mixing of a coloured binder solution

Incorporate dry colour additive during powder blending step, then add fine powdered adhesives such as acacia and tragacanth and mix well and finally add granulating liquid

Weight Variation

  • Anything that can alter the die fill process can cause weight variation in tablets
  1. Granule size and size distribution before compression
  2. Poor flow
  3. Poor mixing
  4. Punch variation

Hardness Variation

  • Hardness depends upon the tablet weight
  • All the reasons affecting weight variation also will affect the hardness

Double Impression

  • Involves only those punches, which have a monogram or other engraving on them
  • If the upper punch is uncontrolled, it can rotate during the short travel to the final compression stage and create a double impression

Reason:

  • At the moment of compression, the tablet receives the imprint of the punch
  • The lower punch freely drops and travels uncontrolled for a short distance before riding up the ejection cam to push the tablet out of the die
  • Nowduring  this  free  travel,  the  punch  rotates and  at  this point, the punch may make a new impression on the bottom of the tablet, resulting in ‘double impression’

Remedy

  • Using keying tools that prevent punch rotation
  • Newer punches have anti-turning rotation

Tablet Coating

Introduction

  • Coating is a process by which an essentially dry, outer layer of coating material is applied to the surface of a dosage form

In order to confer specific benefits

 facilitating product identification

 To modifying drug release from the dosage form

Coating Objectives

  • To mask the taste, odor or color of the drug
  • To provide physical and chemical protection
  • To control the release of the drug
  • To protect the drug from GI environment of the stomach
  • To incorporate another ingredient in the coating – avoid incompatibility or for sequential release
  • To improve elegance

Components involved in tablet coating

1. Tablet properties

2. Coating process

Coating equipment

Parameters of the coating process

Facility and ancillary equipment

Automation in coating processes

3. Coating composition

Tablet properties

Tablet must be resistant to abrasion and chips

The ideal shape of the tablet for coating is sphere

Tablet surface should be wettable by the coating solution

Coating process – equipment

  • Standard coating pan
  • Perforated coating pan
  • Fluidised bed (air suspension coater)

Standard coating pan

  • Circular metal pan
  • Mounted angularly on a stand
  • 8 to 60 inches in diameter
  • Rotated on horizontal axis using motor
  • Heated air is directed into the pan and exhausted by means of duct
  • Coating solution applied to the tablet by ladling or spraying

Modifications

  • Pellegrini pan –baffled pan with a diffuser
  • Immersion sword system –drying air is introduced through a perforated metal sword device immersed in the tablet bed. Coating solution applied through a automated spray system
  • Immersions tube system –tube immersed in the tablet bed delivers heated air and coating solution

Perforated coating pan

  • Consists of a perforated or partially perforated drum that rotates on its horizontal axis in an enclosed housing
  • Accela cota & Hi coater system –drying air is directed into the drum  passes through the tablet bed  exhausted through perforations in the drum
  • Driacoater –introduces drying air through hollow coated ribs located on the inside periphery of the drum. Air exhaust is from the back of the pan
  • Glatt coater –drying air directed from inside the drum, through the tablet bed and out an exhaust duct
  • Coating solution applied as a spray onto the tablet bed

Fluidized bed (Air suspension) system

Fluidization of the tablet bed in a column of heated air

Coating solution applied with the help of a spray nozzle at the bottom

Air suspension coating

Spray application systems

High pressure airless

 Coating liquid pumped at high pressure through a small orifice 250 to 3000 psig

Low pressure air atomised

 Liquid pumped through larger orifice at 5 to 50 psig

 Low pressure air (10 to 100psig) contacts the liquid stream at the tip of the automizer to produce a spray

Coating composition

  • Most of the coating composition is solvent
  • Rapid removal (drying) is necessary
  • Use of high temperatures must be carefully monitored (stability)
  • Viscous, aqueous based coating solutions – require longer drying periods
  • Thin, rapidly drying formulations dry quickly allowing constant application

Types of tablet coating

  1. Sugar coating
  2. Film coating

Sugar coating

  • Involves several stages
  • Few hours to a few days
  • Ideal tablet shape – deep convex surfaces with thin rounded edges
  • Final tablet appearance is elegant and glossy

Steps in sugar coating

Step 1: Sealing

Step 2: Subcoating

Step 3: Syruping (smoothing)

Step 4: Finishing

Step 5: Polishing

Seal coating

Why?

  • To prevent moisture penetration into the tablet core

Polymer used

  • Shellac
  • Zein (protein derivative from corn)

Subcoating solution

  • Gelatin, acacia, cane sugar, corn syrup, etc.

Subcoating powders

  • Kaolin, dextrin, cocoa, calcium carbonate, etc

Subcoating 

Why?

  • To round the edges and build up the tablet size

How?

  • Alternately applying sticky binder solution followed by dusting of subcoating powder and drying

Subcoating solution

  • Gelatin, acacia, cane sugar, corn syrup, etc.

Subcoating powder

  • Kaolin, dextrin, cal. carbonate, Acacia powder, etc.

Effect on tablet

  • Increases tablet weight by 50 to 100%

Syrup (smoothening/colour) coating

Why?

  • To cover and fill in the imperfections on the tablet surface & to impart desired colour

Steps

  • Grossing syrup, Heavy syrup, Regular syrup

Grossing syrup

  • Contains suspended powders and a light colouring

Heavy syrup

  • Syrup solutions containing dye

Regular syrup

  • Clear coats of only syrup

Polishing

Why?

  • To obtain the desired luster

How?

  • Tablets polished in clean standard coating pan lined with canvas

Polishing solution

  • Powders waxes or warm solutions of waxes (beeswax or carnauba wax) in suitable volatile solvents

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