Tablet - Classification, Method of Preparation and Evaluation

Tablet’s
Ms. Chitralekha G. Therkar
Assistant Professor
Department of Pharmaceutics,
Siddhivinayak College of Pharmacy, Warora

Introduction
 The solid dosage forms were commonly used in conventional days for its various
advantages.
 According to the Indian Pharmacopoeia, Pharmaceutical Tablets are defined as solid, flat
or biconvex disks of unit dosage form which are prepared by compressing a drug or a
mixture of drugs, with or without excipients.
 According to USP, Tablet is defined as a compressed solid, unit dosage form containing
medicaments with or without excipients.
 Tablets are solid dosage form in which one usual dose of the drug has been accurately
placed and that’s why they are the most popular form of medication.
 They come in different sizes and shapes.
 Size varies from a few mm to a cm and it depends upon the quantity of medicament.

Ideal Characteristics of Tablets
 It must be an elegant product with an appropriate size and shape since the size and
shape influences tablets passing through pharynx and esophagus.
 It should be free from all the defects like chipping, capping, mottling, orange peel
effect and lamination etc.
 The tablet must be sufficiently strong and should have proper mechanical strength
so it can withstand during manufacturing, shipping and use.
 The tablet must be uniform in weight and in drug content.
 The tablet should be able to release its content in a predictable and reproducible
manner and get absorbed in systemic circulation.
 The tablet should be chemically stable so that there should be no alteration of the
medicinal agent with time.

1. From patients point of view
 They are easy to carry, easy to swallow and are attractive in appearance.
 Unpleasant taste can be masked by sugar coating and do not require any extra
measurement of dose.
 Some tablets are divided into halves and quarters by drawing lines during
manufacturing for easy breakage if any fractional dose is required in case of children.
Advantages of Tablet Dosage Form

2. From manufacturer’s point of view
 An accurate amount of medicament, even if very small, can be incorporated.
 Tablets provide best combined properties of chemical, mechanical and
microbiological stability of all the oral dosage forms.
 Since they are generally produced on a large scale, therefore, their cost of
production is relatively low, hence economical.
 They are in general the easiest and cheapest to package and ship among all oral
dosage forms.
 Some specialized tablets may be prepared for modified release profile of the drug.
 Product identification is potentially the simplest and cheapest requiring no
additional processing steps when employing an embossed or monogrammed
punch face.

 Difficult to swallow in case of children and unconscious patients.
 Drugs with poor wetting, slow dissolution, high absorption in GIT may be difficult to
formulate as a tablet.
 Bitter testing drugs, drugs with bad odour or drugs that are sensitive to oxygen may
require encapsulation or coating. In such cases, capsule may offer the best and lowest cost.
 Some drugs resist compression into dense compacts, owing to amorphous nature or low
density characteristics of drugs.
 Hygroscopic substance can’t be used because it may adhere to the die walls.
 First pass metabolism occurs and have less bioavailability compared to parenteral route.
 Amorphous compounds and low density compounds are difficult to compress.
Disadvantages of Tablet Dosage Form

Tablets ingested orally –
1. Compressed tablets
2. Multiple compressed tablets
3. Enteric coated tablets
4. Sugar coated tablets
5. Film coated tablets
6. Chewable tablets
Tablets administered by other routes –
1. Implantation tablets
2. Vaginal tablets
Types of tablets
Tablets used in the oral cavities –
1. Buccal Tablets
2. Sublingual tablets
3. Lozenges
4. Dental cones
Tablets used to prepare solutions –
1. Effervescent tablets
2. Dispensing tablets
3. Hypodermic tablets
4. Tablet triturates

1. Compressed Tablets
 These tablets are formed by compression and contain no special coating.
 They are made from powdered, crystalline or granular material, alone or in
combination with excipients.
 These tablets contain water soluble drugs which after swallowing get disintegrated
in the stomach and its drug contents are absorbed in the gastrointestinal tract and
distributed in the whole body.
 Eg. Aspirin (Disprin), Paracetamol Tablets (Crocin)
1. Tablets Ingested Orally

2. Multiple Compressed Tablets / Layered Tablets
 These are compressed tablets made by more than one compression cycle.
 Such tablets are prepared by compressing additional tablet granules on a
previously compressed granules.
 The operation may be repeated to produce multilayered tablets of two or three
layers.
 To avoid incompatibility, the ingredients to be used in the formulation except the
incompatible material are compressed into a tablet and then incompatible
substance along with excipients are compressed over the previously compressed
tablet.

3. Sustained Action Tablets
 These are the tablets which after oral administration release
the drug at a desired time and prolong the effect of the
medicament.
 These tablets when taken orally release the medicament in a
sufficient quantity as and when required to maintain the
maximum effective concentration of the drug in the blood
throughout the period of treatment.
 Eg. Diclofenac SR tablets.
4. Enteric Coated Tablets
 These are compressed tablet meant for administration by
swallowing and are designed to bypass the stomach.
 This tablets get disintegrated in intestine only.
 These tablets are coated with materials resistant to acidic pH
like cellulose acetate phthalate of the gastric fluid but get
disintegrated in the alkaline pH of the intestine.

5. Film Coated Tablets
 The compressed tablets having a film coating of some
polymer substance, such as hydroxy propyl cellulose,
hydroxy propyl methyl cellulose and ethyl cellulose.
 These film coating protects the medicament from the
atmospheric effects and moisture.
 Film coated tablets are generally tasteless, having little
increase in the tablet weight and have less elegance than
that of sugar coated tablets.
6. Chewable Tablets
 These are the tablets which are required to be broken and
chewed in between the teeth before ingestion.
 These tablets are given to the children who have difficulty
in swallowing and to the adults who dislike swallowing.
 These tablets should have very acceptable taste and flavour.
 Eg. Antacid tablets (Digiene), Gelusil

7. Sugar coated tablets
 These are compressed tablets containing a sugar coating.
 Such coatings are done to mask the bitter taste and unpleasant odour of the
medicament.
 The sugar coating makes the tablet elegant and it also safeguard the drug from
atmospheric effects.

1. Buccal Tablets
 These tablets are to be placed in the side of the cheek (buccal
pouch) where they dissolve or erode slowly and are absorbed
directly in the buccal cavity without passing into the
alimentary canal.
 Therefore, they are formulated and compressed with
sufficient pressure to give a hard tablets.
 Eg. Progesterone tablets.
2. Sublingual Tablets
 These tablets are to be placed under the tongue where they
dissolve or disintegrate quickly and are absorbed directly
without passing into GIT.
 Eg. Tablets of nitroglycerin, Isoproterenol hydrochloride
2. Tablets used in oral cavity

3. Lozenges Tablets
 These tablets are designed to exert a local effect in the mouth or throat.
 These tablets are commonly used to treat sore throat to control coughing in
common cold.
 They may contain local anaesthetics, antiseptics, antibacterial agents and
astringents.
 These are prepared by compression at a high pressure by the moulding
process and generally contain a sweetening agent, flavouring agent and a
substance which reduces a cooling effect.
 Eg. Vicks lozenges, Strepsils.

4. Dental Cones
 These are compressed tablets meant for placement 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.
 These tablets contains an excipients like lactose, sodium bicarbonate and sodium
chloride.
 These cones generally get dissolved in 20 to 40 minutes time.

1. Vaginal Tablets
 These tablets are meant to dissolve slowly in the vaginal cavity.
 The tablets are typically oval or pear shaped for the ease of insertion, these tablets
are used to release steroids or antimicrobial agents.
 The tablets are often buffered to promote a pH favorable to the action of a specified
antimicrobial agent.
 They contain easily soluble components, lactose or sodium bicarbonate.
3. Tablets administered by other routes

2. Implantation Tablets
 These tablets are placed under the skin or inserted subcutaneously by means of minor
surgical operation and are slowly absorbed.
 These may be made by heavy compression but are normally made by fusion.
 The implants must be sterile and should be packed individually.
 Implants are mainly used for the administration of hormones such as testosterone,
steroids for contraception.
 These tablets are very usefully exploited for birth control purpose in human beings.
 The disadvantages of implant tablets are their administration, changing rate of release
with change of surface area and possibility of tissue reactions.

4. Tablets used to Prepare Solutions
1. Effervescent Tablets
 These tablets along with the active medicament contain ingredients like sodium
bicarbonate, citric acid and tartaric acid which react in the presence of water.
 It liberate carbon dioxide and producing effervescence leading to disintegration of
the tablet, thus fastens solution formation and increase the palatability.
 Eg. Histac (Ranitidine), Disprin

2. Dispensing Tablets
 These tablets provide a convenient quantity of potent drug that can be readily
convert into powders and incorporate into liquids, thus can be used to weigh small
quantities.
 These tablets are primarily given as convenience for extemporaneous compounding
and should never be dispensed as dosage form.
 The drugs commonly incorporated are mild silver potentiate, quarternary
ammonium compounds.

3. Hypodermic Tablets
 Hypodermic tablets are soft, readily soluble tablets and
originally were used for the preparation of solutions to be
injected.
 These tablets are dissolved in sterile water or water for
injection and administered by parenteral route.
 These tablets are not preferred now-a-days because the
resulting solution is not always sterile
4. Tablet triturates (Moulded tablets)
 These are powders moulded into tablets.
 They are flat, circular discs, usually containing a potent
substance mixed with lactose, lactose and sucrose,
dextrose, or other suitable diluent.
 Since they are intended to disintegrate very quickly in
contact with moisture, water insoluble adjuncts are
avoided.
 The name ‘tablet triturate’ is appropriate because they
usually contain trituration's (trituration - Dilution with an
inert substance).

 In addition to active ingredients, tablet contains a number of inert materials known as
additives or excipients.
 Different excipients are as follows,
1. Diluent / Fillers
2. Binder and adhesive
3. Disintegrants
4. Lubricants
5. Glidants
6. Colouring agents
7. Flavoring agents
8. Sweeteners
Tablet Ingredients/ Excipients

 Impart weight, accuracy and volume to the tablets.
 Improve solubility of whole dosage form
 Increase mechanical stability of tablets.
 Enhance bioavailability and permeability.
 Modifying drug release of dosage form (Superdisintegrants).
 Increase patient acceptability and compliance’s.
 Facilitate dosage form design (Various convenient shapes and sizes).
Functions of Excipients

Definition –
Diluents are the fillers used to make the required quantity of tablet when the drug dose
itself is inadequate to produce the whole bulk. Also a secondary reason is to provide better
tablet properties such as to improve mechanical strength, to permit the use of direct
compression manufacturing or to promote flow.
A diluent should have following properties,
1. They must be non-toxic and low cost.
2. They must be commercially available in acceptable grade.
3. They must be physiologically inert, physically and chemically stable by themselves and
in combination with the drugs.
4. They must be free from all microbial contamination.
5. They do not alter the bioavailability of drug.
6. They must be color compatible.
1. Diluents

Ideal characteristics of diluents –
1. They must be nontoxic and acceptable to the regulatory agencies in all countries where
the product is to be marketed.
2. They must be commercially available in an acceptable grade in all countries where the
product is to be manufactured.
3. They must be cheap compared to the active ingredients and must be physiologically inert.
4. They must be chemically stable alone or in combination with the drugs or other tablet
components.
5. They must be color compatible should not produce any off color appearance over tablet.
6. They must have no negative effects on the bioavailability of the drugs in the product.
Commonly used tablet diluents are as follows,
1. Lactose anhydrous and Spray dried Lactose
2. Directly compressed starch (Sta Rx 1500)
3. Celutab
4. Microcrystalline Cellulose (MCC)
5. Dibasic calcium phosphate
6. Mannitol and Sorbitol
7. Dextrose

Definition –
Agents used to impart cohesive qualities to the powdered material are referred to as binders
or granulators.
Objective of incorporating binders
1. They impart a cohesiveness to the tablet formulation (both direct compression and wet
granulation method) which insures the tablet remaining intact after compression.
2. They improves the free flowing qualities by the formation of granules of desired size and
hardness.
MOP –
Corn starch is dispersed in cold purified water to make a 5 to 10% w/w suspension and then
warming in water bath with continuous stirring until a translucent paste is formed.
 Liquid glucose - 50% solution in water is fairly common binding agent.
 Sucrose solution - 50% to 74% sugar solution is used as binder.
 They produce hard but brittle granules.
2. Binders and Adhesive

Definition –
 A disintegrant is a substance added to a mixture of substances or added to tablet to
facilitate its breaking or disintegration after administration in the GIT.
 The active ingredients must be released from the tablet matrix as efficiently as possible
to allow for its rapid dissolution.
 Disintegrants can be classified chemically as; starches, clays, celluloses, alginates,
gums and crosslinked polymers.
 Eg, Starch (Corn starch, Potato starch)
 For their disintegrating effect starches are added to the powder blends in dry state.
Superdisintegrants – Ingredients which get disintegrate very fast.
1. Super disintegrants like Croscarmelose - Cross linked cellulose
2. Crospovidone - Cross linked polyvinyl pyrrolidone
3. Sodium starch glycolate - Cross linked starch
3. Disintegrants

Definition –
Lubricants are intended to prevent adhesion of the tablet materials to the surface of dies
and punches, reduce inter particle friction and may improve the rate of flow of the tablet
granulation.
Objectives –
1. Prevents adhesion of the tablet material to the surface of dies and punches.
2. Reduce inter-particular friction, improve the rate of flow of tablet granulation.
3. Facilitate ejection of the tablets from the die cavity.
Egs –
 Stearic acid
 Magnesium stearate
 Talc
 PEG (Polyethylene glycols)
 Surfactants.
4. Lubricants

Definition –
Glidants are intended to promote flow of granules or powder material by reducing the
friction between the particles.
Egs –
Corn Starch – 5-10%
Talc-5%
Silica derivative - Colloidal silicas such as Cab-O- Sil
Syloid
Aerosil in 0.25-3%
Antiadherents are used for the purpose of reducing the sticking or adhesion of any of the
tablet ingredients or powder to the faces of the punches or to the die wall.
5. Glidants

Definition –
This are the substances which are used in the dosage form to impart colour to them for
better appearance or for colour masking.
Objectives –
1. It makes the tablet more esthetic in appearance.
2. Colour helps the manufacturer to identify the product during its preparation.
3. Colorants are obtained in two forms dyes and lakes.
4. Dyes are dissolved in the binding solution prior to the granulating process.
5. However, during drying their color may migrate to the surface and may produce
mottling of the tablet.
6. So another approach is to adsorb the dye on starch or calcium sulfate from its aqueous
solution; the resultant powder is dried and blended with other ingredients.
7. Color lakes are dyes which are adsorbed onto a hydrous oxide of a heavy metal (like
Aluminium) resulting in an insoluble form of the dye.
6. Coloring agent

Definition –
Flavours are usually limited to chewable tablets or other tablets intended to dissolve in the
mouth. Flavor oils are added to tablet granulations in solvents, are dispersed on clays and
other adsorbents or are emulsified in aqueous granulating agents (i.e. binder).
The use of sweeteners is primarily limited to chewable tablets.
Egs,
1. Sugar
2. Mannitol– 72% as sweet as sugar, cooling & mouth filling effect
3. Saccharin– Artificial sweetener, 500 times sweeter than sucrose
4. Cyclamate– either alone or with saccharin
5. Aspartame – widely replacing saccharin
Disadvantages –
1. It has a bitter after taste
2. Carcinogenic
3. Lack of stability in presence of moisture
6. Flavours and Sweeteners

Manufacture of tablets involves certain well defined steps namely namely as follows,
1. Pulverization and mixing
2. Granulation
3. Compression
4. Coating (if required)
5. Tablet Evaluation
6. Tablet Defects
1. Pulverization and Mixing –
 In this step the different solid / powder ingredients are reduced to the same particle
size since particles of different sizes will segregate while mixing.
 Various equipment's like Cutter mill, Hammer mill, Roller mill and Fluid energy mill is
required to reduce the large lumps.
Manufacturing of Tablets

2. Granulation – It is the process in which primary powder particles are made to adhere
to form large multi-particle entities.
Range of size - 0.2 mm to 4 mm (0.2 mm to 0.5 mm)
Objectives –
1. To enhance the flow of powder.
2. To produce dust free formulations and produce uniform mixtures.
3. To improve compaction characteristics.
4. To eliminate poor content uniformity of mix.
5. To avoid powder segregation.
6. As Segregation may result in weight variation.
The process of granulation is further categorized into three classes based on use of binding
solutions,
1. Direct Compression
2. Wet Granulation
3. Dry Granulation

Step I –
1. Milling of the drug and excipients
2. Milling of the active ingredients, excipients etc. are milled to obtain a homogeneity in
the final granulation.
3. If the drug is given in solution then during drying it will come up to the surface.
4. To avoid this problem drug is mixed with other excipients in fine state.
Step II - Weighing
1. Weighing should be done in clean area with provision of air flow system.
2. In the weighing area all the ingredients must not be brought at a time to avoid cross
contamination.
Step III - Mixing or Blending
1. Double cone blender
2. V – blender
3. Ribbon blender
4. Planetary mixer
Any one of the blender may be used to mix dry powder mass.
1. Wet Granulation

Step IV – Wet Massing
Wet granulation forms the granules by binding the powders together with an adhesive.
Method
1. Drug + Diluents
2. Dry binders added
3. Blended uniformly
4. suitable solvent to activate the dry binder
5. blended in a Sigma - mixer or Planetary mixer till properly wet mass is formed.
Therefore, when;
1. Granulation is over-wetted, the granules will be hard, requiring considerable pressure
to form the tablets, and the resultant tablets may have a mottled appearance.
2. If the powder mixture is not wetted sufficiently, the resulting granules will be too soft,
breaking down during lubrication and causing difficulty during compression.

Step V – Wet Screening
Wet screening process involves converting the moist mass into coarse, granular aggregates by
1. passing through a hand screen (in small scale production) or,
2. passing through an oscillatory granulator of hammer mill equipped with screens having
large perforations (#6 – #8 mesh screen).
Purpose
1. Increase particle contact point
2. Increase surface area to facilitate drying.
Step VI – Drying
 Drying is usually carried out at 60°C.
 Depending on the thermolabile nature of the drug the temperature can be optimized.
 Drying is required in all wet granulation procedures to remove the solvent, but is not
dried absolutely because it will cause problems later on.
 Hence, certain amount of moisture is left within the granules, known as the residual
moisture.
Methods – Drying can be carried out in,
1. Tray dryers – it may take 24 hours of drying.
2. Truck dryers – the whole cabinet can be taken out of the dryer.
3. Fluid-bed dryer – carry out drying in 30 mins.

Step VII – Dry Screening
After drying, the granules are make monosize by passing through mesh screen.
Step VIII – Lubrication of granules
1. After dry granulation, the lubricant is added as a fine powder.
2. It usually, is screened onto the granulation through 60 or 100 mesh nylon cloth to
eliminate small lumps as well as increase the covering capacity of the lubricant.
3. The lubricant is blended very gently using tumbling action to maintain the uniform
granule size.
4. Too much fine powder is not desirable because fine powder may not feed into the die
uniformly causing variation in weight and density.
5. Since, the very nature of lubricant produce hydrophobic surface on the particle hence over
blending prevents the inter granule bonding that takes place during compression.
Step IX - Compression

It is followed in situations where,
 The effective dose of a drug is too high for direct compaction.
 If the drug is sensitive to heat, moisture or both, which precludes wet granulation.
 Eg, many aspirin and vitamin formulations are prepared for tableting by compression
granulation.
Steps of granulations
1. Milling
2. Weighing
3. Screening
4. Blending
5. Slugging
6. Granulation (Dry)
7. Lubrication
8. Compaction.
Purpose - To impart cohesiveness to the ingredients, so as to form tablets of desired properties.
Method - It is done either by,
1. High capacity heavy duty tablet press
2. Chilsonator roller compactor.
2. Dry Granulation

Advantages of Dry granulation over Wet granulation
1. No application of moisture (required in wet granulation) and heat (for drying).
2. So the drugs are susceptible to either moisture or heat or both can be made by dry
granulation.
3. Egs, calcium lactate cannot be used by wet granulation. (Aspirin, Vitamin C).
4. Dry granulation involves less steps and hence less time is required than that of wet
granulation.
5. Less steps requires less working space and energy.
6. Since popularity of wet granulation is more that dry granulation because former will
meet all the physical requirement for the compression of good tablets.

3. Direct Compression Method
Steps –
1. Milling
2. Weighing
3. Sieving
4. Blending
5. Compression
Advantages –
1. It is much more quicker than any of the previous process
2. Minimum number of steps are required.
 Modified diluents, binders etc. are available in the market which assure spherical shape of
the granules to modify flow property. However, they are not used extensively.
 If active medicament is less in amount then there will be no problem but in case of high
dose large amount of active ingredient is to be replaced by specially treated vehicles to
improve flow property or compressibility.

3. Compression
After the granulation, the processing of tablet is done under the compressor or compactor.
In this technique, when the powder flows from the hopper or feeder and comes between the
dye cavity and both the punches, a tablet forms.
Basic Component of Compression Machine
1. Head - Contain upper punches, dies, lower punches.
2. Body - Contain operating machineries.
3. Hopper - Holding feeding granules or powders.
4. Dies - Define size and shape of tablet.
5. Punches – For compression within dies.
6. Cam tracks – Guiding the movement of punches.
7. Feed frame - Guiding the granules from hopper to dies.
8. Upper turret - Holds the upper punches.
9. Lower turret - Hold the lower punches.
10. Die table - Contain the dies.
 Single station – Stamping press
 Multi - station – Rotary press

Tablet - Classification, Method of Preparation and Evaluation

Tablet machine’s output is regulated by three basic characteristic like,
1. No. of tooling sets
2. No. of compression station
3. Rotational speed of press.
Egs,
1. The monestry nova rotary tablet press. Gradually modification made in machines by
using hydraulic or pneumatic pressure to control pressure roll in place of spring for
smoother pressure.
2. Fette machine - Chill the compression (For low MP substance like wax)
3. Versa press - For multi layered tablet

4. Defects of Tablet
1. Capping - Capping is the partial or complete separation of the top or bottom crowns of a
tablet from the main body of the tablet.
Detection – Subjecting tablets to the friability test is the quickest way to reveal such problems.
Reason –
1. New set of punches and dies are very tightly fitted; i.e., the clearance is very negligible
hence air cannot come out.
2. Granules should not be completely dried. if over dried or under dried then capping may
take place.
Remedy –
1. Moisture content should be kept within 1 – 4%.

2. Cracking – Cracking is the removal of small flakes of tablet from upper and lower
central surface of tablet.
Detection – Subjecting tablets to HAO for very short duration.
Reason – Due to use of high molecular weight polymers.
Remedy – Use low molecular weight polymers and adjust the consistency of plasticizer and
pigment concentration.

3. Lamination – It is the separation of tablet into two or more distinct layers. Usually, these
problem are appeared immediately after compression, or even hour or days later.
Reason - Entrapment of excess air in the granules during compression. If the granules are
light and fluffy this type of problems are encountered frequently.
Remedy - Increasing the density of granules by adding more binder or changing the solvent of
binder.

4. Picking - When some portion of the surface of tablet is removed it is termed as picking.
Reason - When punch tips have engraving or embossing, usually of letters A, B, O are difficult
to manufacture cleanly. These may produce picking.
Remedies -
1. Lettering should be designed as large as possible, particularly on punches of small
diameter.
2. Plating of the punch faces with chromium produces smooth, non-adherent face.
3. Colloidal Silica is added as polishing agent that makes the punch faces smooth; so that
material does not cling to them.

5. Sticking - Sticking refers to tablet materials adhering to the die wall. Serious sticking at
ejection cause chipping.
Reason - Excessive moisture may be responsible for sticking.
Remedies –
1. Low melting point lubricant are replaced with high MP lubricants (Polyethylene glycol)
2. Low melting point substances, either active ingredients or additives may soften
sufficiently form the heat of compression to cause sticking.
6. Mottling - Mottling is an unequal distribution of color on a tablet, with light or dark
patches in an otherwise uniform surface.
Reason - Migration of water-soluble dyes to the surface while drying.
Remedies -
1. Change the solvent system and change the binder system
2. Reduce the drying temperature
3. Grind to a smaller particle size.
4. Use lakes instead of water-soluble dyes.

7. Orange peel effect – when the tablet have an
appearance of orange peel on the surface of tablet i.e., the
matte finish surface rather than the glossy look, it is called
as an Orange Peel Effect.
Reason – Poor management of tablet composition and
improper tablet coating.
Remedy – Mix the coating mixture properly.
8. Double impression – It will occur to the tablet when
the lower punch have the Monogram on it to give
impressions to tablets.
Reason – Free rotations of the lower punch after
compression causes a new lighter impression on the
bottom of tablet.
Remedy – By controlling or fixing the undesirable
movement of lower punches.

9. Poor flow and mixing – Poor flow of powder from hopper to die cavity which leads to
incomplete filling of die cavity and causes defected tablet punching.
Reason – Hopper vibration or unnecessary movement leads to segregation of powders.
Remedy – Addition of glidants or by the use of Induced feeders.
10. Weight Variation – Tablet batches will not have uniform weight.
Reason – Non uniform particle size distribution of particles of formula or presence of
excessive fine particles.
Remedies –
1. Use of proper concentration of glidants and lubricants.
2. Uniform size distribution of granules.
3. Decreasing proportion of fine granules by sieving.

Tablets Coating
The tablet coating is the procedure of polishing and preserving the tablet using various
polymers.
It is generally done to provide a proper finish to the tablet or to mask the unwanted and bitter
taste of drugs or to prevent the tablet from getting disintegrating in the stomach.
Reasons behind Coating of Tablets -
1. To mask the taste, odour or colour of the drug.
2. For improving the product appearance, particularly where there are visible differences in
tablet core ingredients from batch to batch.
3. To provide physical protection, facilitates handling, particularly in high-speed packaging
lines. ( Large scale production)
4. To provide chemical protection from its surrounding environment (air, moisture and light).
5. To control the release of drug from the tablet e.g. sustained release tablets.
6. To protect the drug from the gastric environment of the stomach with an acid resistant
enteric coating.

Components Considered in Tablet Coating
 Tablet Properties - Shape, Tolerance, Surface area.
 Tablet to be coated must possess the proper physical characteristics like spherical shape and
uniform surface.
 To tolerate attrition of tablets during coating process they must be resistant to abrasion and
chipping.
 As the tablet surfaces that are brittle and soften in presence of heat or effected by coating
composition and tend to become rough in the early stages of coating process are
unacceptable for film coating.
Coating composition – It involves polymers, color, plasticizer, solvent.

Types of Coating
1. Sugar Coating – It is done to mask the bitter taste of drugs and give it a bearable taste.
I. Sealing - To prevent moisture penetration into the tablet core, a seal coat is applied and To
strengthen the tablet core without a seal coat, the over wetted tablets would absorb excess
moisture, leading to tablet softening, and may affect the physical and chemical stability.
Ingredients -
Alcoholic solutions of Shellac (10 – 30% solid) or alcoholic solution of zein,
Alcoholic solution of cellulose acetate phthalate or polyvinyl acetate phthalate.
II. Sub-coating - To round the edges and build up the tablet size. Sugar coating can increase
the tablet weight by 50 to 100% at this step.
Method - The sub-coating step consists of alternately applying a sticky binder solution to the
tablets followed by a dusting of sub-coating powders and then drying.
Subsequent coatings are applied in the same manner until the tablet edges have been covered
and the desired thickness is achieved.

III. Smoothing (Syruping) - To cover and fill in the imperfections in the tablet surface
caused by the sub coating step.
Ingredients - Simple syrup solution (approximately 60–70%(w/w)). Often the smoothing
syrups contain a low percentage of titanium dioxide (1–5%) as an opacifier. This gives a very
bright and reflective background for the subsequent coloring step.
IV. Color coating - To impart an elegant and uniform colour.
Ingredient - Syrup (60 – 70% sucrose) containing the desired color.
Method - Syrup solutions containing the dyes are coated upto 60 individual applications until
the desired color is achieved. After each application of color, the coatings are dried. In the
finishing step a few clear coats of syrup may be applied.
V. Polishing - To produce the desired luster and uniformity on the surface of the tablet.
Ingredients - Mixtures of waxes (like beeswax, carnauba wax, candella wax or hard paraffin).
Method - Either this mixture of waxes is applied as powder or as dispersions in various
organic solvents in a polishing pan (canvas line pan).
VI. Printing - In order to identify sugar coated tablets often it is necessary to print them,
using pharmaceutical grade ink, by means of a process of offset rotogravure.

(B) Film Coating
Film coating adds 2 to 5% to the tablet weight. Film coating is a complex process that
involves the application of thin (in the range of 20-200 μm) polymer-based coatings to an
appropriate substrate (tablets, pellets, granules, capsules, powders, and crystals) under
conditions that permit,
1. Balance between (and control of) the coating liquid, addition rate and drying process.
2. Uniformity of distribution of the coating liquid across the surface of product being coated.
3. Optimization of the quality (both visual and functional) of the final coated product.
Advantages -
1. Substantial reduction in quantity of coating applied (2-4% for film coating, compared
with 50-100% for sugar coating).
2. Faster processing times and Improvement in process efficiency and output.
3. Greater flexibility in optimizing formulations as a result of the availability of a wide
range of coating materials and systems.
4. Ability to be applied a wide range of pharmaceutical products.

Tablet Evaluation or Quality Control Tests for Tablets
1. General appearance - Size, shape, and thickness. This is important to facilitate
packaging and to decide which tablet compressing machine to use.
2. Organoleptic properties - which include colour, odour and taste of the tablets.
3. Weight uniformity and Content uniformity - The tablet should contain the correct
dose of the drug.
4. Dissolution test - Drug should be released from tablet in a controlled and reproducible
manner.
5. Weight variation - The weight, size and appearance of the tablet should be consistent if
varies, it will be checked using weight variation test.
6. Hardness and Friability - The tablet should show sufficient mechanical strength to
withstand fracture & erosion during manufacture and handling.

1. Weight Variation
This test is based on the fact that, if the weight variation is within the limits then it can be
said that the amount of medicament will uniform considerably. Conversely, if the weight
variation is not in limits then it can be concluded that the active medicament will non
uniform considerably.
Sources of weight variation
Weight variation is solely dependent on the poor flow property of granules and filling of die
cavity. Poor flow properties arise from - (a) improper lubrication (b) size of granules (c)
adjustment of lower punch.
Weight variation test
The U.S.P. weight variation test is run by weighing 20 tablets individually, calculating the
average weight, and comparing the individual tablet weights to the average with the aid of
standard daviation. The tablets meet the USP test if “not more than 2 tablets are outside the
percentage limit and if no tablet differs by more than 2 times the percentage limit.”

2) Content Uniformity test
1. Weight variation test is applicable when the amount of medicament in the tablet is high.
2. In potent drug the medicament is less in amount in comparison to the other excipients.
3. The weight variation may meet the pharmacopoeial limitation but this will not ensure the
correct variation of potency. Hence, in this case the weight variation test is followed by
content uniformity test.
4. In this test 30 tablets are randomly selected for sample and at least 10 of them are assayed
individually according to the official assay method.
5. 9 of the 10 tablets must have potency within 15 % of the labelled drug content. Only 1
tablet may be within 25%.
6. If this condition is not met then the tablets remaining from the 30 must be assayed
individually and none may fall outside 15% of the labeled content.

3) Disintegration Test of Tablets
1. The time a tablet takes to disintegrate is the disintegration time.
2. To test the disintegration time one tablet is placed in each tube, and the basket rack
assembly is positioned in a 1-litre beaker of water, simulated gastric fluid or simulated
intestinal fluid, such that the tablet remains 2.5 cm from the bottom of the beaker.
3. A standard motor moves the basket up and down through a distance of 5 to 6 cm at a
frequency of 28 to 32 cpm (cycles per minute).

4) Dissolution Test
1. Disintegration test simply identifies the time required for the tablet to break up under
the condition of the test but it does not ensure the drug release in the bulk of the fluid.
Rate of dissolution is directly related to the efficacy of the drug. Rate of dissolution is a
good index for comparing the bioavailability of two tablet products of the same drug.
2. Apparatus-I (Basket)
3. In general, a single tablet is placed in a small wire mesh basket and immersed in the
dissolution medium (as specified in the monograph) contained in a 1000 ml flask at 37C.
Generally it is rotated at 50 rpm unless otherwise specified.
4. Apparatus-2 (Paddle)
5. The same equipment is used. Instead of basket a paddle is introduced as the stirring
element. The tablet is allowed to sink at the bottom of the flask before stirring.
6. Limit: A value of t90% (i.e., 90% drug release) within 30 minutes is often considered
satisfactory and is an excellent goal since a common dissolution tolerance in the USP/NF
is not less than 75% dissolved in 45 minutes.

5) Tablet Hardness - The resistance of the tablet to chipping, abrasion or breakage under
conditions of storage, transportation and handling before usage depends on its hardness.
Method - A tablet is taken between the 2nd and 3rd finger and pressing it with the thumb. If
the tablet breaks with a “sharp snap”, yet, it does not break when it falls on the floor – is said to
possess proper hardness.
Instruments used,
Monsanto Hardness Tester
Pfizer Hardness Tester
Erweka Hardness tester – Automatic
The hardness at which the tablet crushes is the hardness of the tablet.
Unit of hardness - Kg/sq.cm
Limit - Generally maximum 5 kg/cm.Sq hardness is required.

6) Friability
Tablet hardness is not an absolute indicator of strength since some formulations, when
compressed into very hard tablets may produce chipping, capping and lamination
problems. Therefore, another measure of tablet strength i.e. friability is often measured,
i.e. the friability.
Instrument: Roche Friabilator
Objective of friability test:
This apparatus is designed to evaluate the ability of the tablet to withstand abrasion, in
handling, packaging and shipping operation.
Method: 20 tablets, previously weighed are taken in the plastic chamber of the laboratory
friability tester. In the plastic chamber the tablets are subjected to abrasion and shock by
rotating the plastic chamber at 25 rpm for 4 mins (i.e. total 100 revolutions). The tablets
are dedusted and reweighed.
Limit: - For conventional compressed tablet the weight loss should be within 0.5 to 1.0 %.

Tablet - Classification, Method of Preparation and Evaluation

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