UNIT 2: TABLETS
According to PCI syllabus
• A tablet is a pharmaceutical oral dosage form (OSD).
• Tablets may be defined as the solid unit dosage form of
medicament or medicaments with suitable excipients and
prepared either by molding or by compression.
• It comprises a mixture of active substances and excipients,
usually in powder form, pressed or compacted from a powder
into a solid dose. The excipients can
include diluents, binders or granulating agents, glidants (flow
aids) and lubricants to ensure efficient
tabletting; disintegrates to promote tablet break-up in the
digestive tract; sweeteners or flavours to enhance taste; and
pigments to make the tablets visually attractive or aid in visual
identification of an unknown tablet.
• A polymer coating is often applied to make the tablet
smoother and easier to swallow, to control the release rate of
the active ingredient, to make it more resistant to the
environment (extending its shelf life), or to enhance the
• The compressed tablet is the most popular dosage form in use
today. About two-thirds of all prescriptions are dispensed as
solid dosage forms, and half of these are compressed tablets.
• Tablets are often stamped with symbols, letters, and
numbers, which enable them to be identified. Sizes of
tablets to be swallowed range from a few millimeters to
about a centimeter.
CHARACTERTICS OF TABLET:
• The tablet is an essentially tamperproof dosage form.
• They are unit dose form and offer the greatest capabilities of
all oral dosage forms for greater dose precision.
• Lightest and most compact of all oral dosage form.
• Their cost is low.
• Easiest and cheapest to package and shipping.
• Product identification is simple.
• Provide greatest ease of swallowing with the least tendency
for hang up, above stomach.
• They may be enteric or delay release.
• Better suited for large scale production.
• They have the best combination properties of chemical,
mechanical and microbiological stability than other oral
• Tablets have accurate dose.
Classification of Tablets:
1.Oral tablet for ingestion
1.Compressed tablet/standard tablet
2.Multiple compressed tablets
a. Layered tablet
b. Compression coated tablet
4.Sugar and chocolate coated tablet
5.Film coated tablet
6.Repeat action tablet
7.Delayed action and enteric coated tablet
8.Controlled release tablet
2.Tablet used in the oral cavity
1.Buccal and sublingual tablet
2.Troches and lozenges
3. Tablets administrated by other routes
1. Implants tablets
2. Vaginal tablets
4. Tablets used to prepare solution
1. Dry granulation
2. Wet granulation
1. DRY GRANULATION METHOD
a. Dry method of direct compression.
1. Crystalline substance like sodium chloride ,KCl,that may be
2. The compression of a single substance may produce tablet
that do not disintegrate.
3. The use of diluents with many moderate dose drugs makes
this process the most streamlined method of tablet
4. Direct compression material in addition to processing good
flow and compressibility, must be insert, tasteless, rework
able to disintegrate and inexpensive.
5. Some of the limitation to process are,
a. Difference in particles size and bulk density between
drug and diluents may lead to stratification within
granulation which ultimately leads to weight variation.
b. A large drug dose may lead problem with direct
compression if it is not easily compress itself.
c. In some case ,the direct compression diluents may
interact with drug.eg Amine compound reacts with
lactose gives yellow colouration.
d. Static charge produce during compression may prevent
uniform distribution of drug in the granulation.
1. It is a valuable technique in situations where the effective
dose of a drug is too high for direct compaction and the drug
is sensitive to heat ,moisture or both.
2. Many Aspirin and Vitamin formulations are prepared by
3. It involves the compaction of components of a tablet
formulation by means of a tablet press or specially designed
machinery, followed by milling and screening prier to final
compression into a tablet.
4. The masses formed where the initial blend of powers is
forced into dies and is compacted by means of flat-faced
punches are called slugs and process as slugging.
5. Slugs are then screened or milled to produce a granular form
6. Slugging in just an elaborate method of subjecting material
to increased compression time.
7.Two or more times that the material is subjected to compaction
pressure causes a strengthening of bonds that hold the tablet
together and the resultant granules also increases the fluidity
of powder mixture.
8.This method requires less equipments and space than other
9.On large scale, compression granulation can be performed on a
special designed machine called a roller compactor , which
can produce as much as 500kg/hr or more compacted ribbon
2. Wet granulation
1. The unique portion of wet granulation process involves the
wet massing of powders, wet sizing or milling, and drying.
2. Wet granulation focus on the granules by binding the
powders together with an adhesive, instead of by
3. The wet granulation technique employs a solution,
suspension or slurry containing a binder which is usually
added to the powder mixture.
4. The liquid bridges are developed between particles and
tensile strength of bonds increases.
5. Once the granulating liquid is added, mixing continues until
a uniform dispersion is attained and all binders are activated.
6. As the liquid content increase it gives rise to funicular state.
7.Then the capillary state is reached in which the void
spaces within te granules are entirely eliminates.
8.Further addition of liquid results in droplets
9.The liquid plays a key role in the granulation
10.Once granulating liquid has been added mixing
continued until a uniform dispersion is attained and
all the binder has activated.
11.During granulation particle and agglomerates are
subjected to consolidating force by action of
machine parts and of intraparticulate force.
12.A rough way to determine the end point is to press
a portion of mass in the palm of hand.
13.The next step is wet screening process involving converting
the moist mass into coarse granular aggregates by passing
through hammer mill or oscillating granulator.
14.The purpose is to increase particle contact point increase
surface area to facilitate drying.
15.A drying process is required in all wet granulation procedures
to remove the solvent.
16.After drying the granulation is screened again.
17.Ovens employed for drying granulation wetted with
explosive solvents should employ high airflow rates.
It is done for 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 acid resistance enteric coating
5. To incorporate another drug or formula adjuvant in the
coating to avoid chemical incompatibilities or to provide
sequential drug release.
6. To improve the pharmaceutical elegance by use of special
colors and contrasting printing.
• Sugar coating process involves several steps, the duration of
which ranges from a few hours to a few days.
• A successful product depends on the skill of the coating
• The basic sugar coating process involves the following
• 2.Sub coating
• Since sugar coating tends to be long and vigorous , the cores
should be relatively resistance to breakage , shipping and
1. To prevent moisture penetration into the tablet core a seal
coat is applied.
2. In pan ladling processes, without a seal coat, the over wetted
tablets would absorb excess moisture, and affecting the
physical and chemical stability.
3. Shellac is an effective sealants.
2. Sub Coating:
• The sub coating is applied to round the edges and build up the
• Sugar coating can increase the tablet weight by 50% to 100%
• Sub coating step consists of alternately applying a sticky
binder solution to the tablet followed by a dusting of sub
coating powder and then drying.
• Sub coating are applied until the tablet edges have been
covered and the desired thickness is achieved.
• The control of drying rate is critical to obtaining a rapid
application of the sub coat
3. Syruping (smoothing):
1. The purpose of this step is to cover and fill in the
imperfections in the tablet surface caused by the sub
coating step, and to impart the desired color to tablet.
2. The first syrup coats usually contain some suspended
powders and are called grossing syrup.
3. Then the syrup solutions containing dye are applied
until the final size and color are achieved.
4. In the final step, a few clear coats of syrup may be
4. Polishing and Finishing:
1. The desired luster is obtained in this final step of sugar
2. The tablets can be coated in the clean standard coating pans,
or canvas lined polishing pan, by carefully applying
powdered wax or warm solution of these waxes in naphtha
or suitable volatile solvents.
DEFECTS OF COATING:
Variation in formulation and processing conditions may results
in unacceptable quality defects in film coating.
They are as follows:
1. Sticking and picking
3. Orange peel effects
4. Bridging and filling
6. Hazing/Dull film
7. Color variation
1. A rough or gritty surface is defect often observed in spray
2. Some of the droplets may dry too rapidly, resulting in
particle deposition on the surface which leads to roughness.
3. Moving the nozzle closer to the tablet or reducing the degree
of automization can decrease the roughness due to spray
• When a coated tablet require further drying in oven, too rapid
evaporation of the solvent from the core and the effect of high
temperature on the strength, elasticity and adhesion of the film
may result in blistering.
3]Sticking and picking
1. Over wetting or excessive film tackiness causes tablets to
stick to each other or to the coating pan.
2. On drying, a piece of the film may remain adhered to the pan
or another tablet.
3. A reduction in the liquid application rate or increase in the
drying air temperature and air volume usually solves this
4] Orange Peel effects:
• Inadequate spreading of the coating solution before drying
causes a bumpy or orange peel effect on the coating.
• This indicates that spreading is impeded by too rapid drying or
by high solution viscosity.
• Thinning the solution with addition solvent may correct this
5] Color Variation:
1. This problem can be caused by processing conditions or the
2. Improper mixing, uneven spray pattern and insufficient
coating may result in color variation.
3. The migration of soluble dyes, plasticizers and other
additives during drying, may gives the coating a mottled or
4. The use of lake dyes eliminates the dye migration.
1. Cracking occurs if internal stresses in the film exceed the
tensile strength of the film.
2. The tensile strength of the film can be increased by using
higher molecular weight polymers or polymer blends.
QUALITY CONTROL TEST
• This test is run to monitor the process including test for tablet
weight, weight variation, hardness, thickness, disintegration
• The data supplied by the formulator is usually employed by
quality control personnel to establish the test limits.
• The quality control tests for tablets are:
1. General appearance
2. Size and shape
4. Organoleptic properties
6. Drug content and release
7. Weight variation
8. Content uniformity