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Types Of tablets
Advantages and Disadvantages
Evaluation Of tablets
In 1843, a patent was granted to Thomas Brockedon (Englishman) for manufacturing pills
1980 nearly 300 monographs for tablets.
Over 2/3rd dosage forms are tablets.
Def: Tablets are flat or biconvex discs of unit dosage forms containing one or more active
ingredients, compressed along with necessary additives.
Types of tablets
Tablets Ingested Orally:
Compressed Tablets Or Standard Compressed Tablets.
• Both type of action – systemic effect and local effect.
•Rapid disintegration and drug release
•Mostly Antacids and adsorbents.
Multiple Compressed Tablets: For incompatible components these are:
either two layered (for two components) or three layered (for three components) tablet.
Tablets Ingested Orally
(2)Compressed coated Type:
•Compressed coated type- either tablet within a tablet or tablet within a tablet within a tablet. Tablet in this category are
usually prepared for two reasons
•1. To separate physically or chemically incompatible ingredients.
•2. To produce repeat action or prolong action product.
Compression coated tablets
Tablets Ingested Orally
Repeat Action Tablets :Sugar coated or multiple compressed tablets are usually coated with shellac or an enteric polymer so
that it will not release its drug in stomach but intestine.
Delayed Action And enteric coated Tablets
Delayed action tablets are intended to release the drug after some time delay or after passing the drug through the GIT.
Enteric coatings are applied mainly for drugs that are irritating.
Sugar coated tablet: Primary role is to produce an elegant, glossy, easy to swallow, widely utilized in preparing
Sugar coating doubled the tablet weight.
Now polymers are used with sugar solution.
Tablets Ingested Orally
Film Coated Tablets
•Advantage of film coated over sugar coated tablets is better mechanical strength and
flexibility of the coating, little increase in tablet weight.
•These are developed as an alternative procedure to the preparation of coated tablets in
which the drug is not required for coating.
•Easily administered for infants and elderly persons
•These are intended to be chewed in the mouth before swallowing. Used for large tablet
of antacid, bitter or foul testing drugs are not suitable for this type tablet.
Tablets Used In Oral Cavity
Buccal And Sublingual Tablets
•Drugs used by this route are for quick systematic action. The tablets are designed not to be disintegrate but slowly dissolve.
•Troches And Lozenges
These are mainly for treating soar throat and to control coughing in common cold.
These are designed to place in the empty
socket after tooth extraction.
Tablets Administered By Other Routes
To provide prolonged drug effects.
used for administration of growth hormone to food producing animal.
These are designed to undergo slow dissolution and drug release in vaginal cavity.
Tablets Used To Prepare Solutions
Tablets are designed to produce a solution
rapidly with the release of carbon dioxide.
Tablets are intended to be added to a given volume of water to produce a solution of a given drug concentration.
These tablets are composed of one or more drugs with water-soluble ingredients. Drug is added to sterile water
to prepare sterile solution, which is injectable.
– Large scale production at lowest cost
– Easiest and cheapest to package and ship
– High stability
User aspect (doctor, pharmacist, patient)
– Easy to handling
– Lightest and most compact
– Greatest dose precision & least content variability
– Coating can mark unpleasant tastes & improve pt. acceptability
Some drugs resist compression into dense compacts.
Drugs with poor wetting, slow dissolution, intermediate to large dosages may be difficult or
impossible to formulate and manufacture as a tablet that provide adequate or full drug
Bitter taste drugs, drugs with an objectionable odor, or sensitive to oxygen or moisture may
require encapsulation or entrapment prior to compression or the tablets may require coating.
Difficult to swallow in case of children and unconscious patients.
Ingredients used in tablet formulations
Diluents are fillers used to make required bulk of the tablet when the drug dosage itself is
inadequate to produce the bulk.
Properties Of diluents:
•They must be non toxic & physiologically inert.
•They must be free from all microbial contamination.
•They do not alter the bioavailability of drug.
Commonly used tablet diluents
Lactose-(anhydrous), spray dried lactose ,Directly compressed starch-Sta Rx 1500,Dicalcium Phosphate
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.
Example: Acacia, tragacanth, Cellulose derivatives-Methyl cellulose, Hydroxy propyl methyl
cellulose, Hydroxy propyl cellulose, Starch paste,e. t.c.,
To promote breakup of the tablets
To promote rapid release of the drug
Example: Starch- 5-20% of tablet weight, Starch derivative – Primogel and Explotab (1-8%) ,
Cellulose derivatives .
– To reduce the friction during tablet ejection between the walls of the tablet and the
walls of the die cavity
Example: Stearic acid, Magnesium stearate, Talc, PEG (Polyethylene glycols), Surfactants
– Reducing friction between the particles
– To improve the flow properties of the granulations
Example: - Corn Starch – 5-10% conc., Talc-5% conc., Silica derivative - Colloidal silicas
such as Cab-O-Sil, Syloid, Aerosil in 0.25-3% conc.
– To prevent adherence of the granules to the punch faces and dies.
Examples:-Talc ,corn starch ,metallic steroids.
Sweetening Agents: Sugar, mannitol. Saccharine (artificial): 500 time’s sweeter than sucrose
The use of colors and dyes in a tablet has three purposes:
•Masking of off color drugs
•Production of more elegant product
Example: FD & C yellow 6-sunset yellow ,FD & C yellow 5- Tartrazine
•These are mostly used in Chewable Tablets
•E.g. Flavor oils
Particle size & shape: Particle size of granulation affect the average tablet weight, weight
variation, disintegration time, friability, granule flow ability.
Dissolution of a drug depends on surface area of powder materials or
Density: Granule density may influence compressibility, tablet porosity, dissolution and other
Strength & Friability: Granules are aggregation of component particles that is held together
by bonds of infinite strength. Friability is the ability to formation of fines or fragments.
Flow properties: For the movement of granules from hopper to die cavity sufficient flow
properties are essential.
Angle of repose: It is maximum angle between the surface of a pile of powder and
Angle of Repose≤ 30 → Free flowing material
Angle of Repose ≥ 40 → Poorly flowing material
Hopper Flow rate: Granules are allowed to flow from the conical hopper onto a recording
balance device and dw/dt is calculated .
Raw materials → Weighing → Screening → Wet massing → Wet Sieving/Milling → Drying
→ Dry Screening → Mixing → Compression
The powder mass is wetted with the binding solution until the mass has the consistency of
If the granulation is over wetted the granules will be hard, if not wetted sufficiently, the
resulting granules will be too soft, breaking down during lubrication.
The wet mass is forced through a suitable sieve.
Moist materials from wet milling steps is placed on large trays and placed in drying chambers.
After drying granulation, the lubricant or glidants are added as fine powder to promote flow of
These granules then compressed to get tablet.
Raw material → weighing → Screen → Mixing → Slugging → Milling → Screening → Mixing
Compression granulation involves the compaction of the components of a tablet formulation by means
of flat punch. These compact masses are called slug and the process is called slugging.
Slugs are then milled and screened to produce a granular form.
Raw material → Weighing → Screening → Mixing →Compression.
This method is applicable for crystalline chemicals having good compressible characteristics and
flow properties such as: Potassium salt (chlorate, chloride, bromide), Sodium chloride, Ammonium
chloride, Methenamine etc.
Tablets are compressed directly from powder blends of the active ingredient and suitable excipients
No pretreatment of the powder blends by wet or dry granulation procedures is necessary.
A comparative processing chart of dif ferent
Compression: Compression is the process of applying pressure to a material with the help of a Tablet
Transitional repacking/particle rearrangement
Deformation at point of contact
Fragmentation and deformation
Inter molecular theory
Liquid –Surface film Theory
Single punch machine
The compression is applied by the upper punch making the single punch machine a
Multi-station rotary presses
• The head of the tablet machine holds the upper punches, dies and lower punches in place
• As the head rotates, the punches are guided up and down by fixed cam tracks, which control
the sequence of filling, compression and ejection.
• The portions of the head that hold the upper and lower punches are called the upper and
The portion holding the dies is called the die table
The pull down cam (C) guides the lower punches to the bottom, allowing the dies to overfill.
The punches then pass over a weight-control cam (E), which reduces the fill in the dies to the
A swipe off blade (D) at the end of the feed frame removes the excess granulation and
directs it around the turret and back into the front of the feed frame.
The lower punches travel over the lower compression roll (F) while simultaneously the
upper punches ride beneath the upper compression roll (G).
The upper punches enter a fixed distance into the dies, while the lower punches are raised to
squeeze and compact the granulation within the dies.
After the moment of compression, the upper punches are withdrawn as they follow the upper
punch raising cam (H).
The lower punches ride up the cam (I) which brings the tablets flush with or slightly above
the surface of the dies.
The tablets strike a sweep off blade affixed to the front of the feed frame (A) and slide down
a chute into a receptacle.
At the same time, the lower punches re-enter the pull down cam (C) and the cycle is
Single punch tablet machine (left) & 16 station rotary tablet machine(R)
Capping & Lamination: Complete or partial loss of top and bottom
crowns of a tablet from the main body is called capping.
The separation of a tablet into two or more distinct layers is called lamination.
Causes: Air entrapment , Deep concave punch ,Incorrect setting of the press ,
Compression of too dry material .
Remedy: By precompression ,Slowing Tableting ,Reducing final compression force ,
Using flat punch ,Using hygroscopic materials to maintain proper moisture level
eg. - PEG-4000 and Methyl Cellulose
Picking & Sticking: Surface materials from a tablet that is sticking to the punch and being removed from
the tablet surface is picking. Sticking refers to tablet materials adhering to the die wall.
Causes: Picking occurs when punch tips are engraving or embossing. Small enclosed areas in letters A.
Mottling: It is an unequal distribution of colors on a tablet with light and dark areas on tablet surface.
Cause: 1. Use of a drug whose color differs from tablet excipients
2. Use of a drug whose dehydration products are colored
Remedy: 1. The use of colorant
2. Disperse a dry colour additive during powder binding steps.
Weight Variation: Variation of tablet weight also causes variation of active medicament which change the
Cause: (a) Granule size & size distribution: Variations in the ratio of small to large granules and difference in
granule size determine the void space between particles are filled.
(b) Poor Flow: The die fill process in based on a continuous and uniform flow of granules from the hopper
through the feed frame.
(1) Arching or Bridging: Granules separate at the neck of the
hopper and flow stops completely..
(2) Rat Holling: In this case particles segregate near the
wall of the hopper and at the centre flow continues forming hole.
In rat holling flow rate decreases.
Addition of glidant can overcome these problems.
(c) Punch Variation: When length of lower punches is unequal, the fill in each die
varies which causes weight variations of tablet.
(d) Poor Mixing: Some times lubricants and glidants are not thoroughly distributed.
The flow of particles then impaired and the granules do not move efficiently into the
Hardness Variation: Hardness depends on the weight of materials and space
between upper and lower punch at the moment of compression.
Double Impression: This involves only punches that have monogram or engraving.
If the monogram present in upper punch, slight rotation of punch after
precompression produce double impression and vice versa.
Evaluation of Tablet
1.GENERAL APPEARANCE: The general appearance of a tablet, its identity and general
elegance is essential for consumer acceptance. The control of general appearance involves the
measurement of size, shape, colour, presence or absence of odour, taste etc.
Size & Shape: Tablet thickness can be measured by micrometer or by other device. Tablet
thickness should be controlled within a ± 5% variation of standard value.
Unique identification marking: These marking utilize some form of embossing, engraving or
printing. These markings include company name or symbol, product code, product name etc.
Organoleptic properties: Color distribution must be uniform with no mottling. For visual color
comparison compare the color of sample against standard color.
The presence of odour in a batch of tablet indicates a stability problem Presence of odour
could be characteristic of the drug (Vitamin), added ingredients (flavouring agent).
2.Weight variation test: weigh randomly 20 tablets individually in a batch.
Determine the average weight of 20 tablets.
Compare individual tablet weight to average weight
As per I.P. ,
If the tablet weight is, < 80mg , % deviation allowed up to 10%
> 80mg , % deviation allowed up to 7.5%
> 250mg , % deviation allowed up to 5%
If any of the tablet from the batch deviates from the above specifications,
another 10 tablets are selected from the same batch and the procedure is
repeated. Of 30 tablets , not more than 1 tablet should deviate.
3.Content uniformity test:
It is used to ensure that every tablet contains the amount of drug substance intended with little
10 tablets are assayed,
9 tablets should have % limit of 85-115%.
If more than 1 tablet deviates from 85-115%,
20 tablets are assayed
Not more than 1 tablet should have the % limit of 75-125%
4. Hardness test:
It is defined as the force required to break a tablet in a diametric compression test. Tablet
requires a certain amount of strength or hardness and resistance to friability to withstand
mechanical shocks of handling in manufacture, packaging and shipping
. Types of hardness testers are used.
Monsanto hardness tester .
Strong cob tester.
•. For, Conventional tablets hardness : 2.5- 5 kg/cm2
Dispersible/ chewable tablets hardness: 2.25- 2.5 kg/cm2
Extended release tablets hardness : 5- 7.5 kg/cm2
5. Friability test:
•. The instrument used is Roche friabilator.
•. It consists of a acrylic drum having 280-290mm diameter with a
thickness of 30mm. Acrylic drum is mounted on a horizontal axis
of a drive motor.
•. Drum is operated at a speed of 25rpm.&Allowed revolutions
for each tablet is 100.
Allowable range: loss 0.5 - 1% weight
Disintegration is the breakdown of tablet crust in to finely divided particulate matter or into
granules once the tablet is exposed to the gastric fluids .
Type of tablets
uncoated conventional tablets
sugar coated tablets
film coated tablets
Time Of disintegration
For enteric coated tablets:
Disintegration fluid for first 2hrs- 0.1NHcl.
After 2hrs, replace with 6.8pH phosphate buffer
Disintegration time – 60 min .
• For dispersible tablets:
Temperature – 22-240c
Disintegration time < 5min.
Uniformity of dispersion: place 2 tablets in 100ml of water and stirr gently .the
tablet should undergo dispersion within 5 min, which should pass through a sieve
screen of 22 mesh.
• For effervescent tablets:
Place one tablet in a 250ml beaker containing water, numerous gas bubbles are
Disintegration time- 3min.
Dissolution Test (U.S.P.): It is the solubilization of the drug or active moiety in to the dissolution
Different types of dissolution apparatus:
Apparatus -I-Rotating Basket type.
Apparatus -II- Rotating Paddle type.
Apparatus-3-Reciprocating cylindrical type.
Apparatus-4-Flow through cell.
Apparatus-5-Paddle over disk.
Apparatus-7-Reciprocating disc apparatus.
S1= 6 tablets are taken
S2=S1+6 tablets are taken
Acceptable: If all of the
Acceptable: If average of 12
tablets are not less than
tablets is ≥Q and no tablet is
less than Q-15%
If S1 fails
If S2 fails
S3= 12+12 tablets are taken
Average of 24 ≥ Q% not
more than 2 tablets should
be less than Q-15% and
None should be less than
The theory and practice of Industrial pharmacy, by Leon Lachmann and Herbert
.A.Lieberman,3rd edition. Page no: 294 to 336.
Pharmaceutical dosage forms tablet volume-1 edited by Herbert A.Liberman, Leon Lachman, and
Joseph B. Schwartz, page no:88 to 121.
Pharmaceutical dosage forms tablet volume-2 edited by Herbert A.Liberman, Leon Lachman, and
Joseph B. Schwartz, page no :201 to 211
Indian pharmacopoeia 2010 vol-2, page No: 751 to 754
The science and practice of pharmacy by Remington Volume I -905 to 916.