Title 2: Tablets

Prepared by
Dr Allan (Amooti) AHIKIRIZA (MPS)
Bpharm, Mpharm pharmaceutics

Pharmacy Students' Lecture

 TABLETS

INTRODUCTION
• Pharmaceutical tablets are solid unit dosage forms, prepared by compressing or moulding
a drug or a mixture of drugs, with or without diluents.

• Tablets may be defined as the solid unit dosage form of medicament or medicaments
with suitable excipients and prepared either by moulding or by compression
Properties of a tablet
• Ultimately finished products should have the same Content
uniformity, weight, size, appearance, diameter, disintegration and
dissolution time.
• All these parameters should be within the quality control limits
Properties of powder
• Fluidity – the powder should flow freely through the hopper during
processing to avoid weight variation
• Compressibility- the powder should be able to withstand pressure
application during compression. Compressibility can be improved by
addition of lactose or by granulation
 Classification of tablets
There are four different ways to classify tablets and these include:

1. According to use, here tablets are grouped as; for oral administration, tablets for use in oral activity, tablets
for solution preparation, and tablets for administration by other routes.

2. According to shape, here tablets can be concave or convex tablets, core tablets, layered etc.

3. According to modified release action ( timed release, sustained release, prolonged release) and delayed
action tablets like enteric coated tablets for example bisacodyl.

4. According to the method of manufacture, that is either compressed, moulded or modified tablets.
Tablet excipients
What are tablet excipients?
• Excipients are majorly used to achieve
• 1. For the tablet to disintegrate when so required and in the predetermined
time frame
2. To increase the bulk of the tablet such that it is possible to manufacture it(some
tablets contain as little as 0.05 mg of active ingredient)

NB: most excipients are multifunctional

Those that help to impart satisfactory processing and compression properties to the
formulation and
Those that help to give additional desirable physical characteristics to the
compressed tablet.
 Excipients cont..
Type Purpose Example

Diluents / fillers Make tablet bulk Lactose ,starch, dicalcium phosphate,

dextrose

Adsorbents Adsorb oil Magnesium carbonate, kaolin,mcc

Moisturizing agents Use in wet granulation Methylated spirit, water, isopropyl

alcohol

Binding agents Make hard and strong Sucrose, starch, mucilage paste,mcc

Lubricating agents Prevent adherence to punch, ensure Talc, magnesium stearate

smooth ejection, enhance flowability

Glidants Reduce inter-particulate friction Colloidal silicon dioxide

 Excipients cont…
Disintergrants Release drug into the system Dry starch, sodium starch glycolate
Colorants Used for branding
Flavors Mask unpleasant taste

* Mcc – microcrystalline cellulose

Excipient properties
• Should be chemically inert
• Non hygroscopic
• Biocompatible with other ingredients
• Cheap
• Acceptable taste and odour
Tableting methods
• There are three methods: direct compression, dry granulation and
wet granulation
• Before choosing a method consider:
1. API form- is it crystalline, granular, amorphous
2. Moisture sensitivity of ingredients
3. Binding characteristics
4. Flow characteristics
5. Color requirement
 Tablet Manufacturing Equipment/ Machines
1. Size reduction equipment/ communition equipment
2. Weighing balance/ balances
3. Mixing equipment
4. Granulators
5. Dying equipment
6. Tabletting machine
7. Quality control equipment
8. Coating and polishing machines for coated tablets
9. Packaging machines
Direct compression
• This method is easy, cheap, requires less labour
Weigh API + excipients

Screening

Mixing

compression
Dry granulation
• Weigh API + excipient • Sizing

• Screening • Screening

• Mixing () • Binders & disintergrants

• Binders & disintegrants • Lubricants

• Slugging • Mixing

• Slug crushing • compression

Dry granulation cont..
• NB: sizing is done using sieves. NB: A sieve number
• The first addition of binders and disintegrants ensures tablet
dissolution while the second addition ensures tablet disintegration

• Lubrication is done at the end to ensure the material flows freely

through the hopper into the die
oooooo Disintegration (Separation into component parts)
ooo

:::::::: Dissolution (The process of going into solution)

Wet granulation
• Weigh API+ excipient • Drying

• Mixing • Crushing

• Wetting • Sizing

• Mixing • Lubrication

• granulation • Mixing

• compression
Tableting machine
• The final powder flows into the die through the hopper,
once in the die, the powder is compressed by the upper punch moving
down and the lower punch moving up,
after compression the upper punch moves back up and the lower
punch moves up a short distance in order to eject the compressed
tablet
Tablet machine cont..
• There are two types of machines:

1. the single-punch machine

2. the multiple punch machine which can be either single station or

double station.
 Stages in tableting
1. Die filling- powder moves through the hopper and fills the die

2. Tablet formation – the upper punch descends and enters the die to apply
pressure on the powder till a tablet is formed, the lower punch can be
stationery or it can move upwards in the die. the upper punch then moves
back up

3. Tablet ejection- the lower punch rises to the level of the top of the die and
the tablet is removed by a pushing device
 Processing problems
Processing problems can occur due to bad formulation or bad equipment.
1. Capping – the upper or lower surfaces of a tablet separate due to air
entrapment, plastic deformation of particles or too much pressure applied
at a go. To avoid this first apply little pressure, release then apply the
required pressure

2. Lamination – separation of a tablet into two or more distinct layers from the
center. When granules are too dry, they lack cohesion and they do not bind
well. To overcome this moisture should be controlled between 3%-5%
• Lamination can also be due to a lack of proper judgment of the lower punch
and sweep off blade
 Problems cont..
3. Picking – part of the material is removed from the tablet and it adheres to the
punch face, especially the upper punch during engraving it is therefore better to
use bigger letters and avoid full words

4. Sticking – this is when the tablet or part of the tablet material adheres to the
die. This can be solved by adding diluents to increase tablet size.
Another cause of sticking is low melting point ingredients, when heat is
generated during compression the contents melt and stick to the die

5. Cracking – the appearance of small fine cracks on the lower, upper or sides of
the tablet mostly due to very large tablets or use of biconcave dies. To avoid this
use flat dies
 Problems cont..

6. Chipping - this is the breakage of the edges of the tablet due to use of too
much binder or too dry granules

7. Double impression – is due to free rotation of the punch especially the lower
one during ejection.

8. Mottling – unequal distribution of color where the tablet has some light and
dark patches
 Factors influencing tablet parameters
Parameter Factors

Weight variation Poor flow due to less or poor mixing of lubricant, die size
variation, machine speed, ratio of fine particles:
grains(25:75),

Hardness Less binding agent, less pressure, less number of grains

Friability Less binder, moisture level, lack of grains

Thickness Lack of grains, grain size

Factors affecting disintegration
1. Binder – too much ↑ disintegration time
2. Type of lubricant – hydrophilic ↓ dissolution time, hydrophobic ↑
dissolution time
3. Mixing time of lubricant - poor flow ‹5-10min› ↑ dissolution time
4. Disintegrants – the more the disintegrant the ↓ dissolution time
5. Diluents – e.g. sorbitol is slow dissolving, calcium salts are fast
dissolving
6. Grain size – smaller size = ↑ surface area hence ↓ dissolution time
 Tablet coating
• This is the application of a coating material to the exterior of a tablet with the
intention of getting one or more of the following benefits:

1. To make them elegant

2. To mask bad taste
3. To make them easy to swallow
4. To add batch difference so that ingredients of different colors are not visible
5. To prolong time of action
6. To improve stability by protecting them from light and moisture
7. For branding purposes
Coating process
• Tablets are spread on a pan or fluid bed that is continuously being
agitated, the coating solution is sprayed on the tablets and passing
hot air immediately evaporates the liquid portion of the coat leaving
the coated tablet dry
 Sugar coating
• Involves the following steps:
1. Sealing of the tablet core with water-impermeable polymers e.g. zein (corn protein) to
prevent moisture penetration

2. Subcoating is done to round the edges and increase tablet weight. it is done using
sucrose syrup, calcium carbonate, talc or acacia gum

3. Syrup coating/smoothing is done to cover up imperfections on the tablet surface and

achieve a predetermined size. This is achieved by applying a few coats of sugar solution

4. Coloring – apply coloring solution

5. Polishing – is done using bees wax to give tablets a shinny finish.

6. Printing - logo is added if desired using laser

 Film coating
• Involves deposition of thin film polymers around the tablet by spray method.
the choice of polymer material depends on the desired site of release of the
drug or the desired release rate

Examples
• Hydroxy propyl methyl cellulose
• Methyl hydroxy ethyl cellulose
• Ethylcellulose
• Povidone
• Cellulose acetate phthalate
 Characteristics of a film coat
• Should be soluble in a solvent of choice
• Should have an elegant finish
• Should be stable in light, heat and moisture
• Should be of agreeable odour, taste and colour
• Should be pharmacologically inert
• Should be non-toxic
• Should be compatible with coating additives
 Types of film coating
• 1. Aqueous film coating – this is done using water as a polymer solvent. It
is always preferred as it is cheaper, safer and readily available

• 2. Organic film coating - done for polymers insoluble in water. The organic
solvents include methanol, dimethyl chloride.

Disadvantages of organic solvents-they are costly, flammable, toxic

 Material for film coating
1. Polymers
• should be water soluble to enhance tablet dissolution

• Viscosity should be low for a given concentration to allow easy spraying

• Should not be permeable to prevent humidity and moisture penetration

• Should have mechanical strength

 Materials cont..

• 2. plasticizers are used to increase plasticity e.g. diethyl phthalate

• 3. coloring agents – water soluble coloring agents are used e.g. iron
oxide, titanium dioxide

• 4. polishing agent e.g. silicon dioxide

 Processing parameters
1. Inlet temperature
2. Bed temperature
3. Relative humidity
4. Liquid spray rate
5. Droplet size
6. Drying time
7. Pan speed
8. Distance of spraying nozzle to bed
 Enteric coating

• Is usually thicker than film coating and it is important for drugs that are
destroyed by stomach acid and those that irritate the GIT.

• Polymers used here should be insoluble in aqueous media at low Ph.

• Examples
cellulose acetate phthalate
Polyvinyl acetate
Acrylic acid derivatives
shellac
 Disadvantages of Tablet Coating
 Tablet coating process is tedious and time-consuming
 The process increases the cost of formulation
 Tablet coating may interfere in the pharmacodynamic
properties of drug formulation
 The process may sometimes result in various coating defects
like chipping, cracking etc.
 The process remained complicated and thus requires the
expertise of highly skilled technician.
Quality control tests
1. General appearance – the following parameters should be checked:

• Elegance • Surface texture

• Shape • Identity
• Size • Odor
• Colour • Taste
Drug content tests
• 1. Weight variation-
Average weight Deviation allowance
≤ 130 mg 10%
130mg – 329mg 7.5%
≥ 329mg 5%

Weigh 20 tablets, not more than two tabs should be defective and the
defect should not be more than twice the deviation allowance
 Drug content tests cont..
2. Assay - grind 20 tablets and extract their active ingredient
• Analyze the actives using a U.V spectroscopy, HPLC etc.
The deviation allowed is 90% - 110%

3. Content uniformity – select 30 tablets, first assay 10 tabs,

the actives in 9 of these should be between 85% - 115%.
The 10th tablet is allowed 75% -125% but if this is not met,
assay the remaining 20 tabs and they should all be within 85%- 115%
 Disintegration time
• Make an assembly of 6 glass tubes with a mesh # 10 at the bottom of the
tubes, tubes are open at the top.

• The assembly is suspended in a beaker containing 1 L of water and is moved

up and down to cover a distance of 5-6cm at a rate of 28-32 moves per
minute.

• When moved down it must be 2.5 cm above the bottom and when moved
up it must be within the water level
 Disintegration cont..

• Record the time taken for the entire tablet to dissolve and pass
through the mesh in all 6 tubes as the disintegration time.

• Uncoated tablets should take approximately 2.5-10 minutes

• Enteric coated tablets should not disintegrate within the first hour
as they usually take 2-3 hours in the intestinal fluid.
Read and make notes about
• dissolution test
• Compatibility testing of excipients and API

• (Class) Draw and label a single punch tabletting machine

• Class (Draw a multi-punch tableting machine both single and double

station)