INTRODUCTION:
Coated tablets are defined as “tablets covered with one or more layers of mixture of various substances such as substances such as
- Natural Or Synthetic Resins
- Gums
- Inactive And Insoluble Filler,
- Sugar
- Plasticizer
- Polyhydric Alcohol
- Waxes
- Authorized Colouring Material and Flavoring agent
The first coated pills were used by Rhazes (850-923). Sugar coating of pills was extensively developed by Frenchmen. Then a dramatic change was observed in coating when Abbot laboratories marketed first film coated tablet. Dr. Dale Wurster develop air suspension coating technique in 1950s.
Tablet coating is one of the oldest pharmaceutical processes still is existence. 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 over uncoated variety. It involves application of a sugar or polymeric coat on the tablet. The advantages of tablet coating are taste masking, odor masking, physical and chemical protection, protects the drug in the stomach, and to control its release profile. Coating may be applied to a wide range of oral solid dosage form, such as particles, powders, granules, crystals, pellets and tablets. When coating composition is applied to a batch of tablets in a coating pan, the tablet surfaces become covered with a tacky polymeric film. There are several techniques for tablet coating such as sugar coating, film coating and enteric coating. The disadvantages of the older techniques of coating have been overcome with the recent advancement in coating technologies. In these technologies coating materials are directly applied on the surface of the tablet without the use of any solvent. ICH guidelines also prefer the avoidance of organic solvents in pharmaceutical dosage formulations considering products safety profile. This review discusses the basic concepts of tablet coating, the recent advancements made, the problem faced during the process, their solutions and coating evaluation.
Coating
for Consumers:
Patient compliance is affected
by a product’s :
Ease of Use
·
Identity
·
Efficacy
·
Taste
·
Odour
Reasons for Coating
Different dosage forms may need different kind
of coating formulation, technique and process. Therefore a formulation
development scientist has to understand the critical aspects associated with
each case. Different dosage forms which can be coated are: tablets, capsules, pellets,
granules, particles and powder. All the above mentioned dosage forms may need
coating for different reasons such as:
1. Change in appearance: To impart colour for easy identification during manufacture,
dispensing, in use by patient and brand image building.
2. To eliminate dust generation: To reduce handling problems and to reduce dust induced toxicity.
3. Taste masking: Mask
the bitter or unpleasant taste.
4. Odour masking: Mask the unpleasant odour of active ingredients like vitamins,
antibiotics etc.
5. Isolation of incompatible materials: Some of the ingredients may be incompatible to
each other, and these can be separated by putting a barrier coating in between them.
6. Protection from environmental conditions : Some of the ingredients may not be stable in
the presence of moisture, light, oxygen etc. The product stability can be
improved by coating.
7. Change in release characteristics: Drug release profile from the dosage form can be
tailored by coating techniques for example – delayed release (by enteric coating),
extended release (by semi permeable membrane coating or mixing of pellets which
are coated to various degree or with different coating materials).
8. To improve appearance: often where the core tablet is of poor colour or shows mottling.
Three basic components are critical in Tablet
coating.
1.Tablet properties
2.Coating process
1. Coating Equipment
2. Parameters of the coating process
3. Facility and ancillary equipment
4. Automation in coating process.
3.Coating compositions
1. Tablet Properties
Tablets that are to be coated must possess the
proper physical characteristics. In the coating process, the tablets roll in a coating
pan or cascade in the air stream as the coating solution is applied. The
tablets must not chip or break.. Also the tablets
are exposed to elevated temperature and humidity
during the coating. The tablet surface which are brittle gets soften in the presence
of heat or effected by coating solutions tends to become rough in the early
phase of the coating process are unacceptable for coating, especially for film
coating which deposits thin layer of coating, while sugar coating can fill the surface
imperfection but upto some extent because of their high solid contents. The
tablets must be robust enough to withstand
these conditions.
The following must be considered while designing tablets which are
to be coated.
1. Tablet Hardness: tablet breakage is typically seen when the hardness is inadequate
a rule of thumb is the tablets to be coated should have hardness not less than
8 kp (11.2 scu, 80 N)
2. Tablet Friability: Friability is more important as that of hardness. This test
accurately reflects the stresses that the tablets will when tumbling in a coating
pan. The maximum recommended friability for tablets to be coated is 0.5%
however for best results the aim should be 0.1%. If the friability is above
this limit the tablets may cap, laminate or abrades during coating process.
3. Tablet core shape: Tablets may be compressed in variety of shape that include;
Round/oblong flat, round/oblong shallow concave, round/oblong standard concave,
round/oblong deep concave. The flat faced tablets have overall best surface
hardness buit tend to be brittle at the edges, these tablets are not good for
coating because of twinning problem.
The deep concave type good mixing and no
twinning problem but they offer the lowest level of surface hardness, so these
are also not suitable because of high attrition at crown. The best compromise
between surface hardness, mixing and twinning is offered by the normal or
shallow concave shapes and these are recommended for coating.
Generally the flat faced, shallow concave or
capsule shaped tablets show greatest erosion at the edges while deep concave
show erosion at the crown.
4. Tablet porosity: increased tablet porosity can be beneficial in increasing the
force of adhesion between the tablet surface and the applied coat. It should be
kept in mind increase porosity comes at the sacrifice of tablet hardness.
5. Tablet core ingredients: The ingredients both active and inactive can have significant
effect on the interaction between the substrate and coating. The most important
is the degree of adhesion. The active ingredient is often present in
significant amount in the tablet formulation, this will overwhelm the influence
on adhesion by other ingredients. If the active content is low and it has
negative impact on film adhesion, this may be neutralized by selection of
proper excipient. Lubricants are added to tablet formulations to minimize both
die wall friction and punch adhesion, lubricants results in decrease of tablet
hardness and coating adhesion, specially when metal (magnesium) stearates are
used in combination with MCC and starch based excipients.
Superdisintegrants are valuable materials in
tablet formulation due to their ability to reduce disintegration time and
increase dissolution rate. However if used indiscriminately, they can exert
negative effects on other aspects of tablet quality. High levels of
superdisintegrant may result in orange peel effect though the hardness and
friability will be well in the limit.
Coating Process:
Tablet coating is the application of coating
composition to a moving bed of
the tablets with concurrent use of heated air to
facilitate evaporation of
Equipment: The process and equipment must provide;
1. Distribution of the liquid coating formulation over the whole of
the available tablet surface (ladling, Spraying).
2. Continuous mixing of the tablet load in order to achieve an evenly
coated product (rotation).
3. Continuous drying to solidify the film quickly (hot air).
4. Removal of solvent vapour (plus dust generated, plus used drying
air and atomizing air).
Equipment:
Three types of coating equipments are used.
·
Standard
(conventional) coating pan
·
Perforated
coating pan
·
Fluidized
bed (air suspension) coater
1. Standard (conventional) coating pan
Pellegrini pan
Pellegrini system has baffled pan and a diffuser
that distributes the drying air over the tablet bed surface.
Immersion sword pan
In this system the drying air is introduced
through a perforated metal sword
device that is immersed in the tablet bed. The
drying air flows upward from
the sword through the tablet bed thus providing
efficient drying of the wetted
tablets.
Immersion Tube pan
In this system a tube is immersed in the tablet
bed. The tube delivers the
heated air, a spray nozzle is built in the tip
of the tube to deliver the
coating composition. The coating solution and
dry air introduced at the
same time.
Perforated pan system
This system make use of perforated or partially
perforated drum (pan) that rotates on its horizontal
axis in an enclosed housing. This type of coating system are more efficient in drying as compared to the
conventional system. With such system mark
decrease in coating time can be achieved. The current systems available include;
1. Manesty Accela Cota
2. Freund Hi-Caoter
3. Driacoater
4. Glatt Coater
Fluidized bed (air suspension) Coater
This system uses columnar chamber through which
high volume heated air is supplied from the
bottom to fluidize the tablet bed, providing the medium for drying and the energy for mixing. These are most
efficient drying and mixing
equipment. These are not commonly used for tablets on large scale high attrition the tablets chip, breaks, abrades
out. This system is commonly applied
for particulate coating (microencapsulation and pellet coating).
The coating solution is either applied from the
bottom (Wurster) or from the top of the chamber on
to the tablet bed.
Spraying Application Systems (spray gun):
Two systems are used to apply atomized spray of
coating composition onto
the tablets.
1. High pressure air less system
2. Low pressure air atomized system
1. High pressure air less system
In this system the liquid is pumped at high
pressure (250-3000 psig) through a small orifice (0.009-0.20
inch) in the fluid nozzle. The degree of atomization and the spray rate are controlled by the fluid pressure, orifice
size, and viscosity of the liquid.
The disadvantage of the system is that, Because of the small orifice the suspension may
block it therefore the coating suspension may be
finely milled or filtered. The airless system doesn't
provide independent control of suspension application rate, degree of atomization and spray fan width.
2. Low pressure air atomized system
In this system liquid is pumped through larger
orifice (0.020 – 0.06 inch) at relatively low pressure (5-50 psig). Low
pressure of about 10-100 psig at the atomizer tip contact the liquid and
disperse it in finely divided spray. In this system atomization can be
controlled independently of the operating pressure, also fan width can be controlled.
Coating Parameters
During coating the tablets move through an
application zone in which a portion of the tablets receive some coating. Most
of the time tablets are in drying mode moving away from the application zone
and recycled repeatedly through the application zone. In the coating operation (continuous)
an equilibrium is maintained between coating composition application rate and
the rate of evaporation of the solvent. Deviation from this equilibrium results
in serious coating problems. These two parameters can be adjusted by;
Spray Gun position: 6-18 inches from the bed, 450 angle to the
tablet bed. Not overlapping fan width nor to far.
Effect of pan load: under loading the pan will result in situation
where the tablet does not cover fully the exhaust plenum, and the majority of
the drying air stream will bypass the tablet bed and drying efficiency will be low.
Air volume and temperature: Drying is controlled by the quantity and temperature
of the drying hot air, and the quantity of exhaust air. It is important to
balance the inlet and exhaust air flow rates such that there is slight negative
pressure in the chamber. Also the temperature difference between the inlet and
exhaust must be with in 20-30oC. It is important to monitor the following three
temperatures.
1. Inlet Air temperature
2. Tablet Bed temperature (most critical)
3. Exhaust air temperature
4. Coating composition: coating
composition contains the ingredients that are to be applied on the surface of
tablet and the solvents , which act as carrier for the ingredients. These
solvents are not required in the final product and must be removed. A balance
must be established between the coating composition flow rate and the three
drying variables (drying air temperature.
Types of coating
1.Sugar coating
2.Film Coating
1. Conventional film coating
2. Enteric film coating
Film coating on the basis of solvent system
1.Organic coating
2.Aqueous coating
Sugar coating
This involves several steps, the duration of
which ranges from few hours to few days. The quality of coating depends upon
the skill of the operator specially in ladling type of solution application.
The sugar coating results in elegant highly glossed finished tablets. Following
steps are involved in sugar coating.
1. Sealing
2. Subcoating
3. Syruping (smoothing)
4.Finishing
5.Polishing
1. Seal coating (sealing)
To prevent moisture penetration into the tablet
core a seal coat is applied. This is specially required in pan-ladling process,
to avoid overwetting of the tablet bed. Without seal coat the tablets will
absorb sufficient moisture to be softened or disintegrate , effecting the
physical appearance. Shellac is the most commonly applied sealant agent, but it
offers the problem of increase the disintegration and dissolution time on aging
because of polymerization of shellac. Zein is also used as sealant, it has no
problem as associated with the shellac. The process description is Pan Speed 10
rpm
Supply air temperature 30°C, 3 application of
800 ml of sealant solution is applied and the tablets are allowed to dry for
15-20 minutes between the application. If the tablets become tacky at any time
apply sufficient talc to avoid sticking.
2. Sub Coating
This is applied to round the edges and build up
the tablet size. Sugar coating results in the increase of tablet weight by
50-100%. Usually gelatin/acacia solution is used along subcoating powder. The
process description is Pan speed 10 rpm Turn heart and inlet air off. Use
exhaust air only apply 3-9 coats. Use 1-2 liters for first coat and then
reduced the quantity accordingly to obtain the required weight and round edges.
Allow the tablets to dry at least for 20 minutes after each application. Dust
with subcoating powder at the end. After the
last coat, jog the pan for at least 2-4 hours to ensure complete dryness.
3. Syrup (smoothing/color) coating
The purpose of this step is to cover and fill
the imperfection in the tablet surface caused by subcoating, this is the most
technical step as it requires the most skill. This step usually involves three
basic phases.
1. Grossing syrup (a syrup with subcoating powder dispersed in it):
Process outline is Remove excess dust from the
pan. Turn on the exhaust air. Adjust the temperature to achieve the exhaust air
temperature of 45-48oC. Pan Speed 15 rpm Apply 5-15 coats of grossing syrup.
2. Heavy syrup: This
solution contain color, maintaining the above parameters apply several coats.
3. Regular syrup: The process steps are Turn off the heat, reduce the inlet and
outlet air. apply few coats of regular colored syrup to achieve final
smoothness, size
and color development.
4. Finishing
With the heat and inlet air supply off , reduced
exhaust air and pan speed of 12 rpm apply 3-4 coats of regular colored syrup
rapidly. shut off the exhaust air and apply last coat of regular syrup without colorant.
This will give depth to the color and will enhance the elegance of the coat. stop
the pan while the tablets are damp and swiftly shift to jog the pan for 15-30
minutes, leave the tablets overnight to dry completely.
5. Polishing:
this is the final step, the tablets can be
polished in standard coating pan or canvas line polishing pan. The steps
involved are Pan speed 12 rpm inlet air, outlet air turned off apply 3-4 coats
warm polishing solution (waxes), approximately 300 ml
per application. Apply the subsequent coat when
the solvent is evaporated out. Sometimes powder wax are also applied.
Film Coating
To reduce sugar coating process time and to
reduce the requirement for operator skill, film coating was developed. Film
coating is a technique in which a thin layer/coat of a polymer is deposited
over the tablets/particulate. Depending on the coating polymer the types of
coating are
1.Normal film coating
2.Enteric film coating
3.Aqueous moisture barrier coating (AMB)
On the basis of solvent use the types are
1.Organic Coating
2.Aqueous Coating
Materials used in film coating
A typical film coating formulation is made up of
1. Polymer (film former)
2. Plasticizer
3. Colouring/opacifying agent
4. Solvent
5. Others (surfactants, flavors, sweetening agent, active ingredients
and
preservatives.)
An ideal coating material should have the
following properties;
Solubility in solvent of choice for coating
preparation
Solubility required for the intended use
Capacity to produce an elegant looking product
Stability in the presence of heat, light,
moisture, air and substrate being
coated
Odorless, colorless and tasteless
compatibility with other ingredients
Non toxic or no pharmacologic activity
Ease of application
Resistant to cracking
No bridging or filling formation
Ease of printing on high speed machines
Polymers/Film formers
The function of the polymer is to provide main
structure and basic physical
and chemical properties to the coating.
Polymer viscosity is very important specially in
aqueous coating we need to minimize the water concentration, it is to shorten
the process time and to minimize product exposure to the moisture (moisture
sensitive product). But the coating composition with viscosity above 500 cps
are difficult to atomize and will not produce smooth product. Therefore
polymers with low viscosity are preferred.
Nonenteric polymers
The commonly used polymers are
1. Hydroxypropyl methylcellulose (HPMC)
Commercially it is available in different
viscosity grades This polymer is
widely used in air suspension and pan spray
coating. The properties are
1. Soluble in GI fluid, organic and aqueous solvent system
2. Noninterference with tablet disintegration and drug availability
3. Flexibility
4. Chip resistant
5. No odor or taste
6. Stability in presence of light, heat, air and reasonable amount of
moisture
7. Incorporation of colour and other additives with out difficulty
If it is used alone then it may results in
bridging and filling, so it may be used
in combination or proper plasticizer may be
used.
2. Methyl hydroxyethylcellulose
This polymer has also different viscosity
grades, it has similar properties as
that of HPMC but it is soluble in few organic
solvents, which has restricted
its use.
3. Ethylcellulose
Depending on the ethoxy substitution different
viscosity grades are available
commercially. This material is water and GI
fluid insoluble, therefore can not
be used alone for coating. It is used in
combination with water soluble
polymer e.g. HPMC. These combination are a used
for sustained release
coating. The properties include
1. Soluble in wide variety of organic solvents
2. Non toxic
3. Tasteless, odorless and colorless
4. stable at environmental conditions
Unplasticized ethyl cellulose coats are brittle.
4. Hydroxypropylcellulose
1.It is soluble in water below 40oC, GI fluid and organic solvents
2. it is very tacky and yield very flexible film, it can not be used
alone
3. it is good for sub coat but not for color or gloss coat
5. Povidone (PVP)
1.It is available in four viscosity grades i.e. K-15, K-30, K-60 and
K-90, the
average molecular weights are 10,000, 40,000,
160,000 and 360,000
respectively.
2.It is soluble in water, GI fluid and variety of organic solvents.
3. Povidone films are clear, hard and glossy
4. Povidone is soluble in both acidic and intestinal media, it can be
cross
linked with other materials to produce enteric
coating material.
5. povidone is used in coating composition to increase the dispersion
of
color.
3. Sodium Carboxymethylcellulose
1. It is available in low, medium ,high and extra high viscosity
grades
2. It can easily be dispersed in water to form colloidal solution,
but is
insoluble in most organic solvents.
3. the film formed is brittle but adheres well to tablets.
7. Acrylate polymers
Acrylate polymers are marketed under the
trademark of Eudragrit.
Eudragrit E(dimethylaminoethyl methacrylate and
other neutral
methacrylic acid esters) is the only polymer of
this group which is freely
soluble in gastric fluid (acidic media).
8. Polyethylene Glycols
Enteric Polymers
Enteric coating polymers are those substances
which resists the gastric pH
(acidic) and get dissolves in intestinal fluid
(alkaline). The reasons for enteric
coating are
To protect acid labile drugs from gastric fluid e.g. enzymes and
certain
antibiotics
To prevent gastric distress or nausea e.g. sodium salicylate
To deliver drug to intestine for local action
To deliver drugs that are optimally absorbed in the small
intestine
To provide a delayed release component for repeat action tablets.
An ideal enteric coating polymer should have the
following properties
1. Resistance to gastric fluids (acidic pH)
2. Ready susceptibility to or permeability to intestinal fluid
(alkaline pH)
Compatibility with other ingredients
Non toxic or no pharmacologic activity
Ease of application
Formation of continuous film
stability alone and in coating solution. The film should not
change with
aging
Ease of printing on high speed machines
1. Cellulose Acetate Phthalate (CAP)
CAP is widely used but it has major disadvantage
that it dissolves above
pH 6, thus delaying the drug release as the
ideal material may dissolve
around pH 5.
It is also hygroscopic and relatively permeable
to gastric fluid. The film
formed is brittle thus required plasticizer. It
is available under the trademark
of Aquateric from FMC corporation.
2. Acrylate polymers.
Two commercially available acrylates are
Eudragrit L (soluble at pH 6), Eudragrit S (soluble at pH 7)
3. HPMC Phthalate
Three grades are available
HPMCP 55 (HP 50), HPMCP 50 (HP 55) and HPMCP 55S (HP 55S)
These polymers dissolves at lower pH (at 5-5.5)
than CAP and acrylates.
Thus resulting in higher bioavailability of some
specific drugs.
4. Polyvinyl Acetate Phthalate (PVAP)
It is similar to HP 55 in stability and pH dependant solubility.
Plasticizer
The function of plasticizer is to modify the
basic mechanical properties of
the polymer. Plasticizers have high affinity for
the polymer they are also
called nonvolatile solvents.
There are two techniques to modify the
plasticity of the film former;
1.Internal plasticizing
2.External plasticizing
In the former technique chemical modification is
brought in the polymer
which alters the physical properties of the
polymer i.e. elastic modulus. In
later technique other substances are used as
plasticizer in the formulation.
When the plasticizer is used in correct
concentration it imparts flexibility by
relieving the molecular rigidity. Commonly 10%
of polymer concentration is
used. Examples include
1.Castor Oil
2.PEG 200 and 400
3.Propylene glycol
4.Glycerin
5.Polysorbates (tweens)
6.Sorbitan esters (spans)
Coloring and opacifying agent
The function of these ingredients is to enhance
the product quality. They
provide
1.Product identification
2.Protect the core from light and moisture
3.They increase the solid concentration with any impact on viscosity
thus
reducing the drying time. They are either
soluble or form fine suspension
in the solvent system. For uniform distribution
the particle size must be
10 microns. The most common colorants used are
FD&C or D&C
certified, these are either dyes or lakes of
dyes. Examples include iron
oxide, anthrocyanins, caramel, carotenoids,
chlorophyll, indigo, flavones,
turmeric acid and carminic acid.
Opacifiers are used to give more pastel color
and increase film coverage.
These can provide white coat or mask the color
of the tablet core. These
are mostly inorganic material. The substances
employed are
1.Titanium dioxide (Most Common)
2.Talc
3.Aluminum silicate
4.Magnesium carbonate
5.Calcium sulfate
6. Aluminum hydroxide
Solvents
The function of the solvent is to dissolve or
disperse the polymers and other
additives and transfer them to the surface of
substrate (core) the ideal
characteristics are
1.It should either dissolve or disperse the polymer system and other
ingredients.
2.Small concentration of polymer (2-10%) should not high viscous
solution
3.It should be colorless, tasteless, odorless, inexpensive, inert
and noninflammable.
4.Should have rapid drying rate
5.Should not have environmental impact.
The most widely solvents used either alone are
in combination are water, ethanol,
methanol, isopropyl alcohol, chloroform ,
acetone , methyl ethyl ketone and
methylene chloride.
Problems
and remedies for tablet coating:
Blistering
Definition: It is
local detachment of film from the substrate forming blister.
Reason: Entrapment of
gases in or underneath the film due to overheating either
during spraying or at the end of the coating run.
CAUSE:
Effect of temperature on the strength,
elasticity and adhesion of the film.
REMEDY:
Use mild drying
condition.
Chipping:
Definition: It is
defect where the film becomes chipped and dented, usually at the
edges of the tablet.
Reason: Decrease in
fluidizing air or speed of rotation of the drum in pan coating.
CAUSE
High degree of attrition
associated with the coating
process.
REMEDY:
Increase hardness of the film by
increasing the molecular weight grade
of polymer.
Cratering
Definition: It is
defect of film coating whereby volcanic-like craters appears
exposing the tablet surface.
Reason: The coating solution
penetrates the surface of the tablet, often at the
crown where the surface is more porous, causing localized
disintegration of the
core and disruption of the coating.
CAUSES:
1.Inefficient drying.
2.Higher rate of
application of coating
solution.
REMEDIES:
1. Use efficient and optimum drying
conditions.
2.Increase viscosity of coating
solution to
decrease spray application rate.
Sticking
and Picking
Definition: It is defect where isolated areas of film are pulled away
from the surface
when the tablet sticks together or to
the coating pan and then detached from one
another
or from the pan and piece of film get remained to the pan or the other tablet
exposing
the core.
Reason:
Conditions similar to cratering that
produces an overly wet tablet bed where
adjacent tablets can stick together and
then break apart.
CAUSE:
1.Inefficient drying.
2 . Higher rate
of application of coating solution.
REMEDY:
1.Use optimum
and efficient drying conditions or
increase the inlet air temperature.
2.Decrease the
rate of application of coating solution by
increasing viscosity of coating solution.
Pitting
Definition: It is
defect whereby pits occur in the surface of a tablet core without any
visible disruption of the film coating.
Reason: Temperature of the
tablet core is greater than the melting point of the
materials used in the tablet formulation.
CAUSE: REMEDY
1.Inappropriate
drying (inlet air )
temperature
REMEDY
Dispensing with preheating procedures at the
initiation of coating and modifying the drying (inlet
air) temperature such that the temperature of the tablet
core is not greater than the melting point of the batch
of additives used.
Blooming/Hazing/Dull Film
Definition: It is
defect where coating becomes dull immediately or after prolonged
storage at high temperatures.
Reason: It is
due to collection on the surface of low molecular weight ingredients
included in the coating formulation. In most circumstances
the ingredient will be
plasticizer.
CAUSE REMEDY:
1.High concentration and low
molecular weight of
plasticizer.
2.High processing temperature,
especially when using
cellulosic polymer
REMEDY:
1.Decrease plasticizer concentration and
increase molecular weight of
plasticizer.
2.cellulosic polymer
Appropriate drying temperature
Blushing
Definition: It is
defect best described as whitish specks or haziness in the film.
Reason: It is
thought to be due to precipitated polymer exacerbated by the use of
high coating temperature at or above the thermal gelation
temperature of the
polymers.
CAUSES:
1. High coating temperature
2. Use of sorbitol in formulation which
causes largest fall in the thermal
gelation temperature of the Hydroxy
Propyl Cellulose, Hydroxy Propyl
Methyl Cellulose, Methyl Cellulose
and Cellulose ethers.
REMEDIES:
Avoid use of sorbitol with Hydroxy
Propyl Cellulose, Hydroxy Propyl
Methyl Cellulose, Methyl Cellulose
and Cellulose ethers.
Orange peel/Roughness
Definition: It is
surface defect resulting in the film being rough and nonglossy.
Appearance is similar to that of an orange.
Reason: Inadequate
spreading of the coating solution before drying.
CAUSES
1. Rapid Drying
2. High solution viscosity
3.Indiscriminate use of superdisintegrant
Correct quantity, decrease flow rate.
REMEDIES
1.Use mild drying conditions
2.Use additional solvents to decrease
viscosity of solution.
3.Correct quantity, decrease flow rate
Cracking/Splitting
Definition: It is
defect in which the film either cracks across the crown of the tablet
(cracking) or splits around the edges of the tablet
(Splitting)
Reason: Internal stress in
the film exceeds tensile strength of the film.
Colour variation
Definition:A
defect which involves variation in colour of the film.
Reason: Alteration
of the frequency and duration of appearance of tablets in the
spray zone or the size/shape of the spray zone.
Bridging and Filling
Definition: Bridging
is defect in which the bisects or monogram is obscured. During
drying the film may shrinks and pull away from the corners
of intagliation or bisects.
In filling the bisects or monogram is filled with coating
solution.