coating Flashcards
what is coating
It is the application of a coating material to the exterior of a
tablet with the intention of achieving benefits and properties
to the dosage form over the uncoated ones.
why do we use coating
- Extend shelf life by protection of the ingredients from the
environment (light, moisture and oxidation). - Coating provides an efficient sealing of the tablet cores as a
method of taste masking for drugs that have bitter or
unpleasant taste, or unpleasant odor. - Tablets that are coated are somewhat easier to swallow than
uncoated tablets (significant for large tablets). - Coloured coatings mask any batch differences in the
appearance of raw materials (patient concern). - Coloured coatings aid in the rapid identification of product
by the manufacturer, dispensing pharmacist and patient. - Coating tablets facilitates their handling on high speed
automatic filling and packaging equipment (as a result of
improved product flow and mechanical strength). - Cross contamination is also reduced in the manufacturing
plant, as ‘dusting’ from tablets is eliminated by coating. - Functional film coatings are used to impart modified release
properties to the coated tablet. - Coatings may be optimized with respect to colouration and
gloss to aid in their sales appeal. - Avoid chemical incompatibilities by incorporating another
drug in the coa
what are the types of coating
- Film coating
- Sugar coating
- Compression coating
what is film coating
Film coating is the more contemporary and thus commonly
used process for coating oral solid dosage forms.
First introduced to the pharmaceutical industry in the 1950’s
Nowadays all newly launched coated products are film
coated rather than sugar coated
what are the different types of film coating
- Immediate release film coating (also known as non-functional
coating): the coating has no measurable effect of
biopharmaceutical properties. This coating is readily soluble in
water. Thus, the coating is mainly used to provide improved
appearance, taste-making and/or identification to the tablets. - Modified release film coating (also known as functional
coating): maybe further categorized as either delayed release
(e.g. enteric or gastro-resistant coating) or extended release
coating (i.e. sustained, prolonged, controlled release coating).
what is gastro-resistant coating (delayed release )
are only soluble in water at pH values
grated than 5-6. Therefore they are either used:
1. to protect the drug while the tablet is in the stomach, in the
case of acid labile drugs
2. Or to prevent drug release in the stomach, in the case of drug
that are gastric irritant
what is extended release coating
are mainly insoluble in water. They are
designed to ensure that the drug is release over a relatively long
period time (typically 6-12 hours). Extended release formulations
reduce the number of doses a patient needs to take throughout
the day and often improve drug efficacy
what is film coating
a process in which polymer –
based coatings are applied on the surface of drug-containing
dosage units (either tablets, pellets, granules, capsules or drug
powders and crystals).
Such coating is thin (in the range of 20 - 200μm).
The dosage unit on which the coating is applied is defined
core.
The coating liquid (solution or suspension) contains a polymer in
a suitable liquid medium in addition to pigments and plasticizers.
1. This liquid is sprayed (i.e. atomized) on to a rotating, mixed
tablet bed or fluid bed.
2. The drying conditions permit the removal of the solvents so as
to leave a thin deposition of coating material around each
tablet core.
what are the basic requirements for any film coating equipment
- Adequate atomization (conversion into very fine droplets) of
the spray liquid for application to the tablet cores. - Adequate mixing and agitation of the tablet bed. Spray
coating relies upon each tablet passing through the area of
spraying. - Sufficient energy input in the form of heated air to evaporate
the solvent. - Good exhaust facilities to remove dust and air carrying the
evaporated solvents
what are the two different film coating equipment
- Side-vented coating pans
- Fluid bed
what is the side vented coating pan
Also called perforated coated pan. These equipments consist of
perforated or partially perforated drums that are rotated on their
horizontal axis.
Baffles are often placed in the coating pans to facilitate tablets
tumbling within the pan for a more uniform film distribution.
Some designs include: Accela Cota, Glatt coater, Driacoater.
what is unique about accela cota side vented coating pan
Air is directed into the drum, is passed through the tablet bed and
is exhausted through the perforations in the drum
what is unique about glatt side vented coating pan
Similar technology to the
Accella Cota
Here, the horizontal process air
flow minimises turbulence in the
spray nozzle area and therefore
contributes to improved
coating result
what is unique about driacoater side vented coating pan
It introduces drying air through hollow
perforated ribs located on the inside
periphery of the drum. The ribs dip
into the bed as the pan rotates.
Drying-air passes through the tablet
bed.
Exhaust is from the back of the pan.
what is the fluid bed dryer
Fluidized bed coaters function by suspending a bed or a
column of solid particles in a moving gas stream.
A fluidized bed occurs when a quantity of solid particles are
placed under appropriate conditions to cause the mixture to
behave as a fluid. This is typically done by forcing pressurized
air, through the bed of solid particles. This causes the solid
particles (e.g. powders or tablets) to acquire properties and
attributes similar to those of normal fluids, resulting in what is
known as fluidization.
what is the fluid bed dryer
Fluidized bed coaters function by suspending a bed or a
column of solid particles in a moving gas stream.
A fluidized bed occurs when a quantity of solid particles are
placed under appropriate conditions to cause the mixture to
behave as a fluid. This is typically done by forcing pressurized
air, through the bed of solid particles. This causes the solid
particles (e.g. powders or tablets) to acquire properties and
attributes similar to those of normal fluids, resulting in what is
known as fluidization.
what are the different patterns for fluid bed dryers
Top spray.
Bottom spray.
Tangential spray
what is top spray
The spraying nozzle is located on top of the
product chamber. The liquid is sprayed in the
opposite direction to material motion.
If the spray formulation contains a volatile
solvent, evaporation of this solvent from the
spray droplets occur.
The top-spray coating method is particularly
recommended for taste masking on particles
(less used for tablets).
what is bottom spray
Also called Wurster process.
The material (e.g. tablets) to be coated are fed into a
vertical column (Wurster column).
The air that enters from the bottom of the column. The
tablets move upwards and rotate.
As the coating solution enters the system from the bottom,
it is rapidly applied to the suspended, rotating solids with
rounding coats being applied in less than an hour.
The airflow is controlled so that more air enters the center
of the column. The movement of the tablets is upward
through the center of the chamber. They then fall toward
the chamber wall and move downward to re-enter the air
stream at the bottom of the chamber.
Bottom-spray method is recommended for sustained-release
and enteric-release products (for tablets and pellets).
The most commonly known fluid-bed process for coating in the
pharmaceutical industry.
what is tangential spray
The spray nozzle is located on the side of the
product bed. Liquid is sprayed in a tangential
pattern while the materials are in motion.
Here, the bottom plate is not perforated (as in
other fluid bed designs). The bottom disk rotates.
A gap is present between the chamber wall and
the rotating disk. Air flows from the bottom
through this gap.
The disk motion together with that introduced by
the fluidizing air and the gravitational force
cause the materials to move in rope-like motion.
The tangential method is mainly used for sustained-release
and enteric coated products (for pellets).
The high kinetic energy in this equipment is generally
destructive for larger and non-spherical products (i.e. tablets).
what do we add to the tablet when we film coat it
Solvent
Polymer
Plasticizer
Colourants
what do we add to the tablet when we film coat it
Solvent
Polymer
Plasticizer
Colourants
what properties should we consider when we film coat
- Solubility
The functionality of the final coating (e.g. taste masking or modified
release) depends on the solubility of the polymer chosen:
polymers soluble in aqueous fluids (i.e. GI fluids) should be chosen
for non-functional coatings of immediate release products.
polymers with limited or no solubility must be chosen for coating
to provide modified release (i.e. in this case the coating must act
as a barrier to liquid penetration into the tablet). - Mechanical properties
Upon deposition and drying on the surface of the tablet, the
polymer should form a film:
of good strength: in order to resist the mechanical stresses
during coating and tablet handling;
of good flexibility: in order to minimize film cracking during
handling and storage;
of good adhesiveness: in order to ensure that the coating
remains adherent to the surface of the tablets right up to the
point of being taken by the patient.
what polymer should we use for non functional release
Cellulose derivatives (Hydroxypropyl Methylcellulose HPMC,
Hydroxypropylcellulose HPC, Hydroxyethylcellulose HEC,
Methylcellulose MC)
Vinyls (Polyvinyl pyrrolidone, PVP)
Glycols (Polyethylene glycols, PEG’s)
Aminoalkyl methacrylate co-polymers
what makes Aminoalkyl methacrylate co-polymers special
They are readily soluble in aqueous media only at low pH (i.e.
pH 5).
This characteristic makes this polymer excellent for tastemasking purposes:
• Coating insoluble in saliva
• Coating rapidly soluble in the stomach
what polymer do we use in enteric coating
The most commonly used include:
Polymers derived from Cellulose (Cellulose Acetate Phthalate CAP,
Hydroxypropyl Methylcellulose Phthalate HPCMP);
Methacrylic acid co-polymers;
Polyvinyl Acetate Phthalate, PVAP.
All of these polymers are insoluble in aqueous media at acidic
pH, but soluble at pH > 5-7.
what polymers should we use in extended release
Polymers used in extended release film coating include
Cellulosic polymers (Ethylcellulose);
Acrylic esters;
Polyvinyl acetate.
Most polymers used for such coating are insoluble in water at
any pH.
how do we choose the solvent
Non-functional coatings (generally water-soluble) are normally
applied as a water-based coating solutions of the polymer.
Functional coating (with limited or no solubility in water) were
traditionally applied as organic coating solutions of the polyme
what are the problems for organic solvents
- Environmental issues - the release of untreated organic solvent
vapour in the atmosphere is ecologically unacceptable - Safety issues – organic solvents are flammable and explosive
hazard; moreover they expose the operators to toxic hazards - Financial issues - relatively expensive solvents. Moreover, costly
explosion-proof processing areas and equipment are
necessary. - Solvent residue issues – after drying of the coating, residues of
the solvent inevitably remain in the film. Strict regulations require
to quantify and limit the residue leve
how do we avoid using organic solvents
As a means to avoid organic solutions of the polymer for waterinsoluble polymers, scientists developed aqueous pseudolatex
colloidal polymer dispersions:
These dispersions for film-coating contain very small (i.e.
colloidal) polymer particles (≈ 100 nm in size) dispersed in
aqueous media.
When these polymer dispersions are applied on tablets for
coating, film of good quality can be formed
Aqueous pseudolatex colloidal polymer dispersions are
nowadays extensively used in the pharmaceutical industry.
However, several researches showed better film characteristics
and functionality when the polymer is formed from solutions of
polymers, rather than dispersions
what are plasticizers and why do we use them
They are excipients added to the film-coating solution or dispersion
to modify the physical properties of the polymer:
Most polymers are brittle or hard in nature, therefore they
cannot form film of the required physical characteristics.
Inclusion of plasticizers in the coating formula has the following
benefits:
Increased film flexibility and plasticity
Reduce stress within the coating → reducing the tendency of
the coating from shrinking or pull away from corne
how do plasticizers work
The molecules of the plasticizer interpose themselves between
the polymer molecules. → This increase the free-volume between
polymer chains and facilitating the polymer chains motion within
the structure of the coating.
give examples on some plasticizers
Water soluble: Glycerin, propylene glycol, low molecular
weight polyethylene glycols (PEG 200 and 400), Triethyl citrate.
Water insoluble: Dibutyl phthalate (DBP), Diethyl phthalate
(DEP), Tributyl citrate (TBC).
For plasticizers to function properly:
they should be soluble in the solvent of the coating formulation
They should be in intimate contact with the polymer
molecules: hydrophilic in case hydrophilic polymers -
hydrophobic in case hydrophobic polymers
give examples on some plasticizers
Water soluble: Glycerin, propylene glycol, low molecular
weight polyethylene glycols (PEG 200 and 400), Triethyl citrate.
Water insoluble: Dibutyl phthalate (DBP), Diethyl phthalate
(DEP), Tributyl citrate (TBC).
For plasticizers to function properly:
they should be soluble in the solvent of the coating formulation
They should be in intimate contact with the polymer
molecules: hydrophilic in case hydrophilic polymers -
hydrophobic in case hydrophobic polymers
what are colourants
colourants Usually water-insoluble colours (pigments).
Pigments have certain advantages over water-soluble colours
(dyes): they are more chemically stable towards light1, provide
better opacity and covering power2, optimize the impermeability
of a given film to water vapour3, and less migration during drying4.
Examples of colourants:
Iron oxide pigments.
Titanium dioxide.
Aluminium Lakes (pigment manufactured by precipitating a dye with an
inert binder)
what types of defects film coating might have
- Visual defects
- Defects that affect functional properties
what are the visual defects that might happen
- Processing issues
These are issues related with the coating process itself.
They generally are related to an imbalance between the rate of
spraying of the coating liquid and the rate of evaporation during
the drying process. The imbalance result in either in:
Overwetting (resulting in “sticking” of tablets)
Overdrying (resulting in inadequate spreading of the coating
solution and causing a bumpy “orange-peel” effect on the
coating – moreover overdrying sometimes results in
detachment of the film from the core, i.e. “blistering”) - Formulation issues
These are issues related with some deficiency in the core or
coating formulation.
Core formulation issues are often related to insufficient
mechanical strength of the tablets, leading to tablets
breakage or erosion.
Coating formulation issues often result in a film of inadequate
mechanical strength: leading to film “cracking”, uneven
coating in the logo (“bridging”) or “peeling” of the coating.
Such problems may be minimized with an appropriate choice
of the plasticizer type and concentration in the formulatio
what is sugar coating
The traditional method of coating tablets.
It involves the successive application of sucrose-based
solutions to tablet cores in suitable coating equipment.
Conventional panning equipment with manual application of
syrup has been extensively used in the past.
More specialized equipment and automated methods are
now making an impact on the sugar coating process.
what is sugar coating
Sugar coating is a process during which aqueous formulations
(i.e. syrup) are literally poured directly onto the tumbling tablets.
The traditional method of coating tablets.
It involves the successive application of sucrose-based
solutions to tablet cores in suitable coating equipment.
Conventional panning equipment with manual application of
syrup has been extensively used in the past.
More specialized equipment and automated methods are
now making an impact on the sugar coating process.
what is the process involved in sugar coating
- Sealing of tablet cores
- Subcoating
- Smoothing
- Colouring
- Polishing
- Printing
how do we stop water from reaching the core and ruining the tablet
To prevent these problems, the
cores are usually sealed initially with a water-proof, sealing coat.
Tablet sealants are generally water-insoluble polymers applied
from an organic solvent solution. Examples of tablets sealants:
Shellac
Cellulose acetate phthalate.
Polyvinyl acetate phthalate.
when the sugar coating is used for immediaterelease purposes, the amount of seal coat applied should be
minimal. An excessively thick seal coat (made of water-insoluble
polymers) would in fact slow down tablet disintegration and
dissolution.
what is sub coating
Sugar coated tablets have a completely smooth profile with no visible
edges remaining from the original tablet core. For this reason, sugar
coating are applied in large quantity to the tablet core (increasing
the weight by 50-100%).
Most of the material build-up occurs during the subcoating stage:
subcoating is applied to build up the tablet size and round the edges
The process of subcoating is usually performed by adding bulking
agents such as calcium carbonate or talc to the applied sucrose
solutions. Talc also act as anti-adherent.
A gum such as acacia is also added as a binder to increase
adhesion of calcium carbonate and talc to the coat and to
reduce brittleness
how can we accomplish subcoating
- The application of a gum/sucrose solution followed by
dusting with powder (calcium carbonate and/or talc) and
then drying. This routine is repeated many times until the
desired shape is achieved. - The application of a suspension of dry powder (calcium
carbonate and/or talc) in the gum/sucrose solution
followed by drying. As above the procedure is repeatedly
performed until the correct shape is achieved
what is smoothing
After the correct profile has been attained, the subcoated
tablets will have a rather rough surface.
The purpose of the smoothing step is to cover and fill in the
imperfections in the tablet surface caused by subcoating. The
achievement of a smooth surface is essential to facilitate the
application of the colouring layer
They are made smooth by successive applications of dilute
syrup. Tablets are subjected to drying air after each application
what is smoothing
After the correct profile has been attained, the subcoated
tablets will have a rather rough surface.
The purpose of the smoothing step is to cover and fill in the
imperfections in the tablet surface caused by subcoating. The
achievement of a smooth surface is essential to facilitate the
application of the colouring layer
They are made smooth by successive applications of dilute
syrup. Tablets are subjected to drying air after each application
what is the color coat made from
Water soluble dyes
Water insoluble pigments
what is polishing
To achieve a glossy finish (typical of sugar-coated products) a
final stage involving the application of waxes is employed: the
tablets receive one or two applications of a wax dissolved in an
organic solvent. Usually beeswax or carnauba wax is used.
what are the Ideal characteristics of sugar-coated tablets
Sugar-coated tablets should ideally be of a perfectly smooth
rounded contour with even colour coverage.
They are usually polished to a high gloss.
Any printing should be distinct, with no smudging or broken print.
what equipment do we use for sugar coating
a traditional rotating
sugar-coating pan:
A circular metal pan mounted angularly on a stand. The pan
is rotated on its horizontal axis by a motor.
A supply of drying air (preferably of variable temperature
and thermostatically controlled).
An extraction to remove dust and moisture laden (enriched)
air.
The coating liquid was traditionally manually poured on to
the rotating tablets
or Perforated pan systems (side-vented) described in the filmcoating sections have been more recently used: these enable
to better control the coating process and to speed it up.
what is compression coating
- The tablet core is first prepared by compression.
- Then the tablet is mechanical transfer on a slightly
larger die, that was previously pre-filled with a portion
of the coating granules. The tablet core is position
centrally into this partially filled die. - More coating granules are filled on the top of the core.
- The whole composition undergoes a second
compression process.
The granules used to form the coating should not be
neither large or irregularly shaped as this will cause the
core to tilt during the second compression, leading to the
formation of an uneven coating.
Press coating is often used in the separation of chemically
incompatible materials in tablets (combination tablets).
It is even possible to apply two press coatings where an inert
(placebo) middle layer separates the active core from the
coating.
The press coating also offers potential for having a dual
release pattern.
The use of the process is limited by the relative complexity of
the mechanism used in the compression equipment
