Process of coating
Types of coating
Mechanism of coating
Factors affecting the process
USP standards & specifications
Principle of Plasticization
Role of polymer
Polymers used for conventional coating
Polymers used for Enteric coating
Commercially available coating systems
Process of Coating
Application of thin polymeric film over
the core surface( tablet, pellets,
granules & dosage units ) to form a
smooth surface with uniform distribution
optimizing the quality of product with
-Functional point of views.
Advantages of Coating
Improves aesthetic qualities of product
Masking of unpleasant taste & odor
Improving patient compliance
Increased product stability
Modifying drug release behavior
Events During Film formation
Initial rapid evaporation of solvent from
the atomized droplets of coating liquid
causing: a) increase in polymer
concentration (viscosity) b)reduction in
volume of droplets
Further loss of solvent from the film at a
slower rate (diffusion controlled)
Immobilization of polymer molecules at
solidification point (tablet surface)
Further gradual loss of solvent at a
much reduced rate
Factors affecting the process
Factors has influence on (parameter)
Ingredients Wetting of coating liquid
Porosity Dry film adhesion
Surface roughness Spreading of coating solution
2. Coating liquid
Solids content Coating liquid viscosity
Viscosity of solution Spreading and coalescence
Surface tension Wetting, spreading & coalescence
3. Process of drying
Drying rate Viscosity of coating liquid &Structure of dried
Heat applied Development of internal stress & Mechanical
USP Standards & Specifications
Enteric coated tablets must tolerate agitation in
simulated gastric fluid test solution at 37± 2 ◦ c (no
discs). After 1 hour of exposure in simulated gastric
fluid, tablets must present no evidence of
disintegration, cracking or softening.
Then a disc is added to each tube, and the test is
continued using simulated intestinal fluid
maintained at the same temperature as mentioned
above. The test is conducted for 2 hours to the time
specified in the individual monograph.
The batch passes the test if all tablets disintegrate.
If 1 or 2 tablets fail to disintegrate completely, the
test is repeated on 12 additional tablets. At the end
at least 16 out of 18 tablets should disintegrate
within the specified time in order to pass the test.
Polymers used for pharmaceutical dosage
forms for coating are generally amorphous in
Unfortunately Glass transition temperature of
most of the polymers are in excess of
conditions exposed for the pharmaceutical
manufacturing. Thus one needs to incorporate
plasticizer basically for two main reasons:-
Modification of polymer properties so as to
impart flexibility which reduces the Tg of
To facilitate the processing of dosage form at
substantial temperature conditions to protect
the integrity of active ingredient.
Polymers for conventional
Acrylics Co-polymers such as methyl
methacrylate, ethyl methacrylate
Hydroxy propyl methyl
Material of choice for air suspension and
pan spray coating.
High moisture stability, photo-stability and
Flexibility, tasteless and odorless.
Compatible with additives with additives
Solubility characteristic of the polymer in
Ethyl cellulose (EC)
Various viscosity grades are available.
degree of Ethoxy substitution.
o Completely insoluble in water and G.I.
o Soluble in wide variety of organic solvents
o Non-toxic odorless and tasteless.
o Requires plasticizers.
o Pseudo latex systems using aqueous
polymeric dispersions can be formed using
ethyl cellulose having low viscosity and
high solid content
Sodium Carboxy Methyl
Available in low, medium, high and extra
high viscosity grades.
Easily dispersed in water to form
Not a material of choice for coating
based on organic solvents as it is
insoluble in most organic solvents.
Preferably used for aqueous film coating
solutions with high coating efficiency
Polyethylene Glycol (PEG)
PEG is available in grade ranging from
PEG has low contact angle –penetration into
powder bed and make contact with substrate
Desirable melting range Molecular weight.
Waxy and hygroscopic, soften readily at
moderately elevated temperatures.
Low molecular weight PEG’s are used as
plasticizers in coating solutions rather than as
Acrylate polymers are generally
marketed as Eudragits.
Eudragit RL and RS are copolymers
synthesized from methacrylic acid esters
with low content of quaternary
Enteric Coating Polymers
Cellulose Acetate Phthalate Susceptible to Hydrolysis
Cellulose Acetate Trimellitate Susceptible to Hydrolysis
Polyvinyl Acetate Phthalate Susceptible to Hydrolysis
HPMC-Phthalate Susceptible to Hydrolysis
HPMC-Acetate Succinate Susceptible to Hydrolysis
Poly (MA -EA) 1 : 1 ------
Poly (MA -MMA) 1 : 1 High Dissolution pH
Poly (MA -MMA) 1 : 2 High Dissolution pH
Cellulose Acetate Phthalate
Relatively hygroscopic and permeable to
gastric fluids and moisture.
Films formed from CAP are brittle.
Usually formulated with hydrophobic
excipients to achieve a better enteric film.
Colloidal dispersion of latex particles
comprising of polymeric spheres of CAP
(aquateric) have been developed and
Dissolves only above pH 6 and delays the
absorption of drugs
Dissolves at a relatively lower pH (5-5.5)
than CAP or acrylic copolymers.
This Solubility characteristic may result
in higher bioavailability of certain drugs.
Different grades are available
Stability is higher compared to CAP
Absence of labile acetyl groups
enteric coating systems
Product Polymer Form Characteristic
Eudragit L30D Poly (MA-EA) 1:1 Latex Dispersion Essentially
Eudragit L 10055 Poly (MA-EA) 1:1 Spray Dried latex Dispersed in water
Coateric PVAP Dry powder Dispersed in water
Aquateric CAP Spray dried Dispersed in water
CAP CAP Dry powder Dissolved in water
CAT CAT Dry powder Dissolved in water
HPMC-P HPMC Dry powder Dispersed in water
Eudragits Availability applications Dissolution properties
Eudragit L Powder Drug delivery in > 5.5
Eudragit D Aqueous Drug delivery >5.5
100-55 dispersion 30% duodenum
Eudragit L 100 Powder Drug delivery in >6.0
Eudragit S 100 Powder Drug delivery in >7.0
Eudragit FS 30 Aqueous drug delivery in >7.0
D Dispersion 30% colons.
The EUDRAGIT grades for enteric coatings are based
on anionic polymers of methacrylic acid and
methacrylates. They contain –COOH as a functional
group. They dissolve at ranges from pH 5.5 to pH 7.
Application benefits of enteric EUDRAGIT coatings:
PH-dependent drug release
Protection of actives sensitive to gastric fluid
Protection of gastric mucosa from aggressive actives
Increase in drug effectiveness
Good storage stability
GI and colon targeting
Use of Hot melt extrusion in
Enteric coating of tablets
“The manufacture and characterization of hot-melt
extruded enteric tablets”
Eudragit L100-55, an enteric polymer, was pre-
plasticized with triethyl citrate (TEC) and citric acid and
subsequently dry-mixed with 5-aminosalicylic acid, a
model active pharmaceutical ingredient (API).
Powder blends were hot-melt extruded as cylinders,
cut into tablets.
The authors concluded that Increasing the
concentration of TEC significantly lowered the glass
transition temperature (Tg) of Eudragit L100-55 and
reduced temperatures necessary for extrusion as well
as the die pressure.
Influence of method of manufacture on the release of 5-ASA from Eudragit
L100-55 tablets in 0.1 N HCl dissolution media (pH 1.2). () HME tablet; (■)
compressed tablet with hardness value of 62 ± 2 N; (○) compressed tablet
with hardness value of 230 N ± 12 N.
This leads to suggest that hot melt
extrusion, a versatile process can be
utilized to decrease the compression
pressure in order to optimize formulation
parameters affecting compressional
behavior of materials such as MCC that
in conventional enteric coating
techniques employ high compressional
Case study 2
Controlled release of dual drug-loaded
hydroxypropyl methylcellulose matrix tablet
using drug-containing polymeric coatings. By
Beom-Jin Lee, , Seung-Goo Ryu and Jing-Hao
Dual drug loaded HPMC matrix tablet that
conatins drug in inner tablet core and outer
Aqueous based Eudragit RS 30 D dispersionis
The dual drug-loaded HPMC matrix tablet
gave a biphasic linear release, showing a
zero-order for 4 h (first) followed by another
The current dual drug-loaded HPMC matrix
tablet, showing biphasic release profiles may
provide an alternative to deliver drugs with
circadian rhythmic behaviors in the body.
The dual drug-loaded coating method is also
interesting for the modified release of poorly
water-soluble drugs because solubilizers and
other additives can be added in drug-
containing polymeric coating dispersions.
Coating can be dated as back as in
ancient times when an experienced
individual would dip a bitter tablet into
Since then the process of coating has
been constantly an area of interest for
oral dosage forms.
With the emergence of newer polymers
that are pH dependent, acid resistant
and many other properties.
Utilization of dual coating in case of
polymers such as HPMC may result into
development of newer techniques in
case of coating.
Thus it can be concluded that coating
has been, is and shall continue to be
one of the most promising area in
formulation of oral dosage forms for
improved health care.
“If we knew what we were doing, it
would not be called research”