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Anika Tabassum Bristy
North South University
Tablet coating :
Tablet coating is defined as “ covering the
tablets with one or more layers of mixture of
various substances such as natural or
synthetic resins ,gums ,inactive and insoluble
filler, sugar, plasticizer, polyhydric alcohol
,waxes , authorized color and some times
Aspects of tablet coating :
Avoid irritation of stomach
Avoid bad taste
Avoid inactivation of drug in the stomach
Improve drug effectiveness
Reduce influence of moisture
Improve drug stability
Improve product identity
Improve appearance and acceptability
Coating defects :
An ideal coated tablet should be free
from any visual defect or functional
defect. But some imperfections are
seen in the tablet coating for different
kinds of reasons .
The imperfections found in tablets
coating are known as tablet coating
Some coating defects •
tablets stick together.
Most common in capsule
shaped tablets .
Coating suspension can not be evaporated.
Reducing spray rate
Increasing pan speed
Small, fine cracks observed on the
upper and lower central surface of
tablets, or very rarely on the
sidewall are referred to as ‘Cracks’.
• Use of higher
polymers or polymeric
• Higher internal stresses
in the film ( more than
tensile strength of the
• Use low molecular weight polymer
• Adjust the plasticizer & pigment types and
concentration to minimize internal stresses
Sticking & picking
is defect where isolated areas of
film are pulled away from the
surface when the tablet sticks
together and then part.
Picking does not occur alone it must
have another tablet to be stuck with
which called sticking .
Sticking & picking
Higher rate of application of
Excessive film thickness
• Reduce liquid
• Increase in drying air
temperature and air
It is local detachment of film from the
substrate forming a blister .
Over heating during
spraying coating solution
Remedy : use mild drying
o It is the defect where film become
chipped and dented , usually at the
edges of tablet .
• Excessive attrition during
Increase hardness of the film .
Orange peel effects
refers to a coating texture that
resembles the surface of an orange .
• Rapid Drying
• High solution viscosity
• Use mild drying conditions
• Use additional solvents to
decrease viscosity of solution.
The surface becomes
rough and no glossy .
Reduce the degree of
fills in the letter or logo on
the tablet .
• Improper formulation
• Poor logo design
• Improper application of
• Improper atomization
• High percentage of solid in
• High coating viscosity
• Increase plasticizer contents or change
• Reduce viscosity of coating solution
monogram or bisect is filled
and become narrow .
• Applying too much
• Higher solution applying
Control fluid application rate
Blooming (Hazing/dull film)
Coating becomes dull immediately
or after a prolonged storage .
Normally it occurs together with
using low molecular weight plastisizer .
Remedy plastisizer .
increase MW & concentration of
• Inadequate drying
• Lack of tablet
Remedy – Control drying rate & temparature
It is defect whereby pits occur in the
surface of tablet core
• Incontinuous spreading of film
• temperature of the tablet core is greater than
the melting point of the materials used in tablet
control drying temperature
Two types of color
Individual Tablet Color
• Whole Batch Color
uneven spray pattern,
migration of soluble dyes ,
plasticizer and other
additives during drying.
• Use of lake dyes eliminates dye migration.
• A reformulation with different plasticizer
and additives is the best way to solve film
is the defect of film coating whereby
volcanic-like craters appears exposing
the tablet surface .
• Penetration of the coating solution into the
surface of the tablet
• Decrease in spray application rate
• Use of optimum and efficient drying
Blushing (whitish specks)
The defect best described as whitish specks or
haziness of the film .
It is characterized by precipitation of polymer
exacerbated by the use of high coating
temperature at or above the thermal gelation
temperature of the polymers.
Agglomeration caused by coating
suspension cannot be evaporated as
soon as it reach the tablet which may
be caused from too much inlet
coating suspension or too less inlet
heat and the unevaporated
suspension glue the tablets together.
The amount of excess unevaporated
suspension is much more than
Sometimes it can cause by the leaking
of coating suspension into the
chamber, or too close spraying
distance or too low atomizing pressure.
Forms – Tablets
- Larry L. Augsburger, Stephen
Tablet Coating by Air
- Clarence James Endicott