An Extensive review on "Tablet Coating defects"

1. Tablet Coating Defects
Presented by:
 Bhushan Sirsikar
(NIPERA1719PE15)

2. Flow of Seminar
Introduction to tablet coating
Need to coat a tablet
Problems and Remedies for tablet
coating
Critical parameters for successful
coating of tablets

3. Tablet coating
Tablet coating is the application of coating material
to the exterior of a tablet with the intention of
conferring benefits and properties to a dosage form
over the uncoated variety.
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4. Tablet Coating process
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Fig.2. Schematic representation of tablet coating process

5. Why To Coat a tablet..??
 Bitter taste or unpleasant odour.
 Protecting the drug from surroundings (Stability).
 Handling & ease of ingesting by patients.
 Mechanical protection from breakage.
 Light incompatibility
 Environmental Oxidation.
 In-elegant core.
 Modifying the drug release profile.
 Product identity.
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6. PROBLEMS AND REMEDIES FOR TABLET COATING
 BLISTERING
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
Causes Remedies
 Effect of temperature on the
strength, elasticity and adhesion of
the film.
 Use mild drying condition.
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7.  CRATERING
• 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 Remedies
 Inefficient drying.
 Higher rate of application of coating
solution.
 Use efficient and optimum drying
conditions.
 Increase viscosity of coating
solution to decrease spray
application rate.
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Exposed tablet surface
area due to craters

8.  PITTING
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.
Causes Remedies
• Inappropriate drying (inlet air )
temperature.
 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.
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9.  BLOOMING
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
 High concentration and low
molecular weight of plasticizer.
 Decrease plasticizer concentration
and increase molecular weight of
plasticizer.
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Dull coat

10.  BLUSHING
• It is defect best described as whitish specks or haziness in the film
• Reason: It was thought to be due to precipitation of polymer worsened by the
use of high coating temperature.
Causes Remedies
• High coating temperature.
• Use of sorbitol in formulation
which causes largest fall in the
thermal gelation temperature of the
polymers
 Decrease the drying air
temperature.
 Avoid use of sorbitol with the
polymers.
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Whitish specks

11.  ORANGE PEEL/ROUGHNESS
• 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 Remedies
• Rapid Drying
• High solution viscosity
 Use mild drying conditions.
 Use additional solvents to decrease
viscosity of solution.
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12.  STICKING AND PICKING
• Sticking involves sticking of the tablets with each other and with pan walls.
• Picking is the case of sticking involves adhering of some portion of coated
layer to pan or to another tablet at the point of contact.
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Causes Remedies
• Higher rate of application of coating
solution
• Inefficient drying.
 Use optimum and efficient drying
conditions.
 Increase the inlet air temperature.
 Decrease the rater of application of
coating solution by increasing
viscosity of coating solution.

13.  COLOUR VARIATION:
• 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.
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Causes Remedies
• Improper mixing, uneven spray
pattern, insufficient coating,
migration of soluble dyes-
plasticizers and other additives
during drying.
 Go for geometric mixing,
reformulation with different
plasticizers and additives or use
mild drying conditions.

14.  BRIDGING:
• Coating fills in the letter or logo on the tablet .
Causes Remedies
• Poor logo design
• Improper application of coating
solution
• Improper atomization pressure
• High percentage of solid in coating
solution
• High coating viscosity
 Increase plasticizer contents or
change plasticizer concentration
 Reduce viscosity of coating
solution
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15.  EROSION
• The coating solution gets removes from the surface of the tablets due to
friction amongst themselves.
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Causes Remedies
• Over-wetted tablet surface
• Inadequate drying
• Lack of tablet surface strength
 Control drying rate & temparature

16.  TWINNING:
• This term is used when two tablets stick together.
• Reason: Common problem when shape of tablet is capsule shaped.
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Causes Remedies
• Coating suspension can not be
evaporated.
 Reducing spray rate
 Increasing pan speed
**In some cases, it is necessary to alter the design of the tooling by very slightly changing
radius.
The change is almost impossible to see (minor), but it solves the twinning problem.

17. Critical parameters to be optimized during coating
• Distance of sprayer from bed (nozzle spacing)
• Spray pattern,
• Spray speed,
• Droplet size,
• Drying temperature (Inlet-outlet)
• Speed of air
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18.  References:
1. Lachman L, Lieberman HA, Joseph LK. The Theory and Practice of Industrial
Pharmacy. Varghese Publishing House; Mumbai; Third Edition: 297-321, 293-345,
346-373.
2. Remington J. Remington: The Science and Practice of Pharmacy; Nineteenth
Edition: Volume II 1615-1641
3. Abhinav singh Rana, S.L. Hari kumar, Manufacturing defects of tablets - a review,
Journal of Drug Delivery & Therapeutics; 2013, 3(6), 200-206
4. Aulton M. Pharmaceutics: The Science of Dosage Form Design; International
Student Edition: 304-321, 347-668.
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