Flow of Seminar
Introduction to tablet coating
Need to coat a tablet
Problems and Remedies for tablet
Critical parameters for successful
coating of tablets
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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Tablet Coating process
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Fig.2. Schematic representation of tablet coating process
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.
Modifying the drug release profile.
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PROBLEMS AND REMEDIES FOR TABLET COATING
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
Effect of temperature on the
strength, elasticity and adhesion of
Use mild drying condition.
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• It is defect of film coating whereby volcanic-like craters appears exposing the
• 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.
Higher rate of application of coating
Use efficient and optimum drying
Increase viscosity of coating
solution to decrease spray
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Exposed tablet surface
area due to craters
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.
• Inappropriate drying (inlet air )
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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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.
High concentration and low
molecular weight of plasticizer.
Decrease plasticizer concentration
and increase molecular weight of
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• 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.
• High coating temperature.
• Use of sorbitol in formulation
which causes largest fall in the
thermal gelation temperature of the
Decrease the drying air
Avoid use of sorbitol with the
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• 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
• Rapid Drying
• High solution viscosity
Use mild drying conditions.
Use additional solvents to decrease
viscosity of solution.
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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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• Higher rate of application of coating
• Inefficient drying.
Use optimum and efficient drying
Increase the inlet air temperature.
Decrease the rater of application of
coating solution by increasing
viscosity of coating solution.
• 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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• Improper mixing, uneven spray
pattern, insufficient coating,
migration of soluble dyes-
plasticizers and other additives
Go for geometric mixing,
reformulation with different
plasticizers and additives or use
mild drying conditions.
• Coating fills in the letter or logo on the tablet .
• Poor logo design
• Improper application of coating
• Improper atomization pressure
• High percentage of solid in coating
• High coating viscosity
Increase plasticizer contents or
change plasticizer concentration
Reduce viscosity of coating
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• The coating solution gets removes from the surface of the tablets due to
friction amongst themselves.
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• Over-wetted tablet surface
• Inadequate drying
• Lack of tablet surface strength
Control drying rate & temparature
• This term is used when two tablets stick together.
• Reason: Common problem when shape of tablet is capsule shaped.
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• Coating suspension can not be
Reducing spray rate
Increasing pan speed
**In some cases, it is necessary to alter the design of the tooling by very slightly changing
The change is almost impossible to see (minor), but it solves the twinning problem.
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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1. Lachman L, Lieberman HA, Joseph LK. The Theory and Practice of Industrial
Pharmacy. Varghese Publishing House; Mumbai; Third Edition: 297-321, 293-345,
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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