Tablet Coating Defects and Remedies

Tablet Coating is a very critical Process in pharmaceutical industries because it is said that coating is an art & it depends on the skills of the tablet coating operator to make the process trouble-free by adjusting the parameters according to the physical situation.The tablet coating process is not always as smooth as it looks, some issues are faced during the process of tablet coating & in this article, we will learn about various tablet coating defects, their reasons & solutions.

Following is the list of tablet coating problems that are usually observed during the tablet coating process

Sticking & Picking
Twinning
Orange Peel Effect
Tablet Color Variation
Weight Gain Issue
Scuffing Of Tablets
Tablet Breakage
Blistering
Blooming
Blushing
Cratering
Pitting
Chipping /Edge Erosion
Surface Erosion
Logo Filling / Spray Drying
Logo Bridging
Film Peeling
Film Cracking
Discolouration

After reading the complete article you will be able to troubleshoot the tablet coating issues.

Sticking & Picking

Sticking & Picking is the tablet coating defect in which tablets stick with each other or with a coating pan & some portion of the film is removed or picked when the tablets are deattached.

Reasons & Remedies Of Sticking & Picking

It is the most common tablet coating problem which may occur because of the following,

Reasons	Solutions
Low Inlet air temperature.	Increase the inlet air temperature.
High spray rate.	Decrease the spray rate.
Low pan speed.	Increase Pan speed to reduce dwell time.
Large droplet size due to low atomization air pressure.	Increase Atomization air pressure.
The less solid content in suspension.	Increase solid content in suspension.
Airflow volume is low.	Increase airflow volume.

Read a Detailed Article On Sticking & Picking

Twinning

Tablet Coating Defects and Remedies is the tablet coating defect where tablets bind with each other at the flat face surfaces. A twinning defect is directly related to tablet shape & this defect is also known as a twin tablet coating defect.

Reasons & Remedies Of Tablet Twinning

Reasons	Solutions
This is commonly observed in capsule Shaped tablets.	Change the shape of tablets.
Too high spray rate.	Reduce the spray rate.
Low Tablet bed temperature.	Increase the inlet air temperature.
Low pan speed.	Increase the pan speed
Large droplet size due to low atomization air pressure.	Increase the atomization air pressure.
Coating suspension contains tacky nature polymers.	Add anti-adherents in coating formulations.
Spray gun to tablet bed distance is short.	Increase the distance between the tablet bed & coating spray guns.

Read a Detailed Article On Tablet Twinning

Orange Peel Effect

Orange Peel Effect is the tablet coating issue which is also known as surface roughness where the surface of the coated tablet is not smooth. It is non-glossy and resembles the peel of an orange.

Reasons & Remedies Of the Orange Peel Effect

Reasons	Solutions
Coating suspension is highly viscous.	Use less viscous coating suspension
Atomization air pressure is very low & forms a large droplet.	Increase atomization air pressure.
Spray gun to tablet bed distance is low.	Increase the distance between spray guns and the tablet bed.
Low inlet air temperature & tablets are not properly warmed.	Increase inlet air temperature to ensure proper drying.
Localized over-wetting due to less gun-to-gun distance.	Increase the distance between spray guns.
The spray rate is very high.	Reduce the spray application rate.

Read Detailed Article On Orange Peel Effect

Tablet Color Variations

This tablet coating defect is also known as a tablet-to-tablet color variation & is observed during the color coating of tablets. As the name indicates in this defect the color of all tablets is not uniform. Uneven Color of tablets in the same batch is observed.

Reasons & Remedies Color Variation

Reasons	Solutions
Low weight gain due to excessive heat.	Reduce the inlet air temperature.
Low weight gain due to high exhaust opening.	Reduce the exhaust opening.
Low spray rate.	Increase spray rate.
Very low pan speed.	Increase Pan speed.
High spray gun to Tablet bed distance.	Reduce the distance between guns to tablet bed.
The number of Installed spray guns is less.	Use number of spray guns according to pan size.
The Pan baffle design is not good.	Improve coating pan baffle design to improve rotation & mixing.

Read a Detailed Article On Tablet Color Variation

Weight Gain Problem

The weight gain problem is the tablet coating defect in which the standard tablet coating weight is not achieved after the completion of the coating process.

Reasons & Remedies Of Weight Gain Defect

Reasons	Solutions
Low weight gain due to excessive inlet air temperature heat.	Reduce the inlet air temperature.
Low weight gain due to high exhaust opening.	Reduce the exhaust opening.
High Inlet airflow volume.	Reduce the inlet air volume
Low spray rate & increased tablet bed temperature.	Increase the spar rate or reduce the tablet bed temperature.
Increased spray gun to Tablet bed distance.	Reduce the distance between spray guns to tablet bed.
Atomization air pressure is too high.	Reduce the Atomization air pressure.

Read Detailed Article On Tablet Weight Gain Issue

Scuffing Of Film Coated Tablets

Scuffing is the tablet coating defect where black or gray spots appear on the surface of white or light-colored tablets due to the abrasion effect of pan stainless steel & titanium dioxide in coating suspension.

Reasons & Remedies Of Tablet Scuffing

Reasons	Solutions
High concentration of titanium dioxide in the coating formulation.	Reduce the quantity of titanium dioxide. Passivate the pan walls to avoid interaction.
Usually occur in white or light color tablets.	Change the color of tablets
Long processing Hours of the coating process.	Try to reduce the coating process time.
Slow pan speed resulting in sliding rather than thumbing.	Increase Pan speed.
Low pan load & high temperature.	Load pan according to recommended capacity & reduce temperature.

Tablet Breakage

It is the tablet coating defect in which tablets break during the coating process. The tablets may also break during loading or unloading from the coating pan as well.

Reasons & Remedies Of Tablet Breakage

Reasons	Solutions
Tablet hardness is low.	Improve core tablet hardness.
Pan speed is very high.	Reduce pan speed.
The baffle design is not accurate.	Improve baffles design.
Low spray rate.	Increase spray rate.
Core tablets cap or laminate during tumbling.	Change tablet shape or improve binder quantity.
Coating suspension contains less concentration of solid.	Increase solid concentration.
Auto Loading & unloading of tablets.	Manually offload the tablets with great care.

Also Read

Reasons and solutions of tablet capping.

Blistering

Blistering is the tablet coating defect where the film is detached from the tablet surface & forms a blister. It resembles blisters on the skin having a small bubble-like appearance on the tablet surface.

Reasons & Remedies Of Blistering

Reasons	Solutions
Overheating may result in entrapment of gasses or vapor in or under the film.	Avoid overheating the tablet during the coating process.
High-temperature effect on the elasticity & adhesion properties.	Use mild heating during the coating process.
This may occur due to excessive heat at the drying stage.	Use moderate temperature for tablet drying.

Blooming

Blooming is also known as dull filming or Fading of tablet color due to prolonged storage of tablets at high temperatures after coating.

Reasons & Remedies Of Blooming

Reasons	Solutions
Use of high plasticizer concentration in coating suspension.	Reduce the concentration of plasticizer.
Use of low molecular weight plasticizer.	Use higher molecular weight plasticizers.

Blushing

Blushing is the tablet coating defect where white specks are visible on the surface of coated tablets or coated tablets haziness is observed.

Reasons & Remedies Of Blushing

Reasons	Solutions
Precipitation of polymer particles on film due to high temperature.	Don’t overheat the tablets during the coating process.
Use of sorbitol in coating suspension containing HPMC, HPC, or MC results in polymer gelation which results in blushing.	Avoid the use of sorbitol with mentioned polymers.

Cratering

Cratering is the tablet coating defect where a bowl-shaped depression or pit is formed on the tablet surface & it resembles a volcanic crater so it is known as Cratering. Due to crater formation, the core tablet surface becomes visible.

Reasons & Remedies Of Cratering

Reasons	Solutions
Penetration of coating solution to the tablet core especially to the edges & results in core degeneration due to poor drying.	Increase Drying temperature.
The spray rate is too high & the drying temperature is low.	Decrease the spray rate or increase the temperature.

Pitting

Pitting is the tablet coating problem which is also known as Pitts. It is the defect where needle size pin holes appear on the surface of coated tablets without damaging the coating film.

Reasons & Remedies Of Tablet Pitting

Reasons	Solutions
Low tablet hardness.	Improve core tablet hardness.
The spray rate is very high.	Reduce spray rate.
Atomization pressure is very high.	Reduce the Atomization air pressure.
Gun-to-bed distance is low.	Increase gun-to-tablet bed distance.
Pan speed is very high with a low spray rate.	Reduce pan speed or increase spray to form a film.

Tablet Chipping / Edge Erosion

Tablet Chipping also known as Edge erosion is a tablet coating defect where the edges of the tablet are damaged/worn out or chipped & film is also dented at the edges.

Reasons & Remedies Of Tablet Chipping

Reasons	Solutions
Pan-filling is not appropriate according to recommended capacity. (Too low)	Use appropriate pan load according to recommended capacity.
Very high pan speed.	Reduce pan speed.
Very low spray rate.	Increase spray rate.
Inappropriate baffle design resulting in high tumbling force.	Use accurate baffle design to ensure proper rotation.
Coating suspension contains less amount of solid contents.	Increase the concentration of solid content.
Film strength is very low.	Improve coating formulation.
Sharpe tablet edges.	Change the tablet compression tooling design. Break the sharp edges by rotating tablets in the pan before spraying.
High friability of core tablets.	Improve friability by revision of process or formulation.
Old or worn-out tablet tooling.	Use new tooling for compression.

Core Erosion/Surface Erosion

Core erosion also known as surface erosion is the tablet coating defect where the surface of the tablet erodes during the pan rotation or the surface of the tablet is damaged or worn out.

Reasons & Remedies Of Surface Erosion

Reasons	Solutions
Tablet cores contain hygroscopic materials or super disintegrants.	Try to reduce the number of hygroscopic materials.
Very high pan speed.	Reduce pan speed.
Very low spray rate.	Increase spray rate.
Inappropriate baffle design resulting in high tumbling force	Use accurate baffle design to ensure proper rotation.
Coating suspension contains less amount of solid contents.	Increase the concentration of solid content.
Film strength is very low.	Improve coating formulation.
Inappropriate logo or bisect line design.	Change logo design or its placement.
High friability of core tablets.	Improve friability by revision of process or formulation.
Old or worn-out tablet tooling.	Use new tooling for Compression.

Logo Filling Or Spray Drying

Logo Filling / logo In-filling is also known as spray drying tablet coating defect or break lines filling coating defect.

In logo Filling tablet coating defect, the dried coating material is deposited in the logo or breaks lines & fills them resulting in a unreadable logo. This defect is also known as a spray-dried tablet coating defect because the dried coating material deposited on the tablet surface results in a rough tablet surface.

Reasons & Remedies Of Logo Filling

Reasons	Solutions
Coating suspension contains high solid content.	Reduce suspension solid content concentration.
High Inlet air temperature results in rapid evaporation of solvent before reaching to tablet surface(Spray Drying)	Reduce the inlet air temperature to avoid spray drying.
High Atomization air pressure	Reduce Atomization air pressure.
High spray gun to tablet bed distance.	Reduce the distance.
Air entrapment in coating suspension results in foam generation.	Try to avoid aeration of coating suspension. Use of proper mixing & anti-foaming agents.
Inappropriate logo design.	Improve logo design.

Logo Bridging

Logo Bridging is the tablet coating defect where the coating film forms a bridge across the logo or break lines & results in the hiding of the logo & break line or are not clearly visible.

Reasons & Remedies Of Logo Bridging

Reasons	Solutions
The coating suspension has poor plasticizer.	Use a good quality plasticizer.
High spray rate.	Reduce the spray rate.
Low tablet bed temperature.	Increase the tablet bed temperature.
Low Atomization air pressure.	Increase Atomization air pressure.
Core tablet excipients have low adhesion or film has low adhesion.	Improve formulation of core table & use high adhesive coating formulation.
Poor logo design.	Use good quality logo design.

Also Read

GMP vs cGMP and 21 CFR.

Film Peeling

Peeling is the tablet coating problem in which the layer of film is peeled from the tablet surface.

Reasons & Remedies Of Film Peeling

Reasons	Solutions
Overheating of the tablets.	Don’t overheat the tablets
Poor core adhesion properties.	Improve core formulation.
Coating suspension has less quantity of plasticizer.	Increase the amount of plasticizer.
Poor mechanical strength of the film.	Use formulation with improved mechanical strength film.

Film Cracking

Film cracking is the tablet coating defect where visible cracks are observed on the surface of coated tablets.

Reasons & Remedies Of Film Cracking

Reasons	Solutions
Expansion of core tablet due to heat.	Revise formulation or remove mineral ingredients (Calcium carbonate, Calcium phosphate) that are prone to thermal expansion.
Core tablets expand by absorption of water during the coating process.	Avoid or reduce the quantity of water absorbent materials in core tablet (MCC)
The coating formulation is not flexible & has poor mechanical strength.	Change the formulation to withstand expansion.
Excessive heat may result in core expansion.	Reduce temperature.
Core tablets absorb moisture	Increase temperature, and reduce spray rate.

Also Read

Granulation Defects

Discoloration Of Tablet

This tablet coating Issue occurs due to the interaction of excipients in core tablets or due to the migration of ingredients through coating by the effect of heat.

Reasons & Remedies Of Discoloration

Reasons	Solutions
Poor sealing due to low concentration of solid content in suspension resulting in moisture penetrations.	Increasing the amount of solid content.Increases Pan speed or decreases spray rate.
Heat may result in the migration of materials from the core tablet.	Use a mild heating formula.
Moisture penetration on storage.	Use strong coating formulation to avoid moisture penetration.

Images Credit

All Images Source – Google | Images by – Ashland .Resized & combined by author.

Also Read

Share To Others