Tablet Coating Problems

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Tablet Coating Problems

1.10.2

Problems and Remedies for Tablet Coating

Read about

Blistering , Chipping , Cratering, Picking, Pitting , Blooming, Blushing, Colour variation, Infilling, Orange peel/Roughness, Splitting .

1.10.2.1 Blistering (1,64)

Definition: 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.

Table.43. The Cause And Remedy Of Blistering

Sr. No.

CAUSE

REMEDY

1.

Effect of temperature on the strength, elasticity and adhesion of the film.

Use mild drying condition.

1.10.2.2 Chipping (1,64)

Definition: It is defect where the film becomes chipped and dented, usually at the edges of the tablet.

Reason: Decrease in fluidizing air or speed of rotation of the drum in pan coating.

Table.44. The Cause And Remedy Of Chipping

Sr. No.

CAUSE

REMEDY

1.

High degree of attrition associated with the coating process.

Increase hardness of the film by increasing the molecular weight grade of polymer.

1.10.2.3 Cratering (1,64)

Definition: 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.

Table.45. The Causes And Remedies Of Cratering

Sr. No.

CAUSES

REMEDIES

1.

Inefficient drying.

Use efficient and optimum drying conditions.

2.

Higher rate of application of coating solution.

Increase viscosity of coating solution to decrease spray application rate.

1.10.2.4 Picking (1,64)

Definition: It is defect where isolated areas of film are pulled away from the surface when the tablet sticks together and then part.

Reason: Conditions similar to cratering that produces an overly wet tablet bed where adjacent tablets can stick together and then break apart.

Table.46. The Causes And Remedies Of Picking

Sr.

No.

CAUSE

REMEDY

1.

Inefficient drying.

Use optimum and efficient drying conditions or increase the inlet air temperature.

2.

Higher rate of application of coating solution

Decrease the rater of application of coating solution by increasing viscosity of coating solution.

1.10.2.5 Pitting (1,64)

Definition: 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.

Table.47. The Cause And Remedy Of Pitting

Sr. No.

CAUSE

REMEDY

1.

Inappropriate drying (inlet air ) temperature

Dispensing with preheating procedures at the initiation of coating and 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.

1.10.2.6 Blooming (1,64)

Definition: 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.

Table.48. The Cause And Remedy Of Blooming

Sr. No.

CAUSE

REMEDY

1.

High concentration and low molecular weight of plasticizer.

Decrease plasticizer concentration and increase molecular weight of plasticizer.

1.10.2.7 Blushing (1,64)

Definition: It is defect best described as whitish specks or haziness in the film.

Reason: It is thought to be due to precipitated polymer exacerbated by the use of high coating temperature at or above the thermal gelation temperature of the polymers.

Table.49. The Causes And Remedies Of Blushing

Sr. No.

CAUSES

REMEDIES

1.

High coating temperature

Decrease the drying air temperature

2.

Use of sorbitol in formulation which causes largest fall in the thermal gelation temperature of the Hydroxy Propyl Cellulose, Hydroxy Propyl Methyl Cellulose, Methyl Cellulose and Cellulose ethers.

Avoid use of sorbitol with Hydroxy Propyl Cellulose, Hydroxy Propyl Methyl Cellulose, Methyl Cellulose and Cellulose ethers.

1.10.2.8 Colour variation (1,64)

Definition: 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.

Table.50. The Cause And Remedy Of Colour Variation

Sr. No.

CAUSE

REMEDY

1.

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.

1.10.2.9 Infilling (1,64)

Definition: It is defect that renders the intagliations indistinctness.

Reason: Inability of foam, formed by air spraying of a polymer solution, to break. The foam droplets on the surface of the tablet breakdown readily due to attrition but the intagliations form a protected area allowing the foam to accumulate and "set". Once the foam has accumulated to a level approaching the outer contour of the tablet surface, normal attrition can occur allowing the structure to be covered with a continuous film.

Table.51. The Cause And Remedy Of Infilling

Sr. No.

CAUSE

REMEDY

1.

Bubble or foam formation because of air spraying of a polymer solution

Add alcohol or use spray nozzle capable of finer atomization.

1.10.2.10 Orange peel/Roughness (1,64)

Definition: 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.

Table.52. The Causes And Remedies Of Orange Peel/Roughness

Sr. No.

CAUSES

REMEDIES

1.

Rapid Drying

Use mild drying conditions

2.

High solution viscosity

Use additional solvents to decrease viscosity of solution.

1.10.2.11 Cracking/Splitting (1,64)

Definition: It is defect in which the film either cracks across the crown of the tablet (cracking) or splits around the edges of the tablet (Splitting)

Reason: Internal stress in the film exceeds tensile strength of the film.

Table.53. The Cause And Remedy Of Cracking/Splitting

Sr. No.

CAUSE

REMEDY

1.

Use of higher molecular weight polymers or polymeric blends.

Use lower molecular weight polymers or polymeric blends. Also adjust plasticizer type and concentration.

Key Phrases

O During tablet manufacture, an industrial pharmacist usually encounters many problems. Solving these problems requires an in-depth knowledge of tablet-formulation as well as machine-operating processes.

O Capping and Lamination are the defects arising as a result of air-entrapment in the granular material.

O Chipping is a defect related arising due to very dry granules.

O Cracking is due to rapid expansion of tablets, when deep concave punches are used.

O Sticking, Picking and Binding are the imperfections related to more amount of binder in granules.

O Mottling is an imperfection arising due to more than one factor: a coloured drug, dirt in granules or the use of an oily lubricant.

O Double-Impression is related to a machine defect: it is caused by the free rotation of punches that have some engraving on the punch-faces.

Coating defects:

O Blistering is related to entrapment of gases in or underneath the film due to overheating either during spraying or at the end of the coating run. Use of mild drying conditions can solve this problem.

O Chipping is related to higher degree of attrition associated with the coating process. Increase in hardness of the film by increasing the molecular weight grade of polymer can solve this problem.

O Cratering is related to penetration of the coating solution into 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. Decrease in spray application rate and use of optimum and efficient drying conditions can solve this problem.

O Pitting is defect in which temperature of the tablet core is greater than the melting point of the materials used in tablet formulation. Dispensing with preheating procedures at the initiation of coating and modifying the drying (inlet air) temperature can solve this problem.

O Blooming or dull film is generally because of higher concentration and lower molecular weight of plasticizer. So use lower concentration and higher molecular grade of plasticizer.

O Blushing/Whitish specks/Haziness of the film is related to precipitation of polymer exacerbated by the use of high coating temperature at or above the thermal gelation temperature of the polymers.

O Colour variation is because of improper mixing, uneven spray pattern, insufficient coating or migration of soluble dyes during drying. Geometric mixing, mild drying conditions and reformulation with different plasticizers can solve this problem.

O Infilling is because of bubble/foam formation during air spraying of a polymer solution. Addition of alcohol or use of spray nozzle capable of finer atomization can solve this problem.

O Orange peel/Roughness is related to inadequate spreading of the coating solution before drying. So decrease in viscosity of coating solution can counter this defect.

O Cracking is seen when internal stresses in the film exceeds tensile strength of the film. This is common with higher molecular weight polymers or polymeric blends. So use lower molecular weight polymers or polymeric blends.

About the Author

Dr.Mukesh Gohel's picture
Author: Dr.Mukesh Gohel

Dr. Mukesh Gohel is principal, professor at the LMCP, Ahmedabad served in academics for more than 40 years. He provides training in leading pharmaceutical industries in the areas of Design of Experiments and Quality by Design. His current areas of interest are direct compression and improvement of drug dissolution.

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