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Different Tablet Coating Defects And Remedies

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15 April 2016 No comments

Coating tablets can be an effective way to give your products a professional edge. Using a tablet coating machine and the correct excipients you can quickly and easily start producing professional tablets.

Blistering

Definition: Blistering occurs when the elasticity and the adhesive properties of the film is compromised resulting to the latter detaching from the tablet’s substrate.

Cause: When the tablet undergoes drying process, higher temperature, over heating during the spraying stage or during the end of the coating, this results in the blistering of the tablet.

Causes and Remedies

CauseRemedy
Effect of temperature on the strength, elasticity and adhesion of the film.Use mild drying condition.

Chipping

Definition: Chipping occurs when the film becomes dented and chipped and this can be usually seen on the edges of the tablet.

Causes: The deformity in the tablet occurs when there is a decrease in the rotation speed in the machinery during the coating process. Another cause would be if the coating solution used lacks the right amount of plasticizer.

Causes and Remedies

CauseRemedy
High degree of attrition associated with the coating process.Increase hardness of the film by increasing the molecular weight grade of polymer.

Cratering

Definition: Cratering happens when a defect on the film’s coating results in craters appearing on the tablet which in turn results in the exposure of the tablet’s surface.

Causes: In certain instances where there is an inefficient drying time or higher volume of coating solution is applied, the solution sips through the tablet’s surface especially in the crown area causing the disruption of the coating and degeneration of the tablet’s core.

Causes and Remedies

CauseRemedy
Inefficient drying.Use efficient and optimum drying conditions.
Higher rate of application of coating solution.Increase viscosity of coating solution to decrease spray application rate.

Picking

Definition: Picking happens when part of the film sticks to the pan resulting to some of the tablet pieces being detached from the core.

Causes: Picking occurs when there is overwetting or excessive film tackiness which results to the tablets sticking to one another.

Causes and Remedies

CauseRemedy
Inefficient drying.Use optimum and efficient drying conditions or increase the inlet air temperature.
Higher rate of application of coating solution.Decrease the rater of application of coating solution by increasing viscosity of coating solution.

Pitting

Definition: The defect happens when a pit occurs in the tablet’s core without any visible signs of disruption in the film coating of the tablet.

Causes: The cause of the pitting occurs when the core’s temperature is higher than the melting point of the materials used during the formulation of the tablet.

Causes and Remedies

CauseRemedy
Inappropriate drying (inlet air ) temperatureDispensing 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.

Blooming

Definition: Blooming is a defect whereby the color of the tablet becomes dull after a prolonged period of storage at a high temperature.

Causes: The tablet’s color becomes dull when the ingredients of the low molecular ingredients formed on the surface. In certain instances the ingredients are or will be plasticized.

Causes and Remedies

CauseRemedy
High concentration and low molecular weight of plasticizer.Decrease plasticizer concentration and increase molecular weight of plasticizer.

Blushing

Description: Blushing occurs when there are white specks in the film or haziness.

Causes: Haziness or white specks appear due to the precipitated polymer and this is aggravated by the use of intense coating temperature or may also be due to the thermal gelation temperature level of the polymers.

Causes and Remedies

CauseRemedy
High coating temperatureDecrease the drying air temperature
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.

Color Variation

Description: A defect that causes tablets to differ in color.

Causes: Color variation may occur when there’s a change in the frequency and look of the tablet but may also be due to the differing sizes of the spray used during the coating process resulting to the uneven color pattern.

Causes and Remedies

CauseRemedy
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.

Infilling

Description: Infilling happens when it solidifies the intagliations haziness.

Causes: The infilling occurs when the foam solution sprayed is unable to break down. The droplets on the tablet’s surface are able to break down however the intagliation forms an area where other foams can accumulate and set in. Once the foam accumulates to a certain level and reaches the outer area, the tablet is then covered continuously with film.

Causes and Remedies

CauseRemedy
Bubble or foam formation because of air spraying of a polymer solutionAdd alcohol or use spray nozzle capable of finer atomization.

Orange Peel (Roughness)

Description: This defect is aptly named as “Orange Peel” due to the appearance of the tablet resembling that of an orange. The surface of the tablet is rough and often nonglossy.

Causes: Orange peel occurs when the tablet’s composition is too much causing a soft tablet. Another factor is when there is high atomization pressure combined with fast spray rates resulting to an uneven coating of the tablet.

Causes and Remedies

CauseRemedy
Rapid DryingUse mild drying conditions
High solution viscosityUse additional solvents to decrease viscosity of solution.

Cracking (Splitting)

Description: Cracking occurs when the film coating the tablet cracks in the crown area or splits around the edges.

Causes: Cracking occurs when the film’s internal stress exceeds the tensile strength of the film.

Causes and Remedies

CauseRemedy
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

  • 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.
  • Capping and Lamination are the defects arising as a result of air-entrapment in the granular material.
  • Chipping is a defect related arising due to very dry granules.
  • Cracking is due to rapid expansion of tablets, when deep concave punches are used.
  • Sticking, Picking and Binding are the imperfections related to more amount of binder in granules.
  • Mottling is an imperfection arising due to more than one factor: a coloured drug, dirt in granules or the use of an oily lubricant.
  • 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:

  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.