Tablet Coating Defetcs

By –Anika Tabassum BristyB.Pharm StudentNorth South University

Tablet coating :

Tablet coating is defined as “ covering the tablets with one or more layers of mixture of various substances such as natural or synthetic resins ,gums ,inactive and insoluble filler, sugar, plasticizer, polyhydric alcohol ,waxes , authorized color and some times flavor .’’

Aspects of tablet coating : Avoid irritation of stomach Avoid bad taste Avoid inactivation of drug in the stomach Improve drug effectiveness Reduce influence of moisture Improve drug stability Improve product identity Improve appearance and acceptability

Coating defects :

An ideal coated tablet should be free from any visual defect or functional defect. But some imperfections are seen in the tablet coating for different kinds of reasons .

The imperfections found in tablets coating are known as tablet coating defects .

Some coating defects -

• Blistering

• Bridging• Cracking• Picking• Capping• Pitting

• Twinning• Color variation• Orange peel• Roughness• Agglomeratio

n• Chipping

• Splitting• Flaking• Mottled

color• Erosion• Blushing

Twinning

Two tablets stick together. Most common in capsule

shaped tablets .

Cause –Coating suspension can not be evaporated.

Remedy – Reducing spray rate Increasing pan speed

Cracking Small, fine cracks observed on

the upper and lower central surface of tablets, or very rarely on the sidewall are referred to as ‘Cracks’.

Cause –• Use of higher

molecular weight polymers or polymeric blends

• Higher internal stresses in the film ( more than tensile strength of the film )

Remedy –• Use low molecular weight polymer• Adjust the plasticizer & pigment types and

concentration to minimize internal stresses

Sticking & picking

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

Picking does not occur alone it must have another tablet to be stuck with which called sticking .

Sticking

Picking

Sticking & picking

Cause : Inefficient drying. Higher rate of application of

coating solution Over wetting Excessive film thickness

Remedy : • Reduce liquid

application rate. • Increase in drying air

temperature and air volume.

Blistering It is local detachment of film from the

substrate forming a blister .Cause :Over heating during spraying coating solution

Remedy : use mild drying condition .

Chippingo It is the defect where film become chipped and dented , usually at the edges of tablet .

Cause :• Excessive attrition

during coating process

Remedy : Increase hardness of the film .

Orange peel effects It refers to a coating texture that

resembles the surface of an orange .Cause :• Rapid Drying• High solution viscosity

Remedy :• Use mild drying conditions• Use additional solvents to

decrease viscosity of solution.

Roughness :The surface becomes rough and no glossy .

Remedy:Reduce the degree of atomization

Bridging Coating fills in the letter or logo

on the tablet .

Cause :• Improper formulation• Poor logo design• Improper application of

coating solution• Improper atomization

pressure• High percentage of solid

in coating solution• High coating viscosity

Remedy :• Increase plasticizer contents or change

plasticizer concentration• Reduce viscosity of coating solution

Filling The monogram or bisect is filled

and become narrow .Cause :• Applying too much

solution• Higher solution

applying rate Remedy - Control fluid application rate

Blooming (Hazing/dull film)• Coating becomes dull immediately

or after a prolonged storage . Normally it occurs together with surface roughness.

Cause - using low molecular weight plastisizer .

Remedy - increase MW & concentration of plastisizer .

Erosion

Cause :• Over-wetted

tablet surface• Inadequate drying• Lack of tablet

surface strength

Remedy – Control drying rate & temparature

PittingIt is defect whereby pits occur in the surface of tablet coreCause • Incontinuous spreading of film• temperature of the tablet core is greater than

the melting point of the materials used in tablet formulation

Remedy - control drying temperature

Color variation

Cause : improper mixing, uneven spray pattern, insufficient coating migration of soluble

dyes , plasticizer and other additives during drying.

Remedy :• Use of lake dyes eliminates dye

migration. • A reformulation with different plasticizer

and additives is the best way to solve film instability.

Two types of color variation –• Individual Tablet Color

variation,• Whole Batch Color

Variation

Cratering

It is the defect of film coating whereby volcanic-like craters appears exposing the tablet surface .Cause –• Penetration of the coating solution into the

surface of the tablet

Remedy –• Decrease in spray application rate• Use of optimum and efficient drying

Blushing (whitish specks) The defect best described as whitish specks

or haziness of the film .It is characterized by precipitation of polymer exacerbated by the use of high coating temperature at or above the thermal gelation temperature of the polymers.

Agglomeration

Agglomeration caused by coating suspension cannot be evaporated as soon as it reach the tablet which may be caused from too much inlet coating suspension or too less inlet heat and the unevaporated suspension glue the tablets together. The amount of excess unevaporated suspension is much more than twinning.

Sometimes it can cause by the leaking of coating suspension into the chamber, or too close spraying distance or too low atomizing pressure.

References :

Pharmainfo.netOnimax.netTechceuticals.comPharmaceutical Dosage Forms –

Tablets - Larry L. Augsburger, Stephen W. Hoag Tablet Coating by Air Suspension - Clarence James Endicott