BYARJUN NARALA
M.PHARMACY, I SEM
DEPARTMENT OF PHARMACEUTICSUNIVERSITY COLLEGE OF PHARMACEUTICAL SCIENCES
KAKATIYA UNIVERSITYWARANGAL.
CONTENTS
Introduction
Defects in Tablets
Defects in sugar coated tablets
Defects in film coated tablets
Conclusion
References
INTRODUCTION In the normal process of developing formulations,
and in the routine manufacture of tablets, variousdefects are observed. Sometimes, the source of theproblem or the defect is the formulation, thecompression equipment, or a combination of the two.
Some defects are noticed immediately duringmanufacturing but others may be noticed duringstorage as in the case of capping.
DEFECTS IN TABLETS
CAPPING AND LAMINATION
PICKING AND STICKING
MOTTLING
DOUBLE IMPRESSIONS
BLACK SPECKS
CHIPPING AND SPLITTING
CAPPING AND LAMINATION
Capping is defined as the partial or complete separation of thetop or bottom crowns of a tablet from the main body of thetablet.
Lamination is the separation of a tablet into two or moredistinct layers.
These processing problems are readily apparent immediatelyafter compression or may occur hours or even days later.
Subjecting tablets to the friability test is the quickest way ofrevealing such problems.
CAPPING AND LAMINATION
CAUSES AND CORRECTIVE ACTIONS
Air entrapment
Reduce press speed
Precompress granulation
Reduce quantity of fine particles in the granulation
Taper dies
Ensure that punch-to-die clearance is correct
Excessive pressure
Reduce tablet weight and/or increase its thickness withinallowable tolerances
Adjust pressure
CAUSES AND CORRECTIVE ACTIONSToo rapid expansion of tablet upon ejection
Taper dies
Poor granulation
Increase quantity of binder; use strong binder
Excessively dry granulation
Increase lubricant
Excessive lubrication of granulation
Decrease lubricant; blend all ingredients before addinglubricant
CAUSES AND CORRECTIVE ACTIONSPunch cavity too deep
Use punches with less concave depth
Punch tips worn
Refurbish or replace punches
Lower punch set too low at tablet take-off
Set lower punch tip flush with top of die
Tablet take-off bar set too high
Adjust take-off bar
PICKING AND STICKING Picking refers to a tablet material
being removed from the tabletssurface by a punch.
It is of particular concern whenpunch tips have engraving orembossing.
Tablet materials adhering topunches can accumulate to thepoint of obliterating the tipdesign.
Sticking refers to a tablet materialadhering to the die wall.
It results in the buildup ofmaterial on punch faces.
CAUSES AND CORRECTIVE ACTIONSExcessive moisture
Check moisture content of granulation; drying
Check room humidity
Presence of low-melting-point substances
Dilution with higher-melting-point materials
Insufficient compaction force
Reduce tablet weight and/or increase its thickness withinallowable tolerances
Inadequate lubrication of granulation
Check and/or adjust level of lubricant used
CAUSES AND CORRECTIVE ACTIONSPunch face condition: pits on punch faces and/or improper draft
on embossing
Try repolishing punch faces
Try chrome-plating of punch faces
Poor embossing design
Redesign embossing per TSM guidelines, or consult toolingsupplier
MOTTLING
Unequal distribution of color on a tablet, with light or darkareas standing out in an otherwise uniform surface.
Causes and corrective actions:
Drug whose color differs from the tablet excipients or a drugwhose degradation products are colored.
Use of colorants
Migration of dyes to the surface of granulation during drying
Change the solvent system
Reduce the drying temperature
Grind to a small particle size
CAUSES AND CORRECTIVE ACTIONS
High moisture content of granulation Dry granulationOversized granulation particles Reduce particle sizeContamination of granulation, usually by grease or oil Check oil seals on upper punch guides Fit oil/dust caps to upper punches Reduce lubrication of upper punches to an acceptable levelContamination of granulation from chutes or feed hoppers Clean and reset components correctly
DOUBLE IMPRESSION
This problem is encountered with punches that have amonogram or other engraving on them.
Causes and corrective actions:
Rotation of punches
Adjust antiturning devices
Use keyed punches
DIRT IN PRODUCT (BLACK SPECKS) :
Dust,dirt,or press lubrication in the granulation
Clean press more frequently
Excessive or wrong press lubrication
Use proper punch dust caps
Rubbing of feeder components
CHIPPING OR SPLITTING
Poor surface finish on punch tips; worn punches and dies
Poor tooling design (e.g., sharp embossing or bisect lines)
Polish punch tips; replace punches and dies
DEFECTS IN SUGAR COATED TABLETS
CHIPPING OF COATINGS:
Sugar coatings are inherently brittle and thus prone to chipping ifmishandled.
Excessive use of insoluble fillers and pigments tends to increasethe brittleness of sugar coatings.
Avoid them where ever it is possible
Addition of small quantities of polymers(such ascellulosics,polyvinylpyrrolidine,acacia,or gelatin) to improvestructural integrity.
CRACKING OF COATINGS:
Tablet cores that expand, either during or after coating, arelikely to cause the coating to crack. Such expansion may result from
1.Moisture absorption by the tablet core.2.By stress relaxation of the core after compaction.
Moisture sorption can be minimized by appropriate use ofseal coat.
Expansion due to post compaction stress relaxation can beresolved by extending the time between the compaction eventand commencement of sugar coating.
TWINNING (OR BUILD OF MULTIPLES)
By their very nature, sugar-coatingformulations are very sticky,particularly as they begin to dry, andallow adjacent tablets to stick together.
Build up of multiples really becomes aproblem when the tablets being coatedhave flat surface which can easily comeinto contact with one another.
Troublesome with high-dose, capsule-shaped tablets that have high edgewalls.
Appropriate choice in tablet punchdesign can be effectively used tominimize the problem.
UNEVEN COLOR
Uneven distribution of color, particularly with the darkercolors, is often visually apparent, and thus a major cause ofbatch rejection.Poor distribution of coating liquids during application Uniform mixing of tablets in the coating process Addition of sufficient coating liquidsColor migration of water-soluble dyes while the coating is
drying Change the solvent system Reduce the drying temperature Grind to a small particle size
Unevenness of the surface of the subcoat
Achieve desired surface smoothness
Washing back of pigment-colored color coatings
Replace aluminium lakes
Use combinations of dyes and pigments
Excessive drying between color applications
Reduce rate of drying
Reduce drying temperature
BLOOMING AND SWEATING
Residual moisture in finished sugar-coated tablets can oftenbe a problem. over a period of time, this moisture can diffuseout and affect the quality of the product.Moderate levels of moisture egress cause the polish of the
product to take on a fogged appearance, a phenomenon oftentermed blooming.At higher levels of moisture egress, the moisture may appear
like beads of perspiration on the tablet surface, a phenomenonoften termed sweating.Sweating can be much more serious, since tablets stored in
closed containers will ultimately stick together. Obtain appropriate levels of moisture.
MARBLING
To achieve a high-quality, sugar coated product it is importantto ensure that color is uniformly distributed in the color layer,and at the end of the application of the color coating that asmooth coating surface is obtained.
Failure to achieve the requisite smoothness often results in amarbled appearance on polishing.
This problem occurs as the result of the collection of wax in thesmall surface depressions of a rough coating and is particularlyevident with darker colors.
Check for smooth surface at the end of color coating.
DEFECTS IN FILM COATED TABLETSPICKING:
It results when the coating on two adjacent tablets is notsufficiently dry before contact between them occurs.
As the partially dried coating is extremely tacky, once the twotablets make contact they adhere to one another.
Once the coating has dried they break apart later under theinfluence of attrition.
In extreme cases the tablets may become permanently gluedtogether so that twinning occurs.
Over wetting typically occurs when the spray rate is excessivefor the drying conditions in the process.
Adjust the spray rate
Adjust the temperature of drying
Check for the proper functioning of the spray guns
Certain types of coating formulations(e.g., those based onhydroxypropylcellulose, and several of the acrylic aqueouslatex coating systems) are inherently tackier during application.
Replace with other polymer systems.
ORANGE PEEL(ROUGHNESS) Inadequate spreading of the coating
solution before drying causes a bumpy ororange-peel effect on the coating.
This indicates that spreading is impededby too rapid drying or by high solutionviscosity.
This is caused by process conditionswhich include low spray rates coupledwith excessive drying conditions and useof excessive atomizing air pressures.
Adjust the spray rate and dryingconditions
Coating liquids with high viscosities Thinning the coating solution with
additional solventsIn brief optimize the coating process.
EDGE WEAR(CHIPPING)
Tablet edges are often exposedto attritional effects, so fractureat this point results in parts ofthe surface being exposed,referred as chipping.Seen with brittle film coatings
that offer insufficient protectionto tablet edges. Addition of small quantities of
polymers(such ascellulosics,polyvinylpyrrolidine,acacia,or gelatin) to improvestructural integrity.
FILM CRACKING
Cracking of film coating occurs when the internal stressexceeds the tensile strength of the coating.The problem is exacerbated when significant differences exist
between the thermal expansion coefficients for the core andcoating.Totally unacceptable for products where the applied coating is
a major factor in modifying drug-release characteristics. Minimize the internal stresses by adjusting the plasticizer type,
pigment type and their concentration. Increase the tensile strength of the film by using high
molecular-weight polymers or polymer blends.
FILM PEELING
During application of aqueouscoating formulations, cohesivefailure(cracking) of the coatingoccurs.This coating may peel back from
the surface of the substrate andresult in peeling.Cohesive and adhesive failure(
both linked to internal stress) Increase the tensile strength of
the film Decrease the internal stress
BRIDGING OF LOGOS(INTAGLIATIONS) This phenomenon occurs when a
component of the internal stressbecomes sufficiently high so as tocause partial or complete detachmentof the coating ( from the substrate) inthe region of logo.
As a result of such detachment, thefilm is able to shorten and thuspartially relieve the stress within thefilm.
This defect can be so severe that themonogram or bisect is completelyobscured.
Improve film adhesion by adjustingplasticizer content
Appropriate design of tablet puncheswith respect to logo
IN-FILLING OF LOGOS
In-filling of logos typically occurs during the spray applicationof aerated aqueous film-coating solutions.
When a foamy coating solution impinges on a regular part ofthe tablet surface it will, under the shear forces generated, forma film with normal characteristics.
Those droplets of coating liquid that reside in the logo, beingprotected from shear forces at the surface, gradually dry toform a solid foam that eventually obliterates the bisect.
Judicious monitoring of the fluid application rate and thoroughmixing of the tablets in the pan prevent filling.
BLISTERING
When coated tablets require further drying in ovens, too rapidevaporation of the solvent from the core and the effect of hightemperature on the strength, elasticity, and adhesion of the filmmay result in blistering.
Use milder drying conditions.
CONCLUSION Tablets are widely used dosage forms but defects in
aesthetic appearance may lead to the rejection of theiradministration by the patient.
From the manufacturer point of view these defects maylead to reworking or rejection of the batch.
Although many of these defects may be purely cosmeticsome of them are totally unacceptable.
So a proper attention by the manufactuer on the source ofdefects and their orderly corrections is required.
REFERENCES
Herbert A. Lieberman, Leon Lachman, Joseph B. Schwartz,Pharmaceutical dosage forms : Tablets, Second Edition,vol 3.
Herbert A. Lieberman Leon Lachman, Theory and Practice ofIndustrial Pharmacy, 2009.
James Swarbrick, James C. Boylan, Encyclopedia ofPharmaceutical technology, Volume 15, 1996.
James Swarbrick, Encyclopedia of Pharmaceutical technology,Third Edition, Volume 6, 2007.
Website:
www.pharmainfonet.com
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