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Tablet:Problems in tablet manufacturingFrom Pharmpedia
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Contents[hide]
1Introductiono 1.1Cappingo 1.2Lamination / Laminatingo 1.3Chippingo 1.4Crackingo 1.5Sticking / Filmingo 1.6Pickingo 1.7Bindingo 1.8Mottlingo 1.9Doubleimpression2Problemsandremedies fortabletcoatingo 2.1Blisteringo 2.2Chippingo 2.3Crateringo 2.4Pickingo 2.5Pittingo 2.6Bloomingo 2.7Blushingo 2.8Colour variationo 2.9Infillingo 2.10Orangepeel/Roughnesso 2.11Cracking/Splitting3KeyPhrases
Introduction(62,63)
Anidealtabletshouldbe free fromany visualdefector functionaldefect. Theadvancements
andinnovationsintabletmanufacturehavenotdecreasedtheproblems,oftenencounteredintheproduction,insteadhaveincreasedtheproblems,mainlybecauseofthecomplexities
oftabletpresses;and/orthegreaterdemandsof quality.
Anindustrialpharmacistusuallyencountersnumberofproblemsduringmanufacturing.Majorityof visualdefectsareduetoinadequate finesorinadequatemoistureinthegranules
ready forcompressionordueto faultymachinesetting. Functionaldefectsaredueto faulty
formulation.Solvingmanyofthemanufacturingproblemsrequiresanindepthknowledgeofgranulationprocessingandtabletpresses,andisacquiredonlythroughanexhaustive
studyandarichexperience.
Here,wewilldiscusstheimperfections foundintabletsalongwiththeircausesandrelatedremedies. Theimperfectionsareknownas: VISUALDEFECTSandtheyareeitherrelatedto
imperfectionsinanyoneormoreofthe following factors:
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I. TabletingProcess
II.Excipient
III.Machine
The defects related to Tableting Process are as follows:
i)CAPPING:Itispartialorcompleteseparationofthetoporbottomoftabletdueair-entrapmentinthegranularmaterial.
ii)LAMINATION:Itisseparationoftabletintotwoormorelayersduetoair-entrapmentinthegranularmaterial.
iii)CRACKING:Itisduetorapidexpansionoftabletswhendeepconcavepunchesareused.
The defects related to Excipient are as follows:
iv)CHIPPING:Itisdueto verydrygranules.
v)STICKING:Itistheadhesionofgranulationmaterialtothediewall
vi)PICKING:Itistheremovalofmaterial fromthesurfaceoftabletanditsadherancetothe faceofpunch.
vii)BINDING
Theseproblems(v, vi, vii)areduetomoreamountofbinderinthegranulesorwetgranules.
The defect related to more than one factor:
viii)MOTTLING:Itiseitherduetoanyoneormoreofthese factors:Duetoacoloured
drug,whichhasdifferentcolourthantherestofthegranularmaterial?(Excipient-related);
impropermixingofgranularmaterial(Process-related);dirtinthegranularmaterialoron
punch faces;oilspotsbyusingoilylubricant.The defect related to Machine
ix)DOUBLEIMPRESSION:Itisdueto freerotationofthepunches,whichhavesomeengravingonthepunch faces.
Further,inthissection,eachproblemisdescribedalong-withitscausesandremedieswhich
mayberelatedtoeitherof formulation(granulation)orofmachine(dies,punchesandentiretabletpress).
Capping
(1,5)
Cappingisthetermused,whentheupperorlowersegmentofthetabletseparateshorizontally,eitherpartiallyorcompletely fromthemainbodyofatabletandcomesoffasacap,duringejection fromthetabletpress,orduringsubsequenthandling.
Reason:Cappingisusuallyduetotheairentrapmentinacompactduringcompression,
andsubsequentexpansionoftabletonejectionofatablet fromadie.
TABLE.27. THECAUSES AND REMEDIESOF CAPPING RELATED TO FORMULATION
(GRANULATION)
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Sr.No.
CAUSES REMEDIES
1.Largeamountof finesinthegranulation
Removesomeorall finesthrough100to200meshscreen
2.Toodryor verylowmoisturecontent(leadingtolossofproper
bindingaction).
Moistenthegranulessuitably. Addhygroscopicsubstancee.g.:sorbitol,methyl-celluloseorPEG-
4000.
3. Notthoroughlydriedgranules. Drythegranulesproperly.
4.Insufficientamountofbinderor
improperbinder.
IncreasingthemountofbinderOR
Addingdrybindersuchaspre-gelatinizedstarch,
gumacacia,powderedsorbitol,PVP,hydrophilic
silicaorpowderedsugar.
5. Insufficientorimproperlubricant.Increasetheamountoflubricantorchangethe
typeoflubricant.
6.Granularmasstoocoldto
compress firm.Compressatroomtemperature.
TABLE.28. THECAUSES AND REMEDIESOF CAPPING RELATED TO MACHINE(DIES,
PUNCHES AND TABLET PRESS)
Sr.No.
CAUSES REMEDIES
1. Poorly finisheddiesPolishdiesproperly.Investigateother
steelsorothermaterials.
2.Deepconcavepunchesorbeveled-edge
facesofpunches.Use flatpunches.
3.Lowerpunchremainsbelowthe faceof
dieduringejection.Makepropersettingoflowerpunchduring
ejection.
4. Incorrectadjustmentofsweep-offblade.Adjustsweep-offbladecorrectlyto
facilitateproperejection.
5. Highturretspeed.Reducespeedofturret(Increasedwell
time).
Lamination / Laminating
(1,5)
Definition: Laminationistheseparationofatabletintotwoormoredistincthorizontallayers.
Reason: Airentrapmentduringcompressionandsubsequentreleaseonejection.
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Theconditionisexaggeratedbyhigherspeedofturret.
TABLE.29. THECAUSES AND REMEDIESOF LAMINATION RELATED TO FORMULATION(GRANULATION)
Sr.No.
CAUSESREMEDIES
1. OilyorwaxymaterialsingranulesModifymixingprocess. Addadsorbentorabsorbent.
2.Toomuchofhydrophobiclubricante.g.:Magnesium-stearate.
Usealessamountoflubricantorchangethetypeoflubricant.
TABLE.30. TheCausesand RemediesofLaminationrelatedtoMACHINE(Dies,Punchesand
TabletPress)
Sr.No.
CAUSES REMEDIES
1.
Rapidrelaxationoftheperipheral
regionsofatablet,onejection fromadie.
Usetapereddies,i.e.upperpartofthedie
borehasanoutwardtaperof3to5.
2. RapiddecompressionUsepre-compressionstep. Reduceturretspeedandreducethe finalcompression
pressure.
Chipping
(1)
Definition: Chippingisdefinedasthebreakingoftabletedges,whilethetabletleavesthepressorduringsubsequenthandlingandcoatingoperations.
Reason:Incorrectmachinesettings,speciallymis-setejectiontake-off.
TABLE.31. THECAUSES AND REMEDIESOF CHIPPING RELATED TO FORMULATION
(GRANULATION) ARE AS FOLLOWS
Sr.No.
CAUSES REMEDIES
1. Stickingonpunch facesDrythegranulesproperlyorincreaselubrication.
2. Toodrygranules.Moistenthegranulestoplasticize. Addhygroscopicsubstances.
3.Toomuchbindingcauseschippingatbottom.
Optimizebinding,orusedrybinders.
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TABLE.32. THECAUSES AND REMEDIESOF CHIPPING RELATED TOMACHINE(DIES,PUNCHES AND TABLET PRESS)
Sr.No.
CAUSES REMEDIES
1.Grooveofdiewornatcompressionpoint.
Polishtoopenend,reverseorreplacethedie.
2.Barreleddie(centerofthediewiderthanends)
Polishthedietomakeitcylindrical
3.Edgeofpunch faceturnedinside/inward.
Polishthepunchedges
4.Concavitytoodeeptocompressproperly.
Reduceconcavityofpunch faces.Use flatpunches.
Cracking
(1)
Definition:Small, finecracksobservedontheupperandlowercentralsurfaceoftablets,or veryrarelyonthesidewallarereferredtoas Cracks.
Reason:Itisobservedasaresultofrapidexpansionoftablets,especiallywhendeepconcavepunchesareused.
TABLE.33. THECAUSES AND REMEDIESOF CRACKING RELATED TO FORMULATION
(GRANULATION)
Sr. No.CAUSESREMEDIES
1. Largesizeofgranules. Reducegranulesize. Add fines.
2. Toodrygranules.Moistenthegranulesproperlyandaddproper
amountofbinder.
3. Tabletsexpand. Improvegranulation. Adddrybinders.
4. Granulationtoocold. Compressatroomtemperature.
TABLE.34. THECAUSES AND REMEDIESOF CRACKING RELATED TOMACHINE(DIES,PUNCHES AND TABLET PRESS)
Sr. No.CAUSES REMEDIES
1. Tabletexpandsonejectionduetoairentrapment.Usetapereddie.
2. Deepconcavitiescausecrackingwhile Usespecialtake-off.
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removingtablets
Sticking / Filming
(1)
Definition: Stickingreferstothetabletmaterialadheringtothediewall.
Filmingisaslow formofstickingandislargelyduetoexcessmoistureinthegranulation.
Reason:Improperlydriedorimproperlylubricatedgranules.
TABLE.35. THECAUSES AND REMEDIESOF STICKING RELATED TO FORMULATION
(GRANULATION)
Sr.No.
CAUSES REMEDIES
1.Granulesnotdried
properly.
Drythegranulesproperly.Makemoistureanalysisto
determinelimits.
2.Toolittleorimproper
lubrication.Increaseorchangelubricant.
3. ToomuchbinderReducetheamountofbinderoruseadifferenttypeof
binder.
4.Hygroscopicgranular
material.Modifygranulationandcompressundercontrolled
humidity.
5. Oilyorwaymaterials Modifymixingprocess. Addanabsorbent.
6. Toosoftorweakgranules.Optimizetheamountofbinderandgranulationtechnique.
TABLE.36. THECAUSES AND REMEDIESOF STICKING RELATED TOMACHINE(DIES,
PUNCHES AND TABLET PRESS)
Sr. No.CAUSES REMEDIES
1. Concavitytoodeep forgranulation. Reduceconcavitytooptimum.
2. Toolittlepressure. Increasepressure.
3. Compressingtoo fast. Reducespeed.
Picking
(1)
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Definition: Pickingisthetermusedwhenasmallamountofmaterial fromatabletisstickingtoandbeingremovedoff fromthetablet-surfacebyapunch face.
Theproblemismoreprevalentontheupperpunch facesthanonthelowerones. The
problemworsens,iftabletsarerepeatedlymanufacturedinthisstationoftoolingbecauseof
themoreandmorematerialgettingaddedtothealreadystuckmaterialonthepunch face.
Reason:Pickingisofparticularconcernwhenpunchtipshaveengravingorembossingletters,aswellasthegranularmaterialisimproperlydried.
TABLE.37. THECAUSES AND REMEDIESOF PICKING RELATED TO FORMULATION
(GRANULATION)
Sr.No.
CAUSES REMEDIES
1. Excessivemoistureingranules.Dryproperlythegranules,determine
optimumlimit.
2. Toolittleorimproperlubrication.
Increaselubrication;usecolloidalsilicaasa
polishingagent,sothatmaterialdoesnot
clingtopunch faces.
3.
Lowmeltingpointsubstances,may
soften fromtheheatofcompressionandleadtopicking.
Addhighmelting-pointmaterials.Usehigh
metingpointlubricants.
4.Lowmeltingpointmedicamentinhighconcentration.
Refrigerategranulesandtheentiretabletpress.
5. Toowarmgranuleswhencompressing.Compressatroomtemperature.Coolsufficientlybeforecompression.
6. Toomuchamountofbinder.
Reducetheamountofbinder,changethe
typeorusedrybinders.
TABLE.38. THECAUSES AND REMEDIESOF PICKING RELATED TOMACHINE(DIES,PUNCHES AND TABLET PRESS)
Sr.No.
CAUSES REMEDIES
1. Roughorscratchedpunch faces. Polish facestohighluster.
2.Embossingorengravinglettersonpunch facessuchasB, A,O, R,P, Q,G.
Designletteringaslargeaspossible.
Platethepunch faceswithchromiumtoproduceasmoothandnon-adherent face.
3. Bevelsordividinglinestoodeep. Reducedepthsandsharpness.
4.Pressureappliedisnotenough;toosoft
tablets.Increasepressuretooptimum.
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Binding
(1)
Definition: Bindinginthedie,isthetermusedwhenthetabletsadhere,seizeortearinthedie. A filmis formedinthedieandejectionoftabletishindered.Withexcessivebinding,thetabletsidesarecrackedanditmaycrumbleapart.
Reason:Bindingisusuallyduetoexcessiveamountofmoistureingranules,lackoflubricationand/oruseofworndies.
TABLE.39. THECAUSES AND REMEDIESOF BINDING RELATED TO FORMULATION
(GRANULATION)
Sr.No.
CAUSES REMEDIES
1.Toomoistgranulesandextrudes
aroundlowerpunch.Drythegranulesproperly.
2. Insufficientorimproperlubricant.
Increasetheamountoflubricantoruseamore
effectivelubricant.
3. Toocoarsegranules.Reducegranularsize,addmore fines,and
increasethe quantityoflubricant.
4.Toohardgranules forthelubricant
tobeeffective.Modifygranulation. Reducegranularsize.
5.Granularmaterial veryabrasiveandcuttingintodies.
Ifcoarsegranules,reduceitssize.
Usewear-resistantdies.
6.Granularmaterialtoowarm,sticks
tothedie.
Reducetemperature.
Increaseclearanceifitisextruding.
TABLE.40. THECAUSES AND REMEDIESOF BINDING RELATED TOMACHINE(DIES,
PUNCHES AND TABLET PRESS)
Sr.No.
CAUSES REMEDIES
1. Poorly finisheddies. Polishthediesproperly.
2.Roughdiesduetoabrasion,
corrosion.
Investigateothersteelsorothermaterialsor
modifygranulation.
3. Undersizeddies. Toolittleclearance.
Reworktopropersize.Increaseclearance.
4.Toomuchpressureinthetablet
press.
Reducepressure.OR
Modifygranulation.
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Mottling
(1)
Definition: Mottlingisthetermusedtodescribeanunequaldistributionofcolouronatablet,withlightordarkspotsstandingoutinanotherwiseuniformsurface.
Reason:Onecauseofmottlingmaybeacoloureddrug,whosecolourdiffers fromthecolourofexcipientsused forgranulationofatablet.
TABLE.41. THECAUSES AND REMEDIESOF MOTTLING
Sr.No.
CAUSES REMEDIES
1.
A coloureddrugusedalong
withcolourlessorwhite-
colouredexcipients.
Useappropriatecolourants.
2.A dyemigratestothesurface
ofgranulationwhiledrying.
Changethesolventsystem,
Changethebinder,
Reducedryingtemperatureand
Useasmallerparticlesize.
3.Improperlymixeddye,
especiallyduring Direct
Compression.
Mixproperlyandreducesizeifitisofalargersizetopreventsegregation.
4.Impropermixingofacolouredbindersolution.
Incorporatedrycolouradditiveduringpowderblending
step,thenadd finepowderedadhesivessuchasacaciaandtragacanthandmixwelland finallyaddgranulating
liquid.
Double impression
(1)
Definition: DoubleImpressioninvolvesonlythosepunches,whichhaveamonogramorotherengravingonthem.
Reason: Atthemomentofcompression,thetabletreceivestheimprintofthepunch.Now,onsomemachines,thelowerpunch freelydropsandtravelsuncontrolled forashortdistancebeforeridinguptheejectioncamtopushthetabletoutofthedie,nowduringthis
freetravel,thepunchrotatesandatthispoint,thepunchmaymakeanewimpressiononthebottomofthetablet,resultingin DoubleImpression.
Iftheupperpunchisuncontrolled,itcanrotateduringtheshorttraveltothe final
compressionstageandcreateadoubleimpression.
TABLE.42. THECAUSES AND REMEDIESOF DOUBLEIMPRESSION
Sr.No.
CAUSE REMEDIES
1. Freerotationofeitherupper -Usekeyingintooling,i.e.insetakeyalongsideof
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punchorlowerpunchduringejectionofatablet.
the punch,sothatit fitsthepunchandpreventspunchrotation.
-Newerpresseshaveanti-turningdevices,whichpreventpunchrotation.
Problems and remedies for tablet coating
Blistering
(1,64)
Definition:Itislocaldetachmentof film fromthesubstrate formingblister.
Reason:Entrapmentofgasesinorunderneaththe filmduetooverheatingeitherduringsprayingorattheendofthecoatingrun.
TABLE.43. THECAUSE AND REMEDYOF BLISTERING
Sr.No.
CAUSE REMEDY
1.Effectoftemperatureonthestrength,elasticityand
adhesionofthe film.Usemilddrying
condition.
Chipping
(1,64)
Definition:Itisdefectwherethe filmbecomeschippedanddented,usuallyattheedgesofthetablet.
Reason:Decreasein fluidizingairorspeedofrotationofthedruminpancoating.
TABLE.44. THECAUSE AND REMEDYOF CHIPPING
Sr.No.
CAUSE REMEDY
1.
Highdegreeofattritionassociatedwiththecoatingprocess. Increasehardnessofthe filmbyincreasingthe
molecularweightgradeofpolymer.
Cratering
(1,64)
Definition:Itisdefectof filmcoatingwhereby volcanic-likecratersappearsexposingthetabletsurface.
Reason: Thecoatingsolutionpenetratesthesurfaceofthetablet,oftenatthecrownwherethesurfaceismoreporous,causinglocalizeddisintegrationofthecoreanddisruptionofthe
coating.
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TABLE.45. THECAUSES AND REMEDIESOF CRATERING
Sr.No.
CAUSES REMEDIES
1.Inefficientdrying.
Useefficientandoptimumdryingconditions.
2.Higherrateofapplicationofcoatingsolution.
Increase viscosityofcoatingsolutiontodecreasesprayapplicationrate.
Picking
(1,64)
Definition:Itisdefectwhereisolatedareasof filmarepulledaway fromthesurfacewhenthetabletstickstogetherandthenpart.
Reason:Conditionssimilartocrateringthatproducesanoverlywettabletbedwhereadjacenttabletscansticktogetherandthenbreakapart.
TABLE.46. THECAUSES AND REMEDIESOF PICKING
Sr.
No.CAUSE REMEDY
1. Inefficientdrying.Useoptimumandefficientdryingconditionsorincrease
theinletairtemperature.
2.Higherrateofapplicationof
coatingsolution
Decreasetheraterofapplicationofcoatingsolutionby
increasing viscosityofcoatingsolution.
Pitting
(1,64)
Definition:Itisdefectwherebypitsoccurinthesurfaceofatabletcorewithoutany visibledisruptionofthe filmcoating.
Reason: Temperatureofthetabletcoreisgreaterthanthemeltingpointofthematerials
usedinthetablet formulation.TABLE.47. THECAUSE AND REMEDYOF PITTING
Sr.No.
CAUSE REMEDY
1. Inappropriatedrying Dispensingwithpreheatingproceduresattheinitiationof
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(inletair)temperature
coatingandmodifyingthedrying(inletair)temperaturesuchthatthetemperatureofthetabletcoreisnotgreaterthanthe
meltingpointofthebatchofadditivesused.
Blooming
(1,64)
Definition:Itisdefectwherecoatingbecomesdullimmediatelyorafterprolongedstorageathightemperatures.
Reason:Itisduetocollectiononthesurfaceoflowmolecularweightingredientsincludedinthecoating formulation.Inmostcircumstancestheingredientwillbeplasticizer.
TABLE.48. THECAUSE AND REMEDYOF BLOOMING
Sr.No.
CAUSE REMEDY
1.
Highconcentrationandlow
molecularweightofplasticizer. Decreaseplasticizerconcentrationandincreasemolecularweightofplasticizer.
Blushing
(1,64)
Definition:Itisdefectbestdescribedaswhitishspecksorhazinessinthe film.
Reason:Itisthoughttobeduetoprecipitatedpolymerexacerbatedbytheuseofhighcoatingtemperatureatorabovethethermalgelationtemperatureofthepolymers.
TABLE.49. THECAUSES AND REMEDIESOF BLUSHING
Sr.No.
CAUSES REMEDIES
1. HighcoatingtemperatureDecreasethedryingairtemperature
2.
Useofsorbitolin formulationwhichcauseslargestfallinthethermalgelationtemperatureofthe
HydroxyPropylCellulose, HydroxyPropylMethyl
Cellulose,MethylCelluloseandCelluloseethers.
Avoiduseofsorbitolwith HydroxyPropylCellulose, HydroxyPropyl
MethylCellulose,MethylCellulose
andCelluloseethers.
Colour variation
(1,64)
Definition: A defectwhichinvolves variationincolourofthe film.
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Reason: Alterationofthe frequencyanddurationofappearanceoftabletsinthesprayzoneorthesize/shapeofthesprayzone.
TABLE.50. THECAUSE AND REMEDYOF COLOUR VARIATION
Sr.No.
CAUSE REMEDY
1.
Impropermixing,unevenspraypattern,insufficientcoating,migrationofsoluble
dyes-plasticizersandotheradditivesduringdrying.
Go forgeometricmixing,reformulation
withdifferentplasticizersandadditivesorusemilddryingconditions.
Infilling
(1,64)
Definition:Itisdefectthatrenderstheintagliationsindistinctness.
Reason:Inabilityof foam, formedbyairsprayingofapolymersolution,tobreak. The foam
dropletsonthesurfaceofthetabletbreakdownreadilyduetoattritionbuttheintagliationsformaprotectedareaallowingthe foamtoaccumulateand set.Oncethe foamhas
accumulatedtoalevelapproachingtheoutercontourofthetabletsurface,normalattritioncanoccurallowingthestructuretobecoveredwithacontinuous film.
TABLE.51. THECAUSE AND REMEDYOF INFILLING
Sr.No.
CAUSE REMEDY
1.Bubbleor foam formationbecauseofairsprayingofapolymersolution
Addalcoholorusespraynozzlecapableof fineratomization.
Orange peel/Roughness
(1,64)
Definition:Itissurfacedefectresultinginthe filmbeingroughandnonglossy. Appearanceissimilartothatofanorange.
Reason:Inadequatespreadingofthecoatingsolutionbeforedrying.
TABLE.52. THECAUSES AND REMEDIESOF ORANGEPEEL/ROUGHNESS
Sr. No.CAUSES REMEDIES
1. RapidDrying Usemilddryingconditions
2. Highsolution viscosityUseadditionalsolventstodecrease viscosityofsolution.
Cracking/Splitting
(1,64)
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Definition:Itisdefectinwhichthe filmeithercracksacrossthecrownofthetablet(cracking)orsplitsaroundtheedgesofthetablet(Splitting)
Reason:Internalstressinthe filmexceedstensilestrengthofthe film.
TABLE.53. THECAUSE AND REMEDYOF CRACKING/SPLITTING
Sr. No.CAUSE REMEDY
1.Useofhighermolecularweight
polymersorpolymericblends.
Uselowermolecularweightpolymersorpolymeric
blends. Alsoadjustplasticizertypeandconcentration.
Key Phrases
y Duringtabletmanufacture,anindustrialpharmacistusuallyencountersmanyproblems.Solvingtheseproblemsrequiresanin-depth
knowledgeoftablet-formulationaswellasmachine-operating
processes.
y CappingandLaminationarethedefectsarisingasaresultofair-entrapmentinthegranularmaterial.
y Chippingisadefectrelatedarisingdueto verydrygranules.y Crackingisduetorapidexpansionoftablets,whendeepconcave
punchesareused.
y Sticking,PickingandBindingaretheimperfectionsrelatedtomoreamountofbinderingranules.
y Mottlingisanimperfectionarisingduetomorethanone factor:acoloureddrug,dirtingranulesortheuseofanoilylubricant.
y Double-Impressionisrelatedtoamachinedefect:itiscausedbythefreerotationofpunchesthathavesomeengravingonthepunch-faces.
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Coating defects:
y Blisteringisrelatedtoentrapmentofgasesinorunderneaththe filmduetooverheatingeitherduringsprayingorattheendofthecoating
run.Useofmilddryingconditionscansolvethisproblem.
y Chippingisrelatedtohigherdegreeofattritionassociatedwiththecoatingprocess.Increaseinhardnessofthe filmbyincreasingthe
molecularweightgradeofpolymercansolvethisproblem.
y Crateringisrelatedtopenetrationofthecoatingsolutionintothesurfaceofthetablet,oftenatthecrownwherethesurfaceismore
porous,causinglocalizeddisintegrationofthecoreanddisruptionof
thecoating.Decreaseinsprayapplicationrateanduseofoptimum
andefficientdryingconditionscansolvethisproblem.
y Pittingisdefectinwhichtemperatureofthetabletcoreisgreaterthanthemeltingpointofthematerialsusedintablet formulation.
Dispensingwithpreheatingproceduresattheinitiationofcoatingand
modifyingthedrying(inletair)temperaturecansolvethisproblem.
y Bloomingordull filmisgenerallybecauseofhigherconcentrationandlowermolecularweightofplasticizer.Souselowerconcentrationand
highermoleculargradeofplasticizer.
y Blushing/Whitishspecks/Hazinessofthe filmisrelatedtoprecipitationofpolymerexacerbatedbytheuseofhighcoatingtemperatureator
abovethethermalgelationtemperatureofthepolymers.
y Colour variationisbecauseofimpropermixing,unevenspraypattern,insufficientcoatingormigrationofsolubledyesduringdrying.
Geometricmixing,milddryingconditionsandreformulationwith
differentplasticizerscansolvethisproblem.
y Infillingisbecauseofbubble/foam formationduringairsprayingofapolymersolution. Additionofalcoholoruseofspraynozzlecapableof
fineratomizationcansolvethisproblem.
y Orangepeel/Roughnessisrelatedtoinadequatespreadingofthecoatingsolutionbeforedrying.Sodecreasein viscosityofcoating
solutioncancounterthisdefect.
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