Tablet coating defetcs 1


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Tablet coating defetcs 1

  1. 1. Tablet Coating Defetcs By – Anika Tabassum Bristy B.Pharm Student North South University
  2. 2. 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
  3. 3. 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 • • • • • • Twinning Color variation Orange peel Roughness Agglomeration Chipping • • • • • • Blistering Bridging Cracking Picking Capping Pitting • Splitting • Flaking • Mottled color • Erosion • Blushing
  4. 4. 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
  5. 5. 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
  6. 6. 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
  7. 7. 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.
  8. 8. 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 . Chipping o 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 .
  9. 9. 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
  10. 10. 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
  11. 11. 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 plastisizer . increase MW & concentration of
  12. 12. Erosion Cause : • Over-wetted tablet surface • Inadequate drying • Lack of tablet surface strength Remedy – Control drying rate & temparature Pitting It is defect whereby pits occur in the surface of tablet core Cause • 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
  13. 13. Color variation Two types of color variation – Individual Tablet Color variation, • Whole Batch Color Variation • Cause :     Remedy : improper mixing, uneven spray pattern, insufficient coating migration of soluble dyes , plasticizer and other additives during drying. • Use of lake dyes eliminates dye migration. • A reformulation with different plasticizer and additives is the best way to solve film instability.
  14. 14. 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.
  15. 15. 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.
  16. 16. References :     Pharmaceutical Forms – Tablets Dosage - Larry L. Augsburger, Stephen W. Hoag  Tablet Coating by Air Suspension - Clarence James Endicott