TABLET COATING

This presentation deals with the description of tablet coating and all the types of tablet coating.

1. UNIT II B. TABLET COATING Ms. TENY SARA THOMAS MOUNT ZION COLLEGE OF PHARMACEUTICAL SCIENCES AND RESEARCH, ADOOR, KERALA ASSISTANT PROFESSOR B.PHARM FIF TH SEMESTER FORMULATIVE & INDUSTRIAL PHARMACY

2. CONTENTS Introduction Types of Tablet Coating Coating Materials Coating Composition Coating Equipments Coating Defects

3. INTRODUCTION Tablet Coating :- is the last critical step in the Tablet Production Cycle. Tablet coating is the process in which the tablet surfaces become covered with a tacky polymeric film to achieve specific benefits. The successful application of coating to tablet provides the visual characteristics for the product, thus the quality of the product may be judged on this final production step.

4. Need of Tablet Coating This additional step of tablet coating in the tablet manufacturing process, increases the cost of the product. Therefore, the decision to coat a tablet can be based on the following reasons :- Mask unpleasant taste, odour, or colour of a drug. Provide physical and chemical protection for the drug. Improve pharmaceutical elegance by use of special colours and contrasting printing. Control the release of the drug from the tablet. Protect the drug from gastric environment of the stomach with an acid resistant enteric coating. Incorporate another drug in the coating to avoid chemical incompatibilities or to provide sequential drug release.

5. TYPES OF TABLET COATING 6 MAJOR TYPES SUGAR COATING FILM COATING ENTERIC COATING VACUUM FILM COATING ELECTROSTATIC COATING DIP COATING

6. SUGAR COATING Sugar coating :- is the process of depositing layer that an be either coloured or uncoloured to the tablets. This process is a step wise process. The operator determines :- the quantity of the coating solution to add, the method and the rate of pouring of coating solution, when to apply the dry air and how long or how fast the tablets should be tumbled in the coating pan.

7. The steps involved in sugar coating are :-

8. 1. WATER PROOFING / SEAL COATING Seal Coating :- done to provide moisture barrier to the core tablet and harden the tablet surface. Helps to maintain physical and chemical stability of the finished product. Materials used in Seal coating :- Shellac , Zein Shellac :- effective sealant but it may slow down the disintegration & dissolution time which affects the therapeutic release. Zein :- an alcohol soluble protein derivative from corn is another effective sealant.

9. 2. SUB COATING Sub Coating :- applied to round the edges and build up the tablet size. Two methods are used for this sub coating. Applying a sticky binder solution to the tablets followed by dusting of sub coating powder and then drying. This is repeated until the desired size is achieved. Sub coating powders include :- calcium carbonate, powdered sucrose, powdered dry gum acacia. Another method, is the spraying process, where a sub coating powder suspension containing both the binder and the insoluble powder is sprayed intermittently on the tablet bed

10. 3. SYRUP COATING or SMOOTH COATING Syrup coating or Smooth Coating :- done to cover and fill the imperfections in the tablet surface caused by the sub coating step, so as to increase the tablet dimension to a predetermined level. Several coats of simple syrup solution (60-70%) are applied. Syrup solution contains pigments, starch, gelatin , or acacia. Syrup solutions are also called grossing syrups .

11. 4. COLOURING Colouring :- gives colour an finished size of the tablet. A thin sucrose solution containing the requisite colouring materials is used for the process. Water soluble dyes or water insoluble pigments can be used. Water insoluble dyes are preferred over water soluble dyes as water soluble dyes may cause mottling.

12. 5. POLISHING Polishing :- Tablets after colouring, they are polished to give desired luster to the tablet. Polished by carefully applying, powdered wax { beeswax or carnauba} or warm solutions of these waxes in naphtha or suitable volatile solvents.

13. FILM COATING Film coating :- is the process of placing a thin, skin tight coating of plastic like material or polymer over the compressed tablet. Film coating solutions can be non – aqueous or aqueous. Volatility of the solvent enables the film to adhere quickly to the surface of tablets.

14. Ideal Characteristics of a Film Coating Material Adequate solubility in coating solvent and in the GI fluid. Stability in presence of heat, light, moisture, air, etc. Compatibility with addictives present, non –toxic, inert, resistant to cracking, withstand normal handling. Compatibility to obtain a elegant product. Ease of printing procedure on high speed equipment.

15. Film Coating Materials Film formers Alloying substance Solvent system Plasticizer Opaquant extenders Colourants Glossants Anti – Oxidants Flavours & Sweetners Surfactants Anti – Microbials

16. 1. FILM FORMERS Capable of producing smooth thin film reproducible under conventional coating conditions and applicable to variety of tablet shapes. Polymers are mainly used as film formers. E.g – cellulose acetate phthallate , hydroxy propyl methyl cellulose, sodium carboxy methyl cellulose.

17. 2. ALLOYING SUBSTANCE Provides water solubility or permeability to the film to ensure penetration by body fluids and therapeutic availability of the drug. E.g – polyethylene glycol

18. 3. SOLVENT SYSTEM Is mainly used for the dissolving of solvent and to allow the spread of other components over the tablets while allowing rapid evaporation to permit speedy operation. E.g – ethanol, methanol, chlorinated hydrocarbons, methylene chloride.

19. 4. PLASTICIZER Gives elasticity and flexibility to the coat material that increases the durability. Plasticizers act by breaking down the polymer – polymer bond and reducing the films brittleness. E.g – castor oil, propylene glycol, polyethylene glycol.

20. 5. OPAQUANT EXTENDERS Added to give more pastel colours and enhance film coverage. E.g – titanium dioxide, talc, magnesium carbonate. 6 . COLOURANTS Added to enhance visual appeal of the product and identify the product . E.g – sunset yellow, tartrazine , erythrosine .

21. 7. GLOSSANTS Added to give luster to the tablet without polishing. E.g – beeswax. 8. ANTI - OXIDANTS Added to stabilize a dye system . E.g – oximes , phenols.

22. 9. FLAVOURS & SWEETNERS Added to mask unpleasant taste and odour. E.g – aspartame, water soluble pineapple flavour. 10 . SURFACTANTS Added to solubilise insoluble ingredients in the coating . E.g – spans and tweens . 11 . ANTI - MICROBIALS Added to prevent microbial growth in coating composition. E.g – alkylisothiazolinone , carbamates .

23. ENTERIC COATING Enteric coating :- is the process of coating done to the tablet to protect from the acidity of stomach and usually disintegrate the tablet in the intestine. Reasons of Enteric Coating :- Protect acid labile drugs from GI fluid. Prevent gastric distress or nausea due to irritation from a drug. Deliver drugs intended for local action in the intestines. Deliver drugs that are optimised to absorb in the small intestine. Provide delayed release

24. Ideal Characteristics of a Enteric Coating Material Resistant to gastric fluids Ready susceptibility or permeability to intestinal fluids. Compatibility with coating solutions. Formation of continuous film Non toxicity, low cost, ease of application Enteric coating materials :- cellulose acid phtahllate , shellac and its derivatives

25. ELECTROSTATIC COATING Electrostatic coating :- used to apply coat conductive substances. Coating material contains conductive ionic species of opposite charge is sprayed on to the charged substrate.

26. DIP COATING Dip coating :- coating is applied to the tablet cores by dipping them into the coating solution. Wet tablets are dried in an conventional manner in coating pans

27. VACUUM FILM COATING Vacuum Film Coating :- is a coating procedure that employs a specially designed baffled pans. Pan is water jacketed. Sealed to achieve a vacuum system. Tablets are placed in the sealed pan. Coating solution is then applied to tablets with an airless spray system.

28. The coating materials is a physical deposition of the material on the tablet substrate, or they form a continuous film with a wide variety of properties depending on the composition of the coating formulations. Examples of physical deposition of the coating materials are the techniques of sugar, shellac, wax or polymer coatings TABLET COATING MATERIALS

29. Coating Materials Hydroxypropyl methylcellulose USP {HPMC} Methyl hydroxyethylcellulose {MHEC} Hydroxypropylcellulose {HPC} Ethylcellulose {EC} Sodium carboxymethylcellulose {Na CMC} Povidone USP Polyethylene glycol {PEG} Acrylate polymers Polyvinyl acetate phthalate {PVAP} Cellulose acetate phthalate {CAP} HPMC Phthalate

30. 1. HYDROXYPROPYL METHYLCELLULOSE USP Prepared by reacting alkali treated cellulose with methyl chloride to introduce methoxy groups and then react with propylene glycol ether groups Available in different viscosity grades Soluble in GI fluid and other solvents. Causes no change in disintegration and bioavailability. Stable in presence of heat, light, moisture or air Easily able to incorporate or other addictives.

31. 2. METHYL HYDROXYETHYLCELLULOSE Prepared by reacting alkali treated cellulose with methyl chloride to introduce methoxy groups and then react with ethylene oxide. Available in different grades Structural similarity of MHEC with that of HPMC, shows that MHEC shares the same properties of HPMC.

32. 3. HYDROXY PROPYLCELLULOSE Prepared by reacting cellulose with sodium hydroxide and then react with propylene oxide at an elevated temperature and pressure. Yield flexible films Soluble in water below 40℃, GI fluid, polar organic solvents. Usually used in combination with other polymers

33. 4. ETHYLCELLULOSE Prepared by reacting ethyl chloride or ethyl sulfate with cellulose dissolved in sodium hydroxide. Available in different viscosity grades Insoluble in water below 40℃ & GI fluid. Hence, used in combination with a water soluble addictives. Unplasticized EC films are brittle and require film modifiers to obtain an acceptable film.

34. 5. SODIUM CARBOXY METHYLCELLULOSE Sodium salt of carboxymethylcellulose Prepared by reacting soda cellulose with sodium salt of monochloroacetic acid. Available in different viscosity grades Insoluble in organic solvents but soluble in water to form colloidal solutions. Films are brittle but adhere well to the tablets.

35. 6. POVIDONE USP Synthetic polymer consisting of linear 1-vinyl 2-pyrrolidinone groups. Available in 4 different viscosity grades identified with a “K” value – povidone K 15, K30, K60, and K90 K30 is the most used povidone grade in tablet coating.

36. 7. POLYETHYLENE GLYCOLS Manufactured by the reaction of ethylene glycol with ethylene oxide in presence of sodium hydroxide at an elevated temperature and pressure. PEG of lower molecular weight are liquid at room temperature and used as plasticizer. PEG of higher molecular weight are white, waxy solids at room temperature and used as a coating material.

37. 8. ACRYLATE POLYMERS Are set of polymers commercially under the trademark EUDRAGIT. Eudragit are available in different forms. EUDRAGIT E :- cationic polymer, which is the only form of eudragit which is soluble in GI fluid. EUDRAGIT RL & RS :- copolymers available only as organic solutions and solid materials. These are mainly used as coating material in delayed release tablets. EUDRAGIT L & S :- polymers that are mainly used in coating of enteric coated tablets. They are soluble only in pH 6 & pH 7 respectively.

38. 9. CELLULOSE ACETATE PHTHALATE Widely used as enteric coating material. Dissolves only in pH > 6 Hygroscopic, relatively permeable to water and GI fluids Produces brittle films, hence, combined with hydrophobic film forming materials to achieve a better enteric film.

39. 10. POLYVINYL ACETATE PHTHALATE Manufactured by esterification of partially hydrolysed polyvinyl acetate with phthallic anhydride. Mainly used in coating of enteric tablets.

40. 11. HPMC PHTHALATE Derived from HPMC by esterification with phthalic anhydride. Dissolve at a lower pH than CAP or Acrylate polymers, hence can increase the bioavailability of some drugs.

41. The basic or starting composition of a tablet coating is obtained from the past experience or various sources of literature. The composition of a tablet coating material includes :- Coat or film formers Alloying substance Solvent system Plasticizer Opaquant extenders Colourants Glossants Anti – Oxidants Flavours & Sweetners Surfactants Anti – Microbials TABLET COATING COMPOSITION

42. Most of the tablet coating process uses one of the following 3 major types of equipment TABLET COATING EQUIPMENTS 3 MAJOR TYPES PERFORATED COATING PAN CONVENTIONALCOATING PAN FLUIDIZED BED COATING PAN

43. FLUIDIZED BED COATING PAN Highly efficient coating systems Mainly consists of a vertical chamber Tablets are first filled into the vertical chamber – this process is called Charging. Fluidization of tablets are achieved by upward flow of air. Air stream first enters the column which causes the tablets to rise in the centre. Tablets then fall towards the chambers wall Then the tablets move downwards to enter the air stream again. Coating solutions are applied through spray nozzles that are kept at the top or bottom of the vertical chamber.

44. CONVENTIONAL COATING PAN The standard or conventional coating pan system consists of a circular metal pan mounted on a stand, tilted to an angle of about 45℃. The pan is about 8-60 inches in diameter and is rotated on a horizontal axis by a motor. The coating pan has a provision of hot air through an inlet port. The heated air is directed into the tablet bed and leaves through an exhaust duct. Temperature of the hot air is maintained, so that the chemical constituents are not degraded or decomposed. Coating solutions are applied by ladling or spraying the coating material on to the tablet bed. Spraying produces more faster and even distribution of the coating solution.

45. General Diagram of Standard Coating Pan

46. To increase the spraying efficiency, conventional coating pans were modified into three :- CONVENTIONAL COATING PAN PELLEGRINI SYSTEM IMMERSION SWORD SYSTEM IMMERSION TUBE SYSTEM

47. IMMERSION TUBE SYSTEM In this system, a tube is immersed in the tablet bed. The tube delivers the heated air, and a spray nozzle is built in the tip of the tube . During this operation, the coating solution is applied simultaneously with the heated air from the immersed tube. Heated air flows upwards and leaves the system by the exhaust duct. This enhances the drying efficiency.

48. IMMERSION SWORD SYSTEM In this system, a perforated sword is immersed in the tablet bed. The perforated sword delivers the heated air. During this operation, the coating solutions are applied by an atomised spray system directed to the surface of the rotating pan. Heated air flows upwards from the sword through the tablet bed and leaves the system by the exhaust duct. This enhances the drying efficiency.

49. PELLEGRINI SYSTEM In this system, baffled plates and diffusers are present. Baffled plates are installed to improve blending and turning over the tablet bed. This also helps in distributing the drying air uniformly.

50. PERFORATED COATING PAN In this system, all equipments of this type, consists of perforated or partially perforated drum that is rotated on its horizontal axis in an enclosed housing. Drying air is applied to the tablet bed through different ways in different types of perforated coating pans. In all the types of perforated coating pans, the coating solutions are applied to the surface of the rotating tablet bed through spraying nozzles that are positioned inside the drum. Perforated pan coaters are efficient drying systems with high coating capacity, and can be completely automated for both sugar coating and film coating processes.

51. To increase the spraying efficiency, perforated coating pans were modified into four :- PERFORATED COATING PAN DRIA COATER PAN SYSTEM GLATT COATER SYSTEM ACCELA – COTA SYSTEM HI - COATER PAN SYSTEM

52. ACCELA – COTA SYSTEM Consists of baffles, spray gun and dry air inlet . Baffles – freely mix tablets within drum when rotating. Spray gun – atomizes coating solution. Drying air directed into the drum, is passed through the tablet bed, and is exhausted through perforations in the drum. Process is fast and drying efficiency is also good.

53. HI - COATER SYSTEM Drying air directed into the drum, is passed through the tablet bed, and is exhausted through perforations below the coating drum. This decreases the coating time.

54. DRIA - COATER SYSTEM Drying air is introduced through hollow perforated ribs located on the inside periphery of the drum. As the pan rotates, the ribs dip into the tablet bed, and drying air passes up through and fluidizes the tablet bed. Exhaust is from the back of the pan.

55. GLATT COATER SYSTEM Drying air can be directed from inside the drum through the tablet bed and out an exhaust duct, alternatively with an optional split chambered plenum. Several airflow configurations are possible.

56. TABLET COATING DEFECTS

57. BLISTERING An un-smooth coated surface shows a number of uneven spots called blisters. Causes – effect of temperature on the strength, elasticity and adhesion of the coat. Remedy – use mild drying condition.

58. CHIPPING Defect where film become chipped and dented, usually at the edges of the tablet. Causes – excessive attrition during coating. Remedy – increase hardness of film.

59. CRATERING Defect of film coating where volcanic like craters appears exposing the tablet surface. Causes – penetration of coating solution into the surface of the tablet. Remedy – decrease in spray application rate - use of optimum drying.

60. STICKING & PICKING Defect where isolated areas of films are pulled away from the surface when the tablet sticks together and then part.

61. TWINNING Two tablets stick together. Causes – improper evaporation of coating solution. Remedy – reduce spray rate and increase coating pan speed.

62. BLOOMING Coating becomes dull immediately or after prolonged storage. Causes – using low molecular weight plasticizer. Remedy – increase molecular weight and concentration of plasticizer.

63. BLUSHING Defect where white specks are precipitated on the film Causes – excessive high coating temperature Remedy – decrease drying air temperature.

64. COLOUR VARIATION Either individual tablet colour variation or whole batch colour variation. Causes – improper mixing, uneven spray attern , insufficient coating, mottling of dyes, plasticizer etc. Remedy – use of lake dyes eliminates mottlin , reformulation with different plasticizer and other addictives.

65. BRIDGING / INFILLING Coating fills in the letter or logo on the tablet. Causes – improper formulation, poor logo design, improper application of coating solution, improper atomization pressure, high viscosity of coating. Remedy – addition of alcohol to polymer solution increases dispersion.

66. ORANGE PEEL A surface defect resulting in the film being rough and non - glossy. Appearance is similar to that of a peeled orange Causes – inadequate spreading of coating solution before drying, high solution viscosity Remedy – use mild drying conditions, addition of solvents to reduce viscosity

67. CRACKING Small fine cracks observed on the upper and lower central surface of tablets Causes – use of high molecular weight polymers, high internal stress Remedy – use low molecular weight polymers or polymeric blends.