TABLET COATING DEPARTMENT OF PHARMACEUTICS CHALAPATHI INSTITUTE OF
TABLET COATING DEPARTMENT OF PHARMACEUTICS CHALAPATHI INSTITUTE OF PHARMACEUTICAL SCIENCES 1
CONTENTS Objectives of tablet coating Tablet properties Coating equipments Types of coating Coating defects Coating parameters References 2
OBJECTIVES OF TABLET COATING Mask the unpleasant taste and odour ex; Quinine drugs, vitamins Provide physical and chemical protection Improve patient acceptability Control the release of the drug from tablet ex; sustained release. 3
Improve the chemical stability of the drug by protecting it against light, air , oxidation and moisture. Protect the drug from gastric environments of stomach Mechanical strength to the tablet core. Maintains the shape of the tablet Identification of a product by the manufacture Pharmacist and by the patient 4
COMPONENTS INVOLVED IN TABLET COATING Tablet Properties : Coating tablet must posses the proper physical characteristics (size , shape) They should easily cascade in the coating pan. They should be resistant to abrasion and chipping. Tablets must be in contact motion during early drying phase. 5
The film coating adheres to all exposed surfaces surface imperfections are not eliminated sugar coating with high solid content, fills many imperfections. 6
COATING EQUIPMENTS COATING PANS STANDARD COATING PANS E. g. ; immersion tube system immersion sword system FLUIDIZEDBED COATER SPRAY EQUIPMENT PERFORATED COATING PANS E. g. ; accela coater pan hi-coater pan dria coater pan glatt coater pan AIRLESS SPRAY AIR SPRAY
COATING PAN Stainless steel – 40 inches in diameter, with variable speed control, with 2 to 3 atomizing nozzles. . 8
Standard Coating pan 9
It is large circular pan of about 8 to 60 inch diameter. It mounted angularly at an angle 40˚ The pan is rotated on its horizontal axis by means of motor. Tablets are coated by spraying the coating solution over the rolling Bed of tablets using spray equipment. Coated tablets are dried by passing hot air into pan through hot Air inlet. Exhausted air is removed through vents or ducts. 10
Immersion Tube System 11
Tube is immersed in to tablet bed Hot air is passed in to tablet bed Air flows In upward direction Exhaust air removed by exhaust vent or duct. Coating material and drying air is applied Simultaneously 12
Immersion sword system Drying air is introduced into the pan through a sword like device having perforations It is immersed into the tablet bed Air flows in upward direction Exhaust air removed by exhaust vent or duct. 13
Accela-Cota System 14
Drying air is passed in to perforated cylindrical pan Air is drawn into tablet bed Application of coating solution on tablet bed by spraying Exhausted air is passed through a duct located At the bottom of the pan 15
Hi-Coater System 16
Function of Hi- Coater is same as accela coater. Drying air is passed in to perforated cylindrical pan through a inlet Coating solution is applied by spraying nozzles Exhausted air is passed through perforated plates present At the bottom of the pan 17
Accela coater Hi coater 18
Dria-Coater System 19
Inside periphery of driacoater is attached with hollow Perforated ribs. It provides multidirectional air flow a) Direct air flow: Air is passed through the ribs located top the pan and exhausted through the ribs located below the tablet bed. b) Reverse flow : Air is passed through the ribs located belo the tablet bed and exhausted through the outlet at the ba Of the pan. 20
Glatt coater It is latest perforated pan coater Drying air passed through tablet bed from the inner side of the drum Exhaust through the out let. Optional split chambered plenum is used to pass the drying air in re Manner through the perforations, for the partial fluidization of tablet 21
Fluidized bed coater (Air Suspension Coater) 22
Fluidized bed coaters are highly efficient drying systems. Fluidization of the tablet mass is achieved in a Coating chamber. More air enters into the center of the chamber Causing table rise in the center. Then they fall down towards the chamber wall and re enters into the air stream. Spray solutions are continuously applied from a spray nozzle Located at the bottom of the chamber. 23
Spray Application systems High – pressure air less system Low – pressure air atomized system Both these systems vary in atomization of liquid. Airless system: liquid is pumped at a high pressure (250 -3000 through a small orifice (0. 009 to 0. 020 inch) Degree of atomization depends upon - Fluid pressure - Orifice size - Viscosity of liquid 24
Air atomized – Liquid is pumped through large orifice (0. 020 to 0. 060 inch) at low pressure (5 -50 psig). Air contacts the liquid stream at the tip of the atomizer to obtain fine spray degree of atomization depends upon - Fluid pressure - Fluid cap orifice - Viscosity of liquid - Air pressure - Air cap design selection of spray system depends upon composition of the coating solution 25
Types of coating Conventional coating process Sugar coating Contemporary coating process Film coating Enteric coating Non – enteric coating Specialized coating process Compression coating Electrostatic coating Vacuum coating 26
Sugar coating is an effective process for the application of thick coating layers, primarily for masking taste. 27
Advantages : Inexpensive and requires simple equipment. Tablets produced are of High quality , smooth & elegant appearance. Dis advantages: Time consuming and lengthy process ( it requires several hours to days to complete) It requires highly skilled manpower. 28
Basic steps involved in sugar coating : polishing Finishing syruping Sub coating sealing 29
SEAL COATING Why seal coating is done ? Need of the seal coating ? To prevent the moisture penetration into the tablet core. It is needed in the pan-ladling process in which localized over wetting of a portion of the tablet bed. Examples: Shellac (natural product derived from scale insects, laccifer lacca) Zein : is an alcohol-soluble protein derivative from corn used as an effective sealant. Lengthening dissolution time not reported 30
SUBCOATING Why sub-coating is necessary? It is applied to round the edges and build up the tablet size & weight ( 50 to 100 %) Steps involved in sub-coating: Binder solution and dusting of subcoating powders are alternately applied on tablets and dried. Same procedure is done until the desired thickness is achieved In spray process the subcoating suspension contains both binder and insoluble powders. Subcoating solutions : Gelatin, Acacia in syrup & water Subcoating powders : Kaolin, Dextrin sugars etc 31
SMOOTHING(SYRUPING OR COLOURING): What is the need of syruping ? It covers the imperfections on the tablet surface caused by the subcoating and imparts the desired colour to the tablet. First syrup coat contains some suspended powders are called grossing syrups, colourants can be added in this step. In the second step, syrup solution containing the dye is applied until the final size and colour is achieved. In the final step, a few clear coats of syrup may be applied. 32
POLISHING: Tablets can be polished in clean standard coating pans or Canvas –lined polishing pans, Polishing can be done by applying powdered wax (bees wax, carnauba) or warm solutions of these waxes in naptha or other suitable Volatile solvents.
FORMULATION OF SUGAR COATING SOLUTION : seal coating Sub coating Syrup coating polishing Zein / shellac Gelatin Colorant Carnauba wax(yellow) Oleic acid Acacia Sub coating powder Bees wax(white) Propylene glycol Sugar cane powder Calcium carbonate Paraffin wax PEG Corn syrup Cane sugar powder Naphtha Methylene chloride syrup Corn starch alcohol Distilled water syrup Distilled water 34
Enteric coating polymers : Cellulose acetate phthalate , acrylate polymers, hydroxypropyl methyl cellulose phthalate, poly vinyl acetate phthalate, Solvents used for sugar coating : Ethanol , methanol, isopropanol , chloroform, acetone Methylene chloride , methylene ethyl ketone, 35
Sugar coated pills 36
FILM COATING Application and deposition of thin film of polymer solution Around the tablet surface Mechanism of Film formation latex particles dispersed in aqueous phase formation of thin film with evaporation of water through film Formation of continuous film 37
Opaquan t extender s colorants Film formers plasticize r solvent COMPOSITION OF FILM COATING 38
Ideal characters of film coating material: Should be soluble in aqueous fluids Solubility required for the intended use e. g. freely water soluble, Slow water soluble , p. H- dependent soluble(enteric coating) Capacity to produce an elegant look Must be stable in the presence of heat, light, moisture, air Should not have color, taste, and odour Non toxic and ease to application Should be resistance to cracking 39
FILM FORMERS (non – enteric materials ): Hydroxy propyl methyl cellulose(HPMC), USP Soluble in organic , aqueous and gastro intestinal fluids. It has flexibility and chip resistance , Polymer has tendency to bridge or fill the tablet surfaces HPMC+Plasticizers or other polymer = eliminate bridging or filling problem Methyl hydroxy ethyl cellulose : It is soluble in fewer organic solvents. 40
Ethyl cellulose , NF It is insoluble in water and gastrointestinal fluids. Ethyl cellulose + HPMC = used in tablet coating Ethyl cellulose + water soluble additives are mostly used In preparing sustained released coating for fine particles and ta Hydroxy propyl cellulose: It is soluble in water , gastro intestinal fluid and organic solvent below 40˚c and insoluble at above 45˚c. Hydroxy propyl cellulose + other polymers = improve film chara 41
Povidone , USP Povidone k 30 is mostly used as binder and also as tablet coati polymer It forms a clear , glossy and hard film. Sodium carboxy methyl cellulose, USP It is easily dispersed in water and form colloidal solutions Insoluble in organic solvents Not used for coating solution. 42
Poly ethylene glycols are used as plasticizers in coating solution Poly ethylene glycols combine with cellulose acetate phthalate forms gastro intestinal soluble films 43
ENTERIC COATING: These are intact with stomach but will dissolve and release the contents of dosage form once it reaches the small intestine. Important reasons for enteric coating: Protects the acid labile drugs from the gastric fluids e. g. enzymes& antibiotics. Prevents gastric distress or nausea due to irritation from a dru e. g. sodium salicylate Intended for local action in the intestine e. g. diclofenac sodium 44
ENTERIC COATING MATERIALS: Cellulose acetate phthalate (CAP) Widely used in the industry. These films are brittle and formulated with hydrophobic film forming materials to achieve better enteric coating. Acrylate polymers: Two trade forms of resins eudragit L and eudragit S, produc gastric acid resistance films Soluble in intestinal fluid at p. H 6 to 7. 45
Hydroxy propyl methyl cellulose phthalate(HPMCP) These polymers are dissolved at p. H at 5 to 5. 5. Poly vinyl acetate phthalate (PVAP) These polymers are similar to hydroxy propyl cellulose phthalate. Ideal enteric polymer should dissolve or become permeable near and above p. H 5. 0 46
SOLVENTS: Primary function of a solvent system is to dissolve or disperse the polymers and other additives to substrate surface. Important Characters: Should dissolve or disperse the polymer system. Should easily disperse other coating solution components. Should be colorless, tasteless, odourless, inexpensive, nontoxic, inert. Should be easily dried. Examples: water, ethanol, methanol, isopropanol, Should be eco -friendly. chloroform, acetone, methyl ketone and methylene chloride. 47
PLASTICIZERS: These are added to film coating to modify the physical Properties of the polymer. Ability to decrease the film brittleness, polymer interactions It gives the stability to film and final coated product Concentration of plasticizer is expressed as the amount of Polymer being plasticized. Recommended level of plasticizer – 1 to 50% by weight of film Former. 48
Examples of plasticizers: Castor oil, propylene glycol of 200 and 400 series and surfactants e. g. Tweens, Spans and organic acid esters. Water- soluble plasticizer : PEG, propylene glycol. Organic- soluble plasticizer : castor-oil and Spans. 49
COLOURANTS: Used to provide distinctive color and elegance to a dosage form Most of colorants are synthetic dyes (soluble) & lakes ( insoluble)Approved by FD&C, D&C. LAKES : derived from dyes by precipitating with Carriers e. g. alumina, talc Lakes contains 10 to 30 % of pure dye content For very light shade, concentration : less than 0. 01 %. For dark shade, concentration : more than 2. 0 % Examples Inorganic materials : iron oxides Natural coloring materials : Anthocyanins, caramel, carotenoids, chlorophyll, indigo, 50 flavones, turmeric and carminic acid.
OPAQUANT EXTENDERS: These are very fine inorganic powders used in the coating solution formulation to provide more pastel colors and increase film coverage. Examples: Titanium di oxide, Silicates (talc, aluminum silicate); Carbonates (magnesium carbonate); Sulfates (calcium sulfate); Oxides (Mg oxides) 51
Film coated pills 52
FILM DEFECTS Sticking and picking Roughness Orange –peel effects Bridging and filling Blistering Hazing/Dull film Colour variation Cracking 53
STICKING AND PICKING: Over wetting and excessive film thickness causes tablets to Stick each other or to the coating pan. On drying a piece of film remain Adhere to pan or tablet gives “picked” appearance of tablet surface, resulting a small portion of tablet core is exposed Remedies Reduce the liquid application rate. Increase in drying air temperature and air volume. 54
ROUGHNESS A rough or gritty surface observed when the coating is applied by spray. Some of the droplets may dry too rapidly before reaching the tablet bed and deposits on tablet surface. Deposition of spray particles instead of fine particles of coating solution Surface roughness also increases with pigment concentration and polymer concentration in the coating solution. Remedies • Moving the nozzle closer to the tablet bed. • Reducing the degree of atomization can decrease the roughness due to spray drying. 55
ORANGE PEEL EFFECT Inadequate spreading of coating solution before drying causes a bumpy or Orange – peel effects On the coating Causes : rapid rate of drying , high solution viscosity. Remedies • Thinning of coating solution with additional solvents ma correct this problem. • Adjust the speed of coating pan 56
BRIDGING During drying the film may shrink and pull away from the sharp corners and bisects, which resulting in “Bridging” of surface dispersion Remedies Increase in plasticizer contents Changing plasticizer FILLING: Application of too much solution, resulting formation of thick film, that fills and narrows the monogram or bisect. Remedies -Judicious monitoring of the fluid application rate. 57
BLISTERING : Local detachment of film from the substrate forming blistering Reason : entrapment of the gases in or underneath of film d Overheating during spraying. Remedie s Maintains the milder drying conditions. 58
HAZING & DULL FILM HAZING (bloom): It occurs when too high processing temperature is used for a particular formulation. DULLING: it is observed when cellulosic polymers are applied at high processing temperature. Also occur if the coated tablets are exposed to high humidity conditions results partial solvation of the film. 59
COLOR VARIATION it is caused by Improper mixing, uneven spray pattern and insufficient coating may results in color variation. The migration of soluble dyes, plasticizer and other additives gives the coating a mottled or spotted appearance. Remedies Use of lake dyes eliminates dye migration. Reformulation with different plasticizer and additives is the best way to solve film instability. 60
CRACKING Cracking occurs when internal stress in the film exceed the tensile strength of the film. The tensile strength of the film can be increased by using higher molecular weight polymers or polymer blends. Remedies • Adjusting the plasticizer type and concentration can minimi internal stress. • Adjusting the pigment types and concentration can minimiz internal stress 61
SPECIALIZED COATINGS : Electrostatic coating : it is efficient method for application of coating solution to conductive substrates. A strong electrostatic charge is applied to the substrate, Coating material containing opposite charged ions were sprayed on the charged substrate. Complete and uniform coating of corners is achieved. Vacuum film coating : It normally done in specially designed sealed baffled pan the pan is surrounded by a hot water jacket to dry the coated air is displaced inside with nitrogen to create vacuum environm Coating solution is applied by airless spray system. Vapors caused by pan can be removed by vacuum system. 62
Compression coating : It requires specialized coating equipment It characterized by two component system (tablet with in a tablet) or three component system (tablet with in a tablet with in tablet) Reasons If substrates are physically or chemically incompatible with each other If Substrate is sensitive to organic solvents or water Provide prolonged action , repeat action products. 63
COATING PARAMETERS : Rate of coating composition application = rate of evaporation of volatile solvents. Deviation from this equilibrium results in serious coating proble Mathematical modeling for aqueous automated coating proces Inlet A(T 1, H 1) +C 1 (S) +p. SA 1 A (T 2, H 2)+ C 2+Psa 2 exhaus AIR CAPACITY: quantity of water or solvent removed During coating process, it depends upon 1) quantity of air flow through tablet bed 2) Temperature of air 3) Water content of inlet air 64
COATING COMPOSITION : Inlet air provides heat to evaporate the water , the exhaust air Becomes cooler and contains water. Tablet surfaces are permeable to applied coating solution w Cause coating difficulties, so rapid removal of solvent is done Increase in temperature. TABLET SURFACE AREA : Size and presence of debossed feature affects the coating s The size of the atomized coating droplets must be smaller. 65
EQUIPMENT EFFICIENCY: Equipment efficiency = Net increase in coated tablet weig Total weight of non volatile coating applied to the tablets FACILITY & ANCILLARY EQUIPMENT: Facility require should meet to requirements of c. GMP. Adequate space is required for equipment , solution prepar and in- process storage. Safety requirements depending on nature of solvent, electrical explosion proofing, specialized ventilation. Exhaust air treatment to recover solvent or to prevent entry atmosphere. 66
CONCLUSION : By the usage of tablet coating process we may conclude that the following advantages : Mask the unpleasant taste & odour of the drug Provide protection to physical & chemical properties of drugs from enzymes, p. H, Better patient acceptance Bio availability of drug can be controlled 67
REFERENCES: LEON LACHMAN HERBERT A. LIEBERMAN ‘S Theory and practice of industrial pharmacy , special Indian edition 20 Pg no; 346 to 372. HERBERT A. LIBERMAN , LEON LACHMAN AND JOSEPH B SCHWARTZ’S Pharmaceutical dosage forms tabl Volume 3 , 2 nd edition revised and expanded , pg no 78 to 158 M. E. AULTON’S Pharmaceutics, the science of dosage form Design, 2 nd edition , pg no 441 to 448. 68
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