Tablet Coating Processes (PDF)

Tablet Coatings  Tablet coating is the application of a coating material to the exterior of a tablet with the intention of conferring benefits and properties to the dosage form over the uncoated variety  The rationales for tablet coating 1. To protect the drug from the env...

Tablet Coatings  Tablet coating is the application of a coating material to the exterior of a tablet with the intention of conferring benefits and properties to the dosage form over the uncoated variety  The rationales for tablet coating 1. To protect the drug from the environment 2. Masking of unpleasant testes 3. Making it easier to swallow 4. Improve product identity 5. Facilitate handling as it removes dust 6. Improves product appearance when there is noticeable d/f b/n batches 7. Reducing the risk of interaction between incompatible components 8. Increase product robustness as coated products generally are more resistant to mis -handling e.g. Abrasion and attrition 1 9. Modifying drug release 10/05/2024  Types of coating processes  Three main types are in use:  Film coating  Sugar coating  Press coating  Gelatin coating  Of these, film coating is the major technique:  almost all new coated products introduced on to the market are film coated 2 10/05/2024  Film Coating Film coatings add very little extra weight (up to approx. 5% increase) Various polymers (e.g. cellulose derivatives like HPMC) are used in film coating Ideal film polymers have  Good solubility  Low viscosity  Low permeability to water vapour  High mechanical strength 3 10/05/2024 The basic components of the coating formulation : Polymer  A film former capable of producing smooth thin films reproducible under the prescribed coating conditions  Solvent  Plasticizer  Affords flexibility and elasticity to the coat and thus provide durability. Examples; Polyethylene glycol (PEG)  Colorant  Provides an elegant appearance. Ex. Iron oxide pigment, Titanium dioxide  Miscellaneous - flavors, sweeteners, surfactants , antioxidants 4 10/05/2024  The coating Process 5 10/05/2024  Types of film coating 1- Immediate-release (non-functional) film coating:  They do not affect the biopharmaceutical properties of the tablet  They are readily soluble in water 2- Modified-release (functional) film coating:  They allow the drug to be delivered in a specific manner; i.e. they affect drug release behavior  Modified release film coatings are sub-classified into;  Delayed-release coating (enteric coating)  Extended-release coating 6 10/05/2024  Important parameters  Air capacity – how much humidity the air can hold  Coating composition  Tablet surface area- small tablets have a greater surface area per unit weight than big tablets  Equipment efficiency (e.g. coating pan dimensions and tablet movement through the process, how well/how fast the solvent can be pulled off)  If the coating rate is too slow for the conditions (high heat, fast air, big tablets)  then some of the coating will dry up before it actually coats 7 the tablets and it will be lost as dust 10/05/2024  Coating Equipments and coating Methods  Three methods a. Pan pour/Conventional coating pan/ I. Employs poring of solution II. The method is very slow & relies on the skill of the operator III. Tablets require additional drying to remove latent solvents IV. Not suitable for aqueous base solution because of localized over wetting is inherent  Problems:  Product erosion  Product instability due to unacceptable high latent moisture 8 10/05/2024 Mixing of tablet mass:  Pan shape and rotational speed and loading all affect the mixing of tablet mass  Uniform mixing is essential to depositing the same quantity of film on each tablet  Poor tablet movement in the coating pan may cause unacceptable color uniformity or affect the integrity of enteric film  Careful choice of equipment may ensure adequate mixing some tablet shape, and avoidance of chipping or breakage of tablets. 9 10/05/2024 Velocity of tablet pass under the spray affected by pan rotational speed  Too slow -> localized overwetting resulting in tablets sticking to each other or to the pan  Too high -> may not allow enough time for drying before reintroduced to the spray  thus a rough coating appearance on the tablets  Usually higher speed is used for non-aqueous film coating to prevent overwetting and  a lower speed for aqueous film coating to allow enough time for drying  Water dries more slowly than organic solvents 10 10/05/2024 11 10/05/2024  b. Pan spray Employs spraying of solution Spray patterns are selected to provide continuous band across the tablet bed Variables include 1. Pan Variables 1.  Pan design/baffling  Speed  Pan load  Pan speed 10-15 rpm for non aqueous coating  Pan speed 3-10 rpm to aqueous coating 12 10/05/2024  2. Process air  Air quality(dehumidification, seasonal adjustments)  Temperature  Air flow rate/ volume 3. Spray Variables  Spray rate  Degree of atomization  Spray pattern  Nozzle to bed distance  The degree of atomization and spray pattern depend on atomizing air pressure, air volume and shape and design of air jets in relation to the fluid stream 13 10/05/2024  Shape of the jets and pressure determine the droplet size  Pattern of spray and therefore amount of coating delivered is partly determined by jet positioning (wide, narrow)  Spray pattern is too wide -> application of coating directly to the pan surface resulting in wasted material and lower coating efficiency  Spray pattern is too narrow -> tablets need to make many more passes through the spraying area to be adequately coated resulting in a poor uniformity of coating or 14 localized overwetting 10/05/2024  Atomization: liquid stream is finely subdivided into droplets  Droplets too small some droplets dry before reaching the tablet bed  spray-drying effect results in roughness on the tablet surface  Droplets too large localized overwetting sticking, picking or rough "orange peel“ effect. 15 10/05/2024  c. Fluidized Bed Coating Process The tablet mass is fluidized (suspended in air) Ability to fluidize depends on: tablet shape, size, bulk density and quantity of load  Adequate fluidization and drying depend on: the volume and rate of the process air Control of the process air is achieved by: adjusting a variable speed blower  Airflow too high => tablet attrition and breakage  Airflow too low => tablets do not move fast enough through the spray region over wetting may occur (doesn’t dry right – rough surface results) 16 10/05/2024  Fluidization may also be affected by: increase in weight or by changes in the frictional characteristics of the tablets during coating application.  To maintain optimum fluidization: periodic adjustment of the rate and volume of air as the coating is applied and becomes thicker, adding to the tablet weight 17 10/05/2024 18 10/05/2024  Common film coating Defects, Causes and their Solutions N Defects Causes Solution o 1 Sticking & Over wetting or Decrease solution Picking excessive film application rate thickness Increase drying rate 2 Roughness Rapid drying of Moving spray nozzles solution before closer to the tablet reaching tablet bed bed 3 Orange peel effect Inadequate spreading Thinning the solution ( Bumpy or uneven of solution before surface) drying  Too high solution viscosity 4 Bridging Poor plasticizer Change plasticizer (Bridging of surface depression or breaking line) 19 10/05/2024 5 Filling(thick Too much solution Care full monitoring of film that the Solution fills bisect) application rate Thorough mixing of tablets 6 Blistering Common in oven drying Milder drying due to too rapid drying of the solvent form the core 7 Hazing/dull Too high processing Optimal drying film/bloom/ temperature used in temperature cellulosic polymers 8 color Improper mixing ,Uneven Use lake dyes variation spray  Insufficient coating  Migration of soluble dyes 9 cracking Internal coating stress in  Use high mwt polymers the film > the tensile to increase tensile strength of the film strength 20  Adjust stress 10/05/2024 in the film by adjusting the  Film evaluations  physical appearance  water vapor permeability  film tensile strength Major film coating problems or defects are due to: 1. Processing – e.g. not dry enough 2. Formulation – film cracking, bridging or break lines 21 10/05/2024  Sugar Coating  Sugar coating is the oldest method of tablet coating  It involves the successive application of sucrose- based solutions to tablet cores in suitable coating equipment  It is also the most complex, expensive, requires great expertise nearly an art, time-consuming, and increases the tablet weight significantly  Materials used in the sugar coating process include purified water, cellulose derivatives, polyvinyl, gums, & sugar  The advantage of sugar coating is the very smooth, high-quality surface it provides to the tablets 22 10/05/2024  Sugar coating is a multistage process and can be divided into the following steps: 1. Sealing of the tablet cores 2. Subcoating 3. Smoothing 4. Colouring 5. Polishing 6. Printing 23 10/05/2024  Sealing  Objective:  Applied to the tablet core for the purpose of separating tablet ingredients from water which is the major constituent of the coating formulation  Enhances product stability Material for sealing 12-20% shellac in alcohol  Disadvantage- impair bioavailability of tablets due to change in resin property  Solution-use shellac together with PVP 24 10/05/2024  Tablet porosity tends to absorb the first application of the solution  Therefore, one or more further application of the resin solution may be used Most sealing coat develops a degree of tack at some time during the drying process.  Hence, it is usual to apply a dusting powder to prevent tablets from sticking (Tackiness) e.g. pharmaceutical grade talc. 25 10/05/2024  Subcoating  Objective  To achieve spherical/round/ shape of tablet and remove tablet edges  It is a critical operation in sugar coating process that can have a marked effect on ultimate tablet quality  Large quantity of sugar-coatings are usually applied to the tablet core (typically increasing the tablet weight by 50-100%)  Much of this material build-up occurs during this stage and  is achieved by adding a bulking agent such as 26 Calcium carbonate, to the sucrose solution. 10/05/2024 Antiadherents e.g. Talc may be added after partial drying , to prevent sticking of the tablets together N.B. These procedures may be repeated till the desired shape and size are obtained How is that possible? Subcoating is achieved by the application of a gum based solution to the sealed tablet cores and followed by dusting powders. Purpose of dusting powder  Avoid tablet tackiness  Increase tablet build up to remove edge 27 10/05/2024  Sub-coating process 28 10/05/2024  Practical Sub-coating problems  Lumpy sub coat due to poor drying  Amount of dusting powder not matched with the amount of binder solution which will result in  Brittle coating  Dust accumulation in the back of the coating pan with consequent excessive roughness of tablet Remedy:  Application of a suspension sub coat formulation where the powder materials are dispersed in the gum-based solution  Allow solid build up to match with the binder solution 29 10/05/2024  Smoothing Objective  To make tablet surface more reflective resulting in a brighter, cleaner final core  Smoothing is accomplished by the application of a simple syrup solution (60-70%). 30 10/05/2024  Color Coating /finishing/  This is a critical to the successful production of sugar coating products and evolves multiple application of syrup solution containing appropriate coloring materials  Types of colorants  a. Dyes- water soluble  When used by a skilled operator produces the most elegant and brighter final color  Disadvantage  Migration of color mottling due to moisture  Remedy:  Apply small quantity of colored syrup and allow tablets to dry slowly  Each application should be allowed to dry thoroughly before subsequent application  31 It may require up to 60 applications 10/05/2024   Pigment- water insoluble  Advantage  No color migration  Forms thinner coats as the desired color is achieved more rapidly  Decrease processing time=> low cost of production  Easier to use by less skilled coating operators  Disadvantage  Incorporation to the syrup solution is difficult 32 10/05/2024  Polishing  Sugar coated tablets are naturally dull in appearance (frosted tablet) at the end of the coating process  Therefore, tablets need to be polished  Polishing agent  Bees wax  Carnuba wax  Hard parafine wax  A rough, irregular tablet will collect the polishing wax in the nooks and crannies of the tablet surface, resulting in a marbled appearance 33 10/05/2024  Printing  Different tablets could be identified by  manufacturer' logo, product name, dosage strength or other appropriate code  For sugar-coated tablets, such identification could be only achieved by printing process using special edible inks,. 34 10/05/2024 35 10/05/2024 Common Sugar coating problems, causes & their solutions No problems Causes solution 1 Tablet capping Soft tablets Optimize tablet High machine Optimize machine speed speed 2 Different range of Poor mixing Use baffling tablet size Optimize pan speed 3 Cracking or soft Excessive use of Optimize dusting, coating dusting solution volume and drying rate 4 Irregularities in Color migration Allow tablets to dry appearance slowly  Use pigments 36 10/05/2024  Compression Coating/Press Coating  Compaction of a dry coat around a tablet core, produced on the same tabletting machine  This type of coating avoids the use of solvents  It can be used to separate incompatible drugs in the same tablet, making a layered tablet. (ex. Robaxisal®)  Machinery for tabletting this way is complex and not widely used  Mechanically, it is a complex process, as the tablet may be tilted when transferred to the second die 37 cavity 10/05/2024 38 10/05/2024 39 10/05/2024  Gelatin-coated tablets  A recent innovation is the gelatin-coated tablets.  The innovator product, the gelcap, is a capsule shaped compressed tablet coated with gelatin layer Why? This allows the coated product to be about one-third smaller than a capsule filled with an equevalent amount of powder The gelatin coating facilitates swallowing Gelatin coated tablets are more tamper evident than 40 unsealed capsule. 10/05/2024 41 10/05/2024  Enteric coating  This technique is used to protect the tablet core from disintegration in the acid environment of the stomach for one or more of the following reasons: 1. Prevention of acid attack on active constituent unstable at low pH; 2. To protect the stomach from the irritant effect of certain drugs; 3. To facilitate absorption of a drug that is preferentially absorbed distal to the stomach 42 10/05/2024   The following polymers are among those commonly used for the purposes of enteric coating: 1. Cellulose acetate phthalate 2. Polyvinyl acetate phthalate 3. Suitable acrylic derivatives  Because they possess free carboxylic acid groups on the polymer backbone, they exhibit a differential pH solubility profile  They are almost insoluble in aqueous media at low pH, but as the pH rises they experience a sharp, well denned increase in solubility at a specific pH,  e.g. pH 5.2 for cellulose acetate phthalate 43 10/05/2024  Evaluations of coated tablets  Adhesion tests with tensile-strength testers  Diametric crushing strength of coated tablets with tablet hardness tester  Disintegration and/or dissolution  Stability studies  Visual inspection of film surface roughness, hardness, and color uniformity  Resistance to abrasion 44 10/05/2024