Pharmaceutics III (PT 506) Lecture 9: Tablet Coating - Lecture Notes PDF

Pharmaceutics III (PT 506) SOLID DOSAGE FORMS Tablet (4) LECTURE 9 By Maha Mostafa ghalwash Department of Pharmaceutics &Drug Manufacturing 1  Tablet Coating ❑ Tablet coating is the process where coating material is applied to the surface of the ta...

Pharmaceutics III (PT 506) SOLID DOSAGE FORMS Tablet (4) LECTURE 9 By Maha Mostafa ghalwash Department of Pharmaceutics &Drug Manufacturing 1  Tablet Coating ❑ Tablet coating is the process where coating material is applied to the surface of the tablet to achieve the desired properties of dosage form over the uncoated variety ❑ Tablet coating is additional step that increase cost, so the decision to do it depend on different reasons. 2 Causes of tablet coating:- 1) To protect the drug from degradation in the stomach (formulate as controlled release coating, enteric coating). 2) To prevent drug-induced irritation at a specific sit within G.I.T e.g. anti-inflammatory drugs. 3) To target the drug release to a specific site. 4) To mask the Taste of the drug. 5) To improve the appearance of the tablet 6) To assist tablet movement and mobility specially for patient with dysphagia while swallowing. 7) Improve stability of the tablet 3 Types of tablet Coating 4 Tablet Properties Coating compositions Coating process Ideal Tablet Shape for Non-Enteric Coating Process Coating coating Materials Equipment Tablet physical Enteric Coating Coating Process properties Materials Solvents Sugar Coating Plasticizer Film Coating Colorants Special Coating Opaquenats Evaluation of Film and Film defects 5  A-Tablet properties ❑ Tablet must be strong enough possess the proper physical characteristics, to withstand the intense mechanical stress that results from striking ❑ (Other tablets and The walls of coating machine). ❑ Tablet shape intactness is another property. Film coatings will adhere to all exposed surfaces. Hence the imperfection will be coated and not eliminated. 6 ❑ Tablet surface that are brittle, that soften in the presence of heat, or that are affected by the coating compositions tend to become rough in the early phase of the coating process and are unacceptable for film coating ❑ The physical shape of the tablet is important. Coating include covering tablet with a sticky polymeric material that before become completely dry will form sticky semisolid and eventually to a non sticky dry surface. So, tablet need a constant movement inside the coating machine or tablet agglomeration can occur. 7 ❑ The ideal tablet shape for coating is sphere which allows tablet to roll freely in the coating pan with minimal tablet-to-tablet contact. ❑ The worst shape is a square flat-faced tablet in which coating materials would collet between the surfaces to glue them together. That’s why coated tablets usually have round surfaces.??? ❑ Tablet surface hydrophobicity / hydrophilicity should match that for the coating materials. ❑ Coating materials must wet the tablet surface. For this reason, surfactant may be added to the coating solution 8  Main steps of tablet coating 1- The tablets are placed within the coating apparatus and agitated. 2- The coating solution is sprayed on the surface of the tablets. 3- Warm air is passed over the tablets to facilitate removal of the solvent from the adsorbed layer of coating solution on the tablet surface. 4- When the solvent is completely evaporated, the tablet will be coated with the solid components of the coating solution. 9 1- Coating Formation: The coating materials (Polymers or sugar) + the coating solvent and other excipients required to improve the formation. Such as colourants, opacifiers, plasticizers. 2- Coating Emulsions: They are more recently developed, in which the polymer is dissolved in a volatile organic phase with the colourants and opacifiers; plasticizer is emulsified within the external aqueous phase. 10  Coating materials should have the following properties: 1. Soluble in solvent for coating preparation. 2. Able to produce elegant looking product. 3. Stability in the presence of heat, light, moisture, air and the substrate being coated. 4. Film properties should not change with aging. 5. Essentially no taste, odor. 6. Compatibility with common coating solution additives. 7. Nontoxic and pharmacologically inert. 8. Should not tend to fill of the debossed tablet surfaces. 9. Have resistance to cracking. 11  B- Coating Compositions Polymers used to form the film around the tablet. Non-Enteric Materials: these materials tend to solubilize inside the GI tract and release the drug. Hydroxypropyl methylcellulose (HPMC). Ethyl Cellulose (EC). Enteric Materials: these materials change to solubilize depending on pH of the GI tract. Methyl Cellulose Phthalate (MCP). Cellulose Acetate Phthalate. Acrylate Polymers. 12 Properties of ideal enteric coating material:- 1) Resistance to gastric fluids. 2) Ready susceptibility or permeability to intestinal fluids. 3) Compatibility with the most coating solution component and the drug substrates. 4) Stability alone and in coating solutions. 5) Formation of a continuous (uninterrupted) film. 6) Nontoxicity. 7) Reasonable cost. 8) Ease of application without specialized equipment. 13 ❑ Film-coated tablets disintegrate within 30 minutes and other coated tablets disintegrate within 60 minutes. ❑ All enteric coated tablets must pass USP disintegration test where the tablet disintegrate within 2 hrs (for most tablet). ❑ Passing disintegration test does not mean guarantee optimal bioavailability. 14  Several challenges will face enteric coated tablet inside the body 1) The pH of stomach varies from 1-5. Some patients are having achlorhydria or hypochlorhydria. 2) The amounts of gastric fluids may vary between individual; and for same individual from time to time. 3) Gastric residence time will vary from 30 min to more than 4 hrs depending on the time of its administration whether it was consumed with food and the type and quality of food, and patient physiological factors. 15 4) USP test does not require to test drug amount in solution during disintegration test. In some cased drug can escape before tablet breakage so tablet will pass USP test but will fail to protect GI tract. 5) Some enteric coated techniques uses retardant polymer which depend on hydrophobicity and not pH dependent (example Polyethylene Oxide). In this case polymer needs time to solubilize and allow drug to release so if the tablet travels so fast in the GI tract it may not have enough time to solubilize, and tablet will fail to release their contents. 16  solvent Used to dissolve or disperse polymer and other additives. The most widely used solvents (alone or in combination) are :- Water Ethanol Chloroform Acetone. 17 Consideration for ideal solvent:- 1) It should easily disperse other coating solution components into the solvent system. 2) Small conc. of polymers (2 to 10 %) should not result in an extremely viscous solution, which will create coating problems. 3) It should be colorless, tasteless, odorless, inexpensive, non- toxic, inert and nonflammable. 4) It should have rapid drying rate. 5) It should have no environmental impact. 18  Aplasticizer ❑ a non-volatile material which when incorporated with the film former, improves the flexibility and adhesion properties of the resulting coating film. ❑ Without a plasticizer, most of the polymers tend to pack together in a rigid three-dimensional arrangements. ❑ A combination of plasticizers may be needed to achieve the desired effect. 19 Factors affecting the conc. Of the plasticizer(s) used:- ❖ The polymer type. ❖ Method of application. The amount and type of plasticizers to be used for any given polymer can be based on the polymer manufacturer's recommendations. Recommended levels of plasticizers can range from 1-50% w/w of the film former. Some of the commonly used plasticizers are ✓ castor oil, glycerin,l ow molecularweight polyethylene glycol (PEG) (200-400 series),, Tweens and Spans. In aqueous coating, water-soluble plasticizers, e.g., PEG are used. Conversely, castor oil and Spans are used primarily for organic coating 20 solutions.  Opaquants ❑ These are very fine inorganic powders used in the coating solutions to provide more pastel colors and increase film coverage. ❑ These opaquants are used to: ✓ Provide a white coating or ✓ Mask the color of the tablet core. ❑ Colorants are much more expensive than these materials and less colorant is required when opaquants are used. ❑ The most commonly used material for this purpose is Titanium Dioxide. 21  C-Coating process: ❖ The initial stage in the coating process involves the deposition and subsequent spreading of the atomized coating solution or emulsion. On the tablet surface, then an initial film formation on the Surface of the table. ❖ As drying continuing. The saturation solubility of the cooking mater in the solvent is exceeded and the solid coating is formed on the tablet surface. 22  Sugar Coating ❑ Sugar coating involves several steps, the duration of which ranges from few hours to several days. ❑ A successful product greatly depends on the skill of the operator. ❑ This is especially true in the pan-ladling method in which the coating solution is poured over the tablets. The operator determines the Quantity of solution to be added, The rate of pouring, When to apply the drying air and How fast the tablets should be rotated in the pan. 23 Sugar coting process involves the following steps: 1) Sealing, 2) Sub coating, 3) Syruping (smoothing), 4) Finishing and polishing 24 1) Sealing: To prevent moisture penetration into the tablet core, a sealing coat is applied. This is especially needed in pan ladling processes, in which localized over wetting of a portion of the tablets occurs. Without a sealing coat, the overwetted tablets would absorb excess moisture, leading to tablet softening or disintegration and affecting the physical and chemical stability of the finished product. 25  The sub-coating It is applied to round the edges and build up the tablet size. Sugar coating can increase the tablet weight by 50-100%. The sub-coating step consists of applying a sticky binder solution (e.G. Gelatin or sugar solution) to the tablets followed by a dusting of a powder (e.x. Talc powder) and then drying. Subsequent sub-coats are applied in the same manner until the desired thickness is achieved. 26  For spray processes, a sub-coating suspension containing both the binder and the dusting powder is sprayed intermittently on the tablets. Any coat should not be applied unless the previous one is completely dry. 27  Syruping (Smoothing/Coloring) ❑ purpose of this step is to:- ❖ Hide the imperfections in the tablet surface caused by the sub- coating step. ❖ To impart the desired color to the tablet. ❑ This step perhaps requires the most skill. ❑ The syruping coat may contain powder (e.g. calcium carbonate). ❑ Dilute colorants can be added in this step to provide a tinted color that facilitates uniform coloring in the later steps. 28  Colorants In general, no color is added until the tablets are quite smooth; premature application to rough tablets can produce a mottled appearance in the final tablets. In the subsequent syruping steps, syrup solutions containing the dye are applied until the final color is achieved. 29  Finishing and polishing Finishing: in the finishing step, a few clear coats of syrup may be applied. Polishing: the desired luster (gloss) is obtained in this step. The tablets can be polished in clean coating pans by using certain wax (e.g. beeswax). 30  Film Coating Process It is more preferred than sugar coating because it is ❑ Faster, ❑ More economic, ❑ Versatility of film forming polymers that can be used and ❑ It does not increase the final tablet weight greatly (only 2-5%). 31 Compressed coating The coating requires a specialized tablet press machine. This type of coating is not popular but has some advantages 1. to mask the taste 2. protect the core from organic solvent or water. 3. delaying the enteric properties and 4. preventing the separation of the incompatible ingredients. 32 Electrostatic coating ❑ coats are applied to the electrically conductive substrates. ❑ A strong electrostatic charge is applied to the substrate. ❑ The materials in the coating process contain ionic species that are of opposite charge which are then sprayed onto the charged substrate. ❑ The method is limited to substances and spraying solutions that can be electrically charged 33 Dip coating the tablet’s core is simply dipped into the coating liquid. the tablets are then placed in a traditional coating pan to dry. The steps are repeated until the desired coating is achieved. Disadvantages the lack of versatility, low speed as well as low reliability compared with the spraying methods. Although specialized equipment has been developed for dip coating, no commercial application for it has been attained. 34 Vacuum film coating ❑ This procedure uses a specially designed baffled pan/drum, whereby the pan is heated by a hot water jacket and sealed so that it can be evacuated. ❑ Tablets are then placed in the pan and the air in the pan/drum is displaced by nitrogen before it is evacuated to a desired level of vacuum., ❑ The coating solution is applied to the tablets via an airless spray system. Evaporation of the water from the sprayed film is driven by the heated pan whereas organic vapors are removed via the vacuum system. ❑ As there is no high velocity heated air for drying the product, the energy required by vacuum film coating is low and the coating efficiency is higher. ❑ Organic better than aqueous solvents are effective and ideal for the vacuum film coating system as there are minimal safety and environmental concerns. 35  Coating Equipment 1. Conventional pan system 2. Perforated pan system 3. Fluidized bed (air suspension) system 36  Conventional Pan System IT consists of a spherical pan mounted angularly on a stand. The pan is rotated by a motor. Heated air is directed into the tablet bed and is exhausted by means of ducts. The coating materials (solution) are applied to the tablets by either ladling or spraying on the rotating tablets. Using of spraying is more preferred because it is faster, distribute the coating materials more evenly and reduce the drying time. 37  Perforated Pan System It is the most widely used machine in tablet coating. It consists of a perforated drum that rotates in a closed chamber. Drying air is passed through the tablets and is exhausted through perforations in the drum. Perforated pan coaters are efficient with high coating capacity and can be automated completely for both sugar and film coating process. 38  Fluidized Bed (Air Suspension) System ❖ It is also highly efficient coating system. ❖ Fluidization of tablets is achieved in columnar chamber by upward flow of the drying air. ❖ The air flow is controlled so that the air stream enters the column causing the tablets to rise in the center, then they fall toward the chamber walls and move downward to re- enter the air stream at the bottom of the chamber. ❖ The coating solution is continuously applied from a spray nozzle located on the top or bottom of the chamber 39 40  Coating Problems 1. Picking and sticking. This occurs when the coating removes a piece of the tablet from the core. It is caused due to over-wetting the tablets, under-drying, or poor tablet quality. This can be treated by continuous addition of material to give uniform film. 41 2. Bridging. A bridge is formed by peeling of the film over the writing symbols or logo. it is caused due to: ❑ Improper application of the solution, ❑ Poor design of the tablet embossing, ❑ High coating solution viscosity, or ❑ Improper atomization pressure. ❑ inadequate plasticizer This treated by using 1) wetting agent to decrease viscosity, 2) diluted solution of polymer and 3) use effective plasticizer 42 3. Capping. This occurs when the tablet separates in laminar fashion. The problem occurs due improper tablet compression, but it may not reveal itself until you start coating. Be careful not to over- dry the tablets in the preheating stage, that can make the tablets brittle and promote capping. 4. Twinning. This is the term for two tablets that stick together, and it’s a common problem with capsule shaped tablets(oblong), you can solve this problem by balancing the pan speed and spray rate. 43 5. Mottled color. No uniform distribution of the color and its migration. This can happen when: 1. The coating solution is improperly prepared, 2. The actual spray rate differs from the target rate, 3. The tablet cores are cold, or 4. The drying rate is out of specification. ❑ The tablet become too soft and/or ❑ the coating process was too wet. 44 6. Orange peel (roughness). This refers to a coating texture that resembles the surface of an orange. It is usually the result of combination 1. High atomization pressure with 2. Spray rates that are too high. This can be treated by regulating the rate of atomization pressure and spray speed. 45 7- Tablet Discoloration caused by interactions of ingredients in the core or by heat from the process causing ingredients in the core to migrate through the coating. Problem is commonly seen with nutraceutical products. it is caused due to:- Spray coating solids are too low, allowing moisture to penetrate the core during application of the coating. Product is not receiving enough protection from moisture during storage. This treated by using:- select a film coating system ❑ Capable of being sprayed at higher solids. ❑ Capable of environmental moisture protection. 46 47