Sugar coating involves many steps hence it requires experience, and in some cases elaborate equipment. Though the stages differ from one manufacturer to another, a typical sugar-coating process involves the following steps:. Read more on sugar coating of pharmaceutical tablets. Film coating involves the deposition of a thin layer of film-forming polymeric material on the tablet core. The process was introduced in the s as improvement on the traditionally sugar-coating process.
Film coating has proved successful as a result of the many advantages offered, including:. Film coating can also be used to coat other formulations including capsules, beads, granules, drug powders, and crystals. A spray-atomization technique is more commonly utilized.
Read more on film coating of pharmaceutical tablets. Compression coating also referred to as press coating or dry coating is the process by which a fine dry granulation is compressed onto a tablet core of drug.
This is usually achieved using a specially designed tablet press such as Drycota Manesty and Prescota Killian. Compression coating is essentially a dry process and thus may be suitable for coating tablets containing heat and moisture liable drug s such as aspirin and penicillins.
This coating process has also been used to separate two incompatible active pharmaceutical ingredients; one contained in the tablet core and the other in the coating. Repeat action and sustained action tablets are produced by this coating method. ICH guidelines also prefer the avoidance of organic solvents in pharmaceutical dosage formulations considering products safety profile. This review discusses the basic concepts of tablet coating, the recent advancements made, the problem faced during the process, their solutions and coating evaluation.
Tablet coating can be described as a process of applying an edible paint on the surface of a pharmaceutical dosage form to achieve specific benefits. This is an additional process in tableting which causes an increase in the cost of tablet production. Coating can be applied to several kinds of solid dosage forms like tablets, pellets, pills, drug crystals, etc. When a coating solution is applied to a batch of tablets in a coating pan, the surfaces of the tablets get covered with a tacky polymeric film.
The tablets are then allowed to dry and the film eventually forms a non-sticky dry surface. The coating technique involves parameters such as the spray pattern, drop size, and nozzle spacing in addition to multiple other non-spray related parameters which must all be precisely controlled in order to ensure uniform distribution of the coating material [1, 2].
It is most desirable that the coating should be uniform and should not crack under stress. Hence, various techniques were designed for the application of the coating on the tablet surface. Generally, the coating solutions are sprayed onto the uncoated tablets as the tablets are being agitated in a pan, fluid bed, etc. As the solution is being applied, a thin film is formed which sticks to each tablet.
The liquid portion of the coating solution is then evaporated by passing air over the surface of the tumbling pans. The coating may be formed either by a single application or may be developed in layers through the use of multiple spraying cycles.
Rotating coating pans are often used in the pharmaceutical industry. Tablet coating developed originally from the use of sugar to mask the taste and provide an attractive appearance to at the core. The process of tablet coating consists of several steps, which are described below:. A seal coat is applied over the tablet to prevent moisture penetration into the tablet core. Shellac was previously used as a sealant. But due to polymerization problems, it was replaced by zein a corn protein derivative.
The imperfections in tablet surface are covered up and the predetermined size is achieved. This step requires the maximum skill. As the sugar coating process is very time consuming and is dependent on the skills of the coating operator, this technique has been replaced by film coating technology. The process involves spraying of a solution of polymer, pigments and plasticizer onto a rotating tablet bed to form a thin, uniform film on the tablet surface.
An ideal film coating material should possess the following characteristics [2]:. Currently, the most common technology for coating solid dosage forms is the liquid coating technology aqueous based organic based polymer solutions.
A small cylindrical insert helps the tablets to move upwards while being exposed to spray mist in the centre of the drum. Tablet coating is a very important aspect of the manufacture of commercial tablets.
Many parameters, technical terms and key phrases are used by practitioners. The following list is provided as a helpful guide for the newcomer to this area. Air Capacity — this parameter denotes the water quantity or the solvent that is removed during the coating process.
It depends on the air quantity that is flowing through the bed, air temperature and the water quantity that the inlet air contains. Tablet Surface Area — plays an important part in the uniform coating of the tablet.
The total area for the unit decreases considerably depending on the size of the tablet. Film application of the same thickness needs less coating. During the coating process only a part of the total surface is coated. The continuous partial coating and recycling will eventually result in the tablet to be fully coated. Equipment Efficiency — coating efficiency is achieved by dividing the net increase in the weight by the total of the nonvolatile coating applied to the tablet.
The important difference in coating efficiency between the film and the sugar depends on the amount of coating material that collects on the wall. The sugar coating process involves several steps including — sealing, color coating, subcoating and printing. Latest techniques make use of spray system and automation to increase coating efficiency and uniformity of the end product.
The base formula makes use of old formulas and then modified to adapt to the current requirement. Common alterations include the ratio of polymer and plasticizer. Materials used include film formers, solvents, colourants, plasticizer, opaquant-extenders, anti-oxidant and even surfactant.
The quality of the film can be modified by using plasticizers such as PG, low molecular weight PEG, castor oil, spans and glycerins. The spans and castor oil is used for organic solvent based solution whereas the PEG and PE are for aqueous coating solution. Lakes are preferred as they show viable results. Since colourants are expensive and a high concentration amount is needed, other materials are used such as silicates, carbonates and titanium dioxides are to increase the tablet coverage and as well as give the tablet a pastel color look.
The enteric coating is used to protect the core of the tablet from disintegrating when exposed to the stomach acid, prevent acid sensitive API degradation, and stomach irritation, delivery of the API to the intestine tract and to provide a timed release of the components.
There are 2 kinds of layering - 1 layer and 2 layer system. The sealing coat is altered by adding one of the enteric polymers in sufficient number in order for it to pass the enteric test for dissolution.
The sub-coating and succeeding coating steps are for conventional sugar coating. The enteric polymer has the ability to form a direct film during the film coating process. Sufficient weight must be used in order to have an efficient enteric effect. The enteric coating can be mixed with other compounds such as polysaccharides which can dissolve in the colon. Language English. Coating methods There are two principal methods of coating tablet: sugar coating and film coating.
Four processes are commonly employed in sugar coating, in the following order: Sealing Water proofing — sealing involves hardening the external surface of the tablet by providing a moisture barrier. Colouring — provides the tablet the appropriate colour for the end product. The processes are summarised below.
Sealing Water Proofing Before any sugar or syrup is added to the tablet, the core must be sealed and thoroughly dried so that it is free from any moisture or residual solvents. Sealants that are commonly used include: Shellac Zinc oxide Cellulose acetate phthalate Polyvinylacetate phthalate Hyroxylpropylcellulose Hyroxypropylmethylcellulose Subcoating The sugar coating process actually starts with a subcoating stage in which the sides of the tablet are rounded or shaped up to the desired appearance.
There are two ways of Subcoating: A gum based solution or syrup is coated on the tablet, followed by the application of a suitable powder filler. Colour Coating Colour coating is the most crucial penultimate stage in the coating process as multiple sugar solution is added to ensure that the predetermined colour is achieved. Polishing The final step in the sugar coating process is a polishing step.
Film Coating Requirements The basic requirements for film coating need to be considered independently of the actual equipment being used. Developing the Coating Formulation The following questions should first be answered in order to determine if film coating is applicable: Is it important to mask the taste, odour or colour of the tablet?
Is it important to control the release of the drug? What are the specifications that need to be fulfilled during the developmental stage? Formula Optimization The base formula for every coating is usually achieved taking a previous formula and modifying it to improve the bond of the coating with the core of the tablet, increasing the hardness of the coating etc.
Povidone Povidone is available in 4 viscosity levels: K, K, K and K corresponding to average molecular weight of the polymer of 10,, 40,, , and , respectively. Sodium Carboxy Methyl Cellulose This agent is only useful when dispersed in water in order to form colloidal solutions so is not the right choice as a coating for tablets that are based on organic solvents. Acrylate polymers Acrylate polymers are marketed under the EudragitO as a cationic polymer.
Solvents Solvents are used to dissolve the polymers and other additives ready for spraying or otherwise coating the surface of the tablet or capsule. The basic solvent requirements are: It should be able to dissolve or disperse the polymer It should easily dissolve other additives added to the system Small concentrations of the polymer should not cause any problems for exceedingly viscous solution It should be non-toxic and non-flammable It should be odourless, colourless and tasteless It should not cause any environmental problems Have high drying rate Most of the solvents used are by themselves, however some are combined with other solvents.
Plasticizers Once the solvents are removed, the polymers tend to stick together creating a 3D honeycomb look. Colourants Most colourants used in film coating are available in solution or suspension form.
Opaquant-Extenders These extenders are fine inorganic powder used to increase the fill coverage and provide more pastel colour shade to the tablet.
Common inorganic powders include: Titanium dioxide Silicates aluminum silicates including talc Carbonates e. Other Components Other solutions that can be added to coating formulations include surfactants, flavours, antimicrobials, antioxidant and sweeteners. Enteric Coating Enteric coating is a term used to describe the coating that gives complete protection to the core of the tablet. The following should be noted: The applied coating should either prevent drug release or the ingress of gastric fluids under specified conditions of pH and also promote rapid release of the drug in the higher pH regions of the jejunum, duodenum etc.
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Many solid pharmaceutical dosage mediums are produced with coatings Either on the external surface of tablets, or on materials dispensed within gelatine capsules. Coating serves a number of purposes: Protects the tablet or the capsule contents from stomach acids Protects the stomach lining from aggressive drugs such as enteric coated aspirin Provides a delayed release of the medication Helps maintain the shape of the tablet Ideally, the tablet should release the material gradually and the drug should be available for digestion beyond the stomach.
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