![]() The use of inadequate dusting powders increases the risk of sticking and twinning, whereas its excessive use can create tablets that have brittle coatings. While this method has proved to be very effective, particularly where there is difficulty in covering edges, it is important to ensure that a careful balance is achieved between the relative amounts of gum solution and dusting powders used. This process of application of gum solution, spreading, dusting, and drying is repeated until a satisfactory coating is achieved. Once this solution has been distributed uniformly throughout the tablet mass, it is followed by a liberal dusting of powder (which serves to reduce tack and facilitate tablet buildup) and drying. The lamination process is perhaps the older of the two techniques used, and involves application of a “glue” (in the form of an aqueous solution of a suitable gum, such as gum acacia, or even gelatin) in quite substantial quantities to the sealed tablet cores. There are two techniques for the subcoating application lamination process and suspension subcoating process each with its distinct features and advantages. It also provides the foundation for smoothing and color coating with any weakness in the final sugar coat often being attributable to weaknesses in the subcoat. Subcoating provides the rapid buildup necessary to round up the tablet edge. It involves the application of large quantities of sugar-coatings to the tablet core, significantly increasing the tablet weight by 50 – 100 %. This step is regarded as the first major step in sugar-coating process. ![]() If the final product is to have enteric properties, this result can be achieved using one of the enteric polymers (such as PVAP or CAP) as the basis for the seal coat and ensuring that sufficient coating material is applied. This problem can be minimized either by incorporating small amount of PVP into the shellac-based seal coat formulation or by using one of the other more stable polymers (such as PVAP). While use of shellac has been universal, this natural polymer can undergo further polymerization on storage, causing the seal coat to become completely insoluble to the point where bioavailability of the active drug substance may be compromised. If there is a tendency for either of these problems to occur, one solution is to replace part or all of the talc with some other material such as terra alba, which will form a slightly rougher surface.Ĭommon materials used as sealants include shellac, zein, hydroxypropyl methylcellulose (HPMC), cellulose acetate phthalate (CAP), or polyvinyl acetate phthalate (PVAP). Such poor wetting often results in uneven subcoat buildup, particularly on the tablet edges. Hence, one or more further application of resin solution may be required to ensure that the tablet cores are properly sealed.īecause most sealing coats develop a degree of tack (stickiness) at some time during the drying process, detackifiers, such as asbestos-free talc, are often used to minimize the risk of “twinning” or clumping.Įxcessive use of talc may cause problems, firstly, by imparting a high degree of slip to the tablets, thus preventing them from rolling properly in the pan, and secondly by creating a surface that, at the beginning of the subsequent subcoating stage, is very difficult to wet. Another variable is tablet porosity because highly porous tablets will tend to soak up the first application of solution, thus preventing it from spreading uniformly across the surface of every tablet in the batch. The quantities of material applied as a sealing coat will depend primarily on tablet and batch size. Warm air is then blown into the pan during the coating to hasten the drying and to prevent tablets from sticking together. In a manual seal-coating operation, the sealant which usually consist of alcoholic solutions of resins (approximately 10–30% solids) is evenly and gently poured or sprayed over the tumbling tablet bed (preheated to 40 oC). oils, acids, etc.) from migrating to the tablet surface and spoiling the appearance. Sealing also prevents certain types of materials (e.g. It is an optional step but is usually required to prevent the tablet core and its contents from absorbing water, softening, and initiating disintegration during the subsequent steps of the sugar-coating process. ![]() Seal coating involves the application of specialized polymer-based coating (either by ladle or spray techniques) directly to the tablet core. Sealing of the tablet core (Waterproofing/ Protective coating) ![]() Sealing of the tablet core (Waterproofing/ Protective coating)ġ. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |