what are the various steps involved in sugar coating?

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Sugar coating Compressed tablets may be coated with coloured or uncoloured sugar layer. The coating is water soluble and quickly dissolves after swallowing. The sugarcoat protects the enclosed drug from the environment and provides a barrier to objectionable taste or order. The sugar coat also enhances the appearance of the compressed tablet and permit imprinting manufacturing's information. Sugar coating provides a combination of insulation, taste masking, smoothing the tablet core, colouring and modified release. The disadvantages of sugar coating are the time and expertise required in the coating process and thus increases size, weight and shipping costs. Sugar coating process involves five separate operations: I. Sealing/Water proofing: provides a moisture barrier and harden the tablet surface. II. Subcoating: causes a rapid buildup to round off the tablet edges. III. Grossing/Smoothing: smoothes out the subcoated surface and increases the tablet size to predetermine dimension. IV. Colouring: gives the tablet its colour and finished size. V. Polishing: produces the characteristics gloss. Sealing/Water proofing Prior to applying any sugar/water syrup, the tablet cores must be sealed, thoroughly dried and free of all residual solvents. The seal coat provides a moisture barrier and hardness the surface of the tablet in order to minimize attritional effects. Core tablets having very rapid disintegration rates conceivably could start the disintegration process during the initial phase of sugar coating. The sealants are generally water-insoluble polymers/film formers applied from an organic solvent solution. The quantities of material applied as a sealing coat will depend primarily on the tablet porosity, since 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. Hence, one or more further application of resin solution may be required to ensure that the tablet cores are sealed effectively. Common materials used as a sealant include Shellac, Zine, Cellulose acetate phthalate (CAP), Polyvinylacetate phthalate, Hyroxylpropylcellulose, Hyroxypropylmethylcellulose etc. Subcoating Subcoating is the actual start of the sugar coating process and provides the rapid buildup necessary to round up the tablet edge. It also acts as the foundation for the smoothing and colour coats. Generally two methods are used for subcoating: i)The application of gum based solution followed by dusting with powder and then drying. This routine is repeated until the desired shape is achieved. ii)The application of a suspension of dry powder in gum/sucrose solution followed by drying. Thus subcoating is a sandwich of alternate layer of gum and powder. It is necessary to remove the bulk o the water after each application of coating syrup. TABLE.23. TYPICAL BINDER SOLUTION FORMULATION FOR SUBCOATING(1) %W/W %W/W Gelatin 6 3.3 Gum acacia (powdered) 8 8.7 Sucrose (powdered) 45 55.3 Distilled water to 100 to 100 TABLE.24. TYPICAL DUSTING POWDER FORMULATION FOR SUBCOATING(1) %W/W %W/W Calcium carbonate 40.0 - Titanium dioxide 5.0 1.0 Talc, asbestos free 25.0 61.0 Sucrose( powdered ) 28.0 38.6 Gum acacia (powdered) 2.0 - TABLE.25. TYPICAL SUSPENSION SUBCOATING FORMULATION(1) %W/W Sucrose 40.0 Calcium carbonate 20.0 Talc, asbestos free 12.0 Gum acacia(powdered) 2.0 Titanium dioxide 1.0 Distilled water 25.0 Grossing/ smoothing The grossing/smoothing process is specifically for smoothing and filing the irregularity on the surface generated during subcoating. It also increases the tablet size to a predetermined dimension. If the subcoating is rough with high amount of irregularities then the use of grossing syrup containing suspended solids will provide more rapid buildup and better filling qualities. Smoothing usually can be accomplished by the application of a simple syrup solution (approximately 60-70 % sugar solid). This syrup generally contains pigments, starch, gelatin, acacia or opacifier if required. Small quantities of colour suspension can be applied to impart a tint of the desired colour when there are irregularities in coating. Colour coating This stage is often critical in the successful completion of a sugar coating process and involves the multiple application of syrup solution (60-70 % sugar solid) containing the requisite colouring matter. Mainly soluble dyes were used in the sugar coating to achieve the desired colour, since the soluble dye will migrate to the surface during drying. But now a days the insoluble certified lakes have virtually replaced the soluble dyes in pharmaceutical tablet coating. The most efficient process for colour coating involves the use of a predispersed opacified lake suspension. Polishing Sugar-coated tablets needs to be polished to achieve a final elegance. Polishing is achieved by applying the mixture of waxes like beeswax, carnubawax, candelila wax or hard paraffin wax to tablets in polishing pan.
ROHAN DESHPANDE JSS college of pharmacy, Mysore-5700 15.

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