Various coating defects observed in case of ayurvedic tablets are tablet breakage moisture pickup poor ohysical appearance Herbal ingredients have poor compressibility and compressed tablets are generally not very strong, such tablets tend to generate lots of powder during initial stages of film coating, making the tablet surface very rough,this powder interferes with the colour of the film coating, giving it a different colour shade than the desired one. The thermal expansion of the herbal ingredients is very different then the values for other excipients used for tablet manufacturing. As the tablets are exposed to high temperature during film coating, the difference in these values create serious problems in retaining the tablet surface smoothness during coating. If the difference in these values is very high, the core tablet may expand so much to rapture the film coating. Reference: http://www.expresspharmaonline.com/20061215/ipcspecial08.shtml

If the rate of drying increases the defects observed are peeling,film cracking. If the rate of drying decreases the defects observed are twinning,logo bridging,picking&sticking. If the pan speed increases the defects observed are surface erosion,edge erosion. If the pan speed decreases the defects observed are twinning,picking&sticking. If the viscosity of coating solution is low the defects observed are orange peel,edge erosion,film cracking. N.balaji

Orange peel: Appears as a roughened film due to spray drying. This condition relates to the level of evaporation that occurs as the spray droplets travel from the gun to the tablet bed. If there is excessive evaporation, the droplets do not have the ability to spread and form a smooth coating. A narrow droplet size distribution is important to ensure that the majority of droplets dry at the same rate. Remedies: Excessive evaporative rate Reduce the inlet and exhaust air temperatures Reduce the gun-to-bed distance Excessive atomization of the spray Reduce the nozzle air pressure Large droplet size variation Reduce the solution viscosity Reference: 1.N.K.Jain, pharmaceutical product development. New Delhi.OBS publishers,2006.93.print. N.balaji

hi vijay Twinning: Twinning is a form of overwetting whereby two or more of the tablet cores are stuck together. May be due to any of the possible causes for overwetting Remedy: Poor tablet core design- Change tablet design to eliminate large flat surfaces Reference: 1.N.K.Jain, pharmaceutical product development. New Delhi.OBS publishers,2006.93.print. n.balaji

hi suhaas If the pan is under loaded to the point that tablets do not cover the exhaust plenum, drying efficiency will be severely reduced as most of the drying air will take the low resistance path directly to exhaust rather than passing through the tablet bed. Simplistic thinking would suggest that a partial pan load would result in a fast process. The reverse is actually true - under loaded pans result in longer coating times. Geometric similarity means that the shape and dimensions of the pan coater are proportional across various scales and can be achieved by having systems with similar aspect ratios (ratio of pan length to diameter). Equipment manufacturers need to ensure that the aspect ratio of pans across scales is constant. The height, width, and shape of passive baffles should also be proportional across the different scales in order to achieve similar mixing. The geometric similarity can further be achieved by keeping the pan load to pan volume ratio constant. This in turn keeps the h/D ratio constant, where h is the closest distance from the center point of the pan to the bed surface (h can be considered as the characteristic length of the system from a tablet handling perspective) and D is the pan diameter. Reference: 1.N.K.Jain, pharmaceutical product development. New Delhi.OBS publishers,2006.93.print. N.balaji

hi pavan, various coating machines available in the market are gansons,neocota. Neomachine mfc. Co. Pvt. Ltd., offers neocota, an automatic coating system for tablets and pellets. Neocota is a completely updated automatic coating system having a batch capacity of 500 g to 1 kg. This model efficiently carries out the following operations: aqueous film coating of tablets/pellets; non-aqueous organic solvent-based film coating of tablets/pellets; and enteric film coating of tablets/pellets. The basic unit of the system is: coating pan has perforations along its cylindrical portion. It is driven by a variable speed drive with a flameproof motor. Supply of hot air and exhaust of drying air are arranged to facilitate the coating system through stainless steel plenums positioned on both sides of the perforated coating pan. The pan is enclosed in a cylindrical airtight housing provided with a suitable door and front glass window. This housing of pan with drive is a stainless steel cabinet accommodating the gearbox, ac variable drive, power panel, hot air unit, exhaust unit and an air fitter. Liquid spray system is complete with stainless steel liquid storage vessel, variable flow-rate liquid dosing pump, automatic spray gun, and inter-connecting flexible hoses. Microprocessor-based control panel is complete with printer and is mounted on the cabinet for automatic control of all the coating parameters and data logging. Reference: http://suppliers.jimtrade.com/126/125601/28519.htm N.balaji

hi To reduce hygroscopic core material reformulate core with less hygroscopic material. Reference: 1.N.K.Jain, pharmaceutical product development. New Delhi.OBS publishers,2006.93.print. N.Balaji