Problems and Solutions in Sugar-coated Tablet Production I
Writer： admin Time：2020-05-13 14:48 Browse：℃
Nowadays, sugar-coated tablets are inadequate in many aspects and sugar coating technique is replaced by film coating technique gradually. However, appearance of sugar-coated tablets, such as smoothness, is still better than that of film coating tablets. Some original patented products are sugar-coated tablets. The goal of these tablets is to overcome the problem of difficult swallowing because some tablets are bitter while the sugar coat can improve their taste and beautify them.
The technique of coating can date back to ancient China. Treatise on Three Categories of Pathogenic Factors (written by Song Yan in 1174 of Song Dynasty) introduces coating of red pellets, which are as large as phoenix tree seeds and coated with cinnabar. In another medical book, edited by Wan Ming of Ming Dynasty, records a pill which is coated with Indigo naturalis and gold foil. Our forefathers coated these medicines according to the functions they should play in practical treatment: to induct the medicines into affected channel, to reduce their toxic actions, to better medicine appearance, to protect medicines, etc. Sometimes, a coat can even be mal-functional.
In traditional sugar coating technique, many auxiliary materials of no medical value, such as talc, sucrose and gelatin, are added to the surface of tablets so that tablets can get 50%-100% additional weight. However, the production is pretty complex and operators can only depend on their experience to control coating quality. Due to a number of uncontrollable factors during sugar coating, many tablets are often broken or blotched, become moldy, disintegrate overtime, contain less and less effective content, have strong hygroscopicity, are difficult to store, etc.. Now some common problems and solutions in sugar-coating procedure are introduced later.
1. Syrup does not stick to the pot and tablets discolor due to friction
Reason: The coating temperature is too low; wax is not removed totally; coating pot is installed in a small angle.
Solutions: clean pot wall or apply syrup to the wall. Talc can help the syrup’s sticking to the wall. Tablets can be coated after the pot is dry. Heat tablets and pot wall uniformly and adjust angle of coating pot properly.
2. Tablets stick to pot wall
Reason: Too much sugar, strong viscosity, uneven stirring or pot temperature is low. Such a phenomenon often happens when coating the isolation layer.
Solution: Temperature of syrup should be controlled within 40-50°C. It is proper to mix 800-900ml syrup with 30kg tablet cores. Its sugar content should be constant in 360g/L. Common concentration of syrup is about 70%. Also, fresh syrup is better. To keep syrup flowing, the pot should be heated and certain temperature kept. If cold syrup is used to coat, the concentration should be lower. In addition, stirring should be timely and evenly and the pot temperature stays in 50°C
3. Drying is slow
Solution: Syrup volume and temperature should be controlled.
4. The coat falls down and tablet cores are not dry
Reason: The tablet cores are not dry; the coats are not dried absolutely and tablet cores are affected with damp; the expanding coefficient of coats and tablet cores are not the same.
Solution: Drying tablet cores, controlling material feeding quantity and speed during coating and controlling drying temperature and degree. If coat falls, the tablet should be decoated and coated again.
5. Tablets are cracked (or sugar coats are full of cracks)
During transition from powder coat to sugar coat, quantity of talc is not proper; the temperature is high leading to high drying speed and raw sugar precipitation; acidic medicine reacts with talc and generates carbon dioxide. Dosage of talc and sugar syrup should be controlled. For example, during transition from powder coat to sugar coat, talc should be used less and less; if medicine is acidic, a separation layer is needed; the temperature of drying should also be controlled. On the other hand, unqualified hardness of tablet cores will lead to cracks. During coating, moisture will spread into tablet cores and cracks occur when the tension of cores are stronger than that of coats. Besides, talc of bad quality contains carbonate, which can react with acidic extract and generate carbon dioxide, leading to cracks. In this case, the hardness of tablet cores should be appropriate to prevent moisture from spreading inwards effectively. Syrup and talc dosageand pot temperature should all be controlled well to form thin film for quick drying. Good quality talc should be used. The end products should be packed separately to avoid moisture.
Solution: controlling syrup and talc dosage, drying temperature and drying degree, using talc containing no carbonate and controlling storing temperature.
6. Tablets are of spot and nonuniform color
Small dosage and multiple layers is the key of coating. Sugar-coated tablets of dark color will generate spot easily, such as green CHloramphenicol Tablets. However, spots of tablets of light color, such as yellow berberine tablets, are less and lighter. Therefore, the product color is better to be light. Colored syrup can be added in small volume and for many times.
Tablet cores should be smooth otherwise they cannot be coated uniformly and spots will occur. The last layer of coat cannot be too wet or too dry. Being too wet or too dry will challenge polishing. The main reasons of spots are uneven powder coat, thin sugar coat, quick sugar coat drying, thin syrup and wrong time to add colorant, etc.
1) Tablet core quality
High moisture of tablet cores will cause colorant migration during drying; uneven surface or break will lead to non-uniform coloring.
2) Technique
Tablet temperature and drying is not controlled well, leading to non-uniform drying; colorant is not stirred uniformly during production.
The temperature during coat cannot be too high. In high temperature, moisture will be evaporated quickly, and crystal separated will rough tablet surface so that spots occur. Hot syrup cannot be used otherwise end products cannot be polished. Heating is not needed, neither. Lingering warmth of tablet cores or pot can evaporate moisture and tablet surface can be smooth.
During colored sugar coating, the dosage of syrup is not coordinate with drying speed (i.e. drying time and temperature). The speed is pretty high. The syrup dries before it coats tablets uniformly.
Before coating, tablet core surfaces are not even so that colorant precipitates and generates spots. This condition is the commonest and is generally caused by too much talc or too quick drying. The color of coat should transit to the dark gradually but not suddenly.
Solution: To smooth tablet surface, syrup of light color can be applied. Pot temperature and drying time should be both controlled and syrup should be totally stirred during production.
3) Colorant
It is suggested to use stable and insoluble colorant. If soluble colorant is used, desalinate first, although this situation is rare. The time to adding colorant is also important. If they are soluble, colorants should be added in the last 3-5 layer coating. However, if they are insoluble, such as iron oxide, colorants should be added into talc and syrup separately in the last several layer coating. Highly transparent iron oxide can be applied for coating. Colorant should be mixed with syrup completely. It should fully dissolve in heating water, and then be heated, added into and mixed with syrup. During coloring, the temperature cannot be too high but keeps lower than 30°C.
