Sugar coating process consists of several stages which ranged from couple hours to several days. A successful product is highly dependent on operator skill. The operator determines the amount of solution to be added, the manner and rate of pouring, when to deliver the air dryer, and how long or how quickly the tablets were rotated in the pan.
The core tablet better convex on the surface, with rounded edges and thin to facilitate the coating with sugar. Because the sugar coating tends to a long and strong shaking, then the core tablet should fairly resistant, not easily broken, chipped, or eroded. For that, the first tablet core must have a high friability values.
It involves successive application of sucrose based coating formulations to tablet cores, in suitable coating equipment. Water evaporates from the syrup leaving a thick sugar layer around each tablet. Sugar coats are often shiny and highly colored.
Typically, tablets are sugar coated by panning technique, using traditional rotating sugar coating pan with a supply of drying air (thermostatically controlled).
The pan is automatically rotated, allowing tablets to tumble over each other while making contact with the coating solutions which are gently poured or sprayed, portion wise onto the tablets with warm air blown to hasten drying. Each coat is applied only after the previous coat is dried.
Steps for sugar-coating process:
1. Sealing (Waterproofing)
To improve drug stability by protecting it from the moisture gained from the following steps. May be used to obtain modified release characteristics.
This involved the application of one or more coats of a waterproofing substance in the form of alcoholic spray, such as pharmaceutical Shellac (traditionally) or synthetic polymers, such as CAP.(N.B.Unless a modified release feature needs to be introduced, the amount of the sealing coat applied should be carefully calculated so that there is no negative effect on the drug release characteristics in case of immediate release product.)
The purpose of this sealing step is :
a. Sugar coatings are aqueous formulations which allow water to penetrate directly into the tablet core and thus potentially affecting product stability and possibly causing premature tablet disintegration.
b. Application of many coats of partially or completely water insoluble polymers in this step, enables sugar coated product to exhibit modified release pattern (extended release or delayed "enteric" release characteristics).
Large quantities of sugar coatings are usually applied to the tablet core (typically increasing the tablet weight by 50-100%), in order to round off the tablet edge. Much of this material build up occurs during this stage and is achieved by adding a bulking agent such as Calcium carbonate, to the sucrose solution.
Antiadherents, e.g. Talc may be added after partial drying to prevent sticking of the tablets together.
N.B. These procedures may be repeated till the desired shape and size areobtained.
The subcoating stage results in tablets with rough surfaces. To facilitate the color application (which requires a smooth surface),subcoated tablets are smoothed out by a thick sucrose syrup coating.
Color coatings usually consist of thin sucrose syrup containing the requisite coloring materials. (water soluble dyes or water insoluble pigments may be used)
N.B. This step must be done into a clean pan deprived of any residues from the previous operations.
After the coloring step, the tablet surfaces tend to be smooth but somewhat dull in appearance. To achieve glossy finish, final stage involving application of waxes (beeswax or carnuba wax) is employed.
Different tablets could be identified by manufacturer ‘logo, product name, dosage strength or other appropriate code. For sugar coated tablets, such identification could be only achieved by printing process using special edible inks.