Why Coat Tablets?
From that earlier times, the coating is frequently used in dosage forms that are already completely prepared. That means an extensive range of oral solid dosage forms is coated.
Read more - Solid oral dosage Forms (Tablet or Capsules)
There are many reasons that include;
1) To improve the stability of the drugs. The coating protects the drug from the environment like light, air, moisture, etc.
2) There are many uncoated drugs that are very bitter in taste. So, after coating the unpleasant taste and odor can be masked.
3) After coating tablet becomes easier for the patients to swallow it.
4) The coating improves the product identity for both that is for workers as well as for patients.
5) In high-speed packaging lines, the coating makes handling easy. The coating also minimizes the cross-contamination that occurs due to the elimination of dust.
6) Coating also improves the product's appearance, which is important to identify.
7) Especially in the case of active ingredients, coating minimizes the risk of interaction between incompatible compounds or ingredients.
8) The coating improves the product strength because coated drugs are more resistant to abrasion or friction.
9) Coating also modifies the release of the drug if there is a need for repeat action, especially in the case of the delayed-release drug as well as the sustained-release drug.
Read more - How do you prepare a tablet dosage form?
Evaluation of the Coating Process
In earlier times a wide range of coating materials has been used in the coating of tablets. Earlier the coated products were prepared by individuals who worked in the pharmacy without any extra preparation, which is now been prepared by different pharmaceutical industries.
Earlier experiments to apply coating on the tablets shows variable results. These tablets or pills are held with a pair of forceps or mounted on a needle and dipped or pour into the coating solution.
This procedure was repeated again and again to confirm that the tablet was coated completely. After that, the tablet was held at the end of the suction tube, dipped, and then the same process was repeated for the other side of the tablets. But this process failed to produce uniform-coated tablets.
At the start, pharmaceutical pan-coating techniques were used in the candy industry. The candy coating technique generally used coating pans which are made of copper because drying was achieved by applying external heat directly to the coating pan.
Nowadays, the coating pans that are used in pharmaceutical coating techniques are made from Stainless Steel, where the drying of the coated product is done by applying heated air, and moisture, and dust is removed from the pan through the air-extraction system.
The traditional pharmaceutical pan-coating technique is essentially used for sugar coating. Nevertheless, there have been important advances made in the process of coating techniques. Mainly evaluation of the different coating pan designs.
Although in early 1950, the sugar coating technique was dominated as a pharmaceutical coating. Thought, a new form of a technique called film coating technique was also developed.
By identifying the limitations of the sugar coating process, the establishment of the film coating technique shows significant improvement by applying coating formulations that contain polymers that dissolve in highly volatile organic solvents. The result of this technique shows that the coating which took many days to complete could now be completed in a few hours.
Although, the use of organic solvents created many problems that are associated with the poor drying capabilities of the types of equipment that are available at that time. The disadvantage of this perspective was that these organic solvents were highly flammable, toxic in nature, required highly skilled persons for handling, and also showed environmental problems as well.
The advances in the equipment design, and also the introduction of the fluidized bed coating technique show the gradual development of the coating process where the efficiency of drying has been maximized. As film coating becomes a dominant process in pharmaceutical oral solid dosage forms, these improvements in the design of types of equipment have also benefitted the sugar coating technique, which created a fully automated process and also can be prepared in a batch in less than one day as well.
Read more - Common tablet defects appear in the manufacturing of tablets
Tablet Properties
The tablets that are to be coated must have proper physical characteristics. In the process of coating, the tablets roll in a coating pan in the air stream, and the mixture of coating is applied to it.
To bear the friction between other tablets and the wall of the coating pan, the tablet must be resistant to wearing off or cracking and chipping.
The tablet surface that is easily broken or fragile becomes soft in the presence of heat and becomes rough in the starting phase of the coating process and is unacceptable for film coating.
The film coating adheres or sticks to all the surfaces of the tablets so that any surface defect of the tablet is coated and not excluded.
The quality of film coating which is applied on the compressed tablets mainly depends upon the quality of starting tablet than on the time at which sugar coatings are applied. The sugar coating dries very slowly due to the high solid content and fills many minor surface defects of the tablets that occurred early phase of the coating process.
The ideal shape of the tablet for coating is a sphere or round shape that allows the tablet to move freely in the coating pan, with the least tablet-to-tablet friction or contact. The worst shape of the tablet is a square shape or flat-faced tablet in which the coating material collected between the surface of the tablet and the tablet got to stick together. Due to this reason, the coated tablets have rounded or sphere surfaces. Because if the tablet has a convex surface, the lesser the difficulties will be met with tablet lump or mass.
As a formulation compressed tablet contains many ingredients except active drugs to provide an easily compressible and rapidly dissolving dosage form. The surface properties of the tablets totally depend upon the chemical nature of the ingredients that are used in the formulation.
For the coating material that sticks to the tablet, the composition of the coating must be wet on the surface of the tablet. The surface of the hydrophobic tablet is very difficult to coat with aqueous-based coatings because these tablets do not wet the surface.
With the addition of appropriate surfactants, the composition of the coating decreases the surface tension of the coating composition and coating composition and also improves the coating adhesion or sticking.
I hope you like my article What is Coating in Pharmaceuticals? I give up the information about the coating of pharmaceutical dosage forms. If you have any queries or questions related to the article then feel free to ask in the comment section.
Read more - Physical evaluation of a tablet after post-compression
Read more - Pre-compression evaluation of tablets
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