REVIEW: TABLET COATING PROCESS

ABOUT AUTHOR
Abhijeet Welankiwar

Govt. College of pharmacy, kathora naka,
Amravati (Maharashtra) 444604
abhi123welankiwar@gmail.com

ABSTRACT:
Tablet coating is the key step involved in the manufacturing of tablets having controlled release, delayed release profiles. The tablet coating have number of advantages like masking odor, taste, color of the drug, providing physical and chemical protection to drug, Protecting drug from the gastric environment. 3 primary components of tablet coating are tablet properties, coating process and coating composition. Tablets are usually coated in horizontal rotating pan with coating solution is either directly poured or sprayed on to them. The amount of coating on the surface of a tablet is critical to the effectiveness of the oral dosage form. Recent trends in tablet coating focuses on overcoming disadvantage of solvent based coating. This article concerns with the coating process, equipments involved, coated tablets evaluation and specialized coating techniques.

REFERENCE ID: PHARMATUTOR-ART-1732

INTRODUCTION:
Tablet is a pharmaceutical dosage form. It comprises a mixture of active substances and excipients, usually in powder form, compressed or compacted into a solid. Tablets Dosage form is one of a most preferred dosage form all over the world. Almost all drug molecules can be formulated in a tablet and process of manufacturing of tablets is very simple, and is very flexible. One can administered 0.01 mg of a drug dose to 1 gm of a drug dose by oral route of administration, by formulating as a tablet. Coating is a process by which an essentially dry, outer layer of coating material is applied to the surface of a dosage form in order to confer specific benefits that broadly ranges from facilitating product identification to modifying drug release from the dosage form.

Basic principles involved in tablet coating are: -
Tablet coating is the application of coating composition to moving bed of tablets with concurrent use of heated air to facilitate evaporation of solvent.
1. Solution in which influences the release pattern as little as possible and does not markedly change the appearance.
2. Modified release with specific requirement and release mechanism adapted to body function in the digestive tract.
3. Color coating which provides insulation.
4. To incorporate another drug or formula adjuvant in the coating to avoid chemical incompatibilities or to provide sequential drug release.
5. To improve the pharmaceutical elegance by use of special colors and contrasting printing.

There are 3 primary components of tablet coating: -
1. Tablet properties.
2. Coating process.
        Coating equipments.
        Parameters of the coating process.
        Facility and ancillary equipments.
        Automation in coating process.
3. Coating composition.

Tablet properties: -
1) Tablet must be resistant to abrasion and chips.
2) The ideal shape of the tablet for coating is sphere.
3) The hardness of the tablet should not be less than 5 kg/cm2
4) The tablet must have good friability.
5) Tablets must have good flow.

Coating process: - The basic principle of tablet coating is simple. Tablet coating is an application of coating composition to a moving bed of tablets with the concurrent use of heated air to facilitate evaporation of the solvent. The distribution of coating is accomplished by the movement of the tablets either perpendicular (coating pan) or vertical (air suspension).

A. Coating equipments: - For the coating process use of one of the 3 types of following equipments. 1) Conventional coating pan. 2) The perforated coating pan. 3) The fluidized bed coater.

1) Conventional coating pan: - Improvements in conventional pan are pellegrini system which has a baffled pan and diffuser The immersion sword system and the immersion tube system all of them have enhanced drying efficiency compared to older models. The newer models are completely enclosed.

2) The perforated coating pan: - The e.g. in this class are Accela-cota, Hi-Coater system Diracoater and the Glatt coater.

3) The fluidized bed coater: - The fluidized bed coaters have enhanced drying efficiency fluidization of tablet mass is achieved by columnar chamber by the upward movement of the drying air. The movement of the tablets is upward through the center of the camber. Then they fall toward the chamber wall and move downward to re-enter into air stream at the bottom of the chamber. It has a basically two spray application systems they are (1) high pressure airless (2) low pressure air atomized.

Coating techniques: - Generally three methods are used for tablet coating A) Sugar coating. B) Film coating. C) Enteric coating.

A) Sugar coating: -
I. Sealing/Water proofing: provides a moisture barrier and harden the tablet surface.
II. Sub coating causes a rapid buildup to round off the tablet edges.
III. Grossing/Smoothing: smoothes out the sub coated surface and increases the tablet size to Predetermine dimension.
IV. Coloring gives the tablet its color and finished size.
V. Polishing produces the characteristics gloss.

B) Film coating: - Film coating and the sugar coating share same equipment and the process parameters. There are basically 2 methods of film coating they are
I. Pan pour methods: Tablets coated by pan pour method subjected to alternate solution application, mixing and drying steps are similar to pan pour sugar coating. This method is relatively slow and relies heavily on the skill of operator.
II. Pan-spray methods: The introduction of spraying equipment was the next evolution in improving the film coating process allows for automated control of liquid application. Broad flat spray patterns are usually chosen by appropriate nozzle systems.

Development of film coating formulations:
If the following questions are answered concomitantly then one can go for film coating:
i) Is it necessary to mask objectionable taste, color and odor?
ii) Is it necessary to control drug release?
iii) What tablets size, shape, or color constrains must be placed on the developmental work?

Materials used in film coating:

Sr.no

Material

Type

Example

1

Film formers

Enteric, Non enteric

HPMC, Ethyl cellulose, Sod. CMC, Polyethylene Glycol, Cellulose acetate phthalate, HPMCP

2

Solvent

-------

IPA and Methylene chloride.

3

Plasticizers

Internal plasticizing

External plasticizing

Castor oil, Propylene glycol, Glycerin, surfectants, polysorbates.

4

Colorants

Inorganic colorants

Natural colorants.

FD and C colors, D and C colors, iron oxides, Carmel, turmeric.

5

Opacifiers

----------

Titanium dioxide, talc, aluminum silicate.

C) Enteric coating: - ideal properties of enteric coating material are:
1) Resistant To gastric fluids.
2) Compatibility with most of the coating solutions
3) Non toxicity.
4) Low cost.
5) Ease of application
6) Formation of continuous film.

Polymers used in enteric coating are: -
Cellulose acetate phthalate.
Acrylate polymers.
Hydroxypropyl methylcellulose Phthalate.
Polyvinyl acetate phthalate.

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