A film coating is a thin polymer-based coat applied to a solid dosage form such as a tablet. The thickness of such a coating is usually between 20-100 ┬Ám. Under close inspection the film structure can be seen to be relatively non- homogenous and quite distinct in appearance, from a film forming, from casting a polymer solution on a flat surface.

Types of film coating tablet :

1. Immediate release (non functional) film coating:
They do not affect the biopharmaceutical properties of the tablet. They are readily soluble in water.

Read More :

2. Modified release (functional) film coating:
They allow the drug to be delivered in a specific manner; i.e. they affect drug release behavior. Modified release film coatings are sub classified into :

a. Delayed release coating (enteric coating)
Only soluble in water at pH ≥ 5-6. Intended to protect the drug from gastric acidic pH (for acid labile drugs). Used for colonic drug delivery systems.

b. Extended release coating.
Mostly water insoluble. It designed to ensure consistent drug release manner over a long period of time (6-12 hr) andthus decreasing dosing regimen and improving patient compliance.

Coating Process
Film-coating of tablets is a multivariate process, with many different factors, such as coating equipment, coating liquid, and process parameters which affect the pharmaceutical quality of the final product.

Coating equipment
It is possible to use the conventional "coating pan''. Special equipment may be also used "fluid bed coating equipment".

Before few years different types of coating pans are used for coating like conventional coating pans, manesty accelacota, driam ( driacoater ), butterfly coater etc. Now a days the side-vented, perforated pan-coater is the most commonly used coating device of tablets. In equipment spray nozzle, number of spray nozzle, pan size, etc may also affect the quality of final product. Its air flow system through a perforated pan ensures rapid and continuous drying conditions. The low evaporation capacity of water requires high drying efficiency of aqueous film-coating equipment.

Coating liquid
Coating liquid may affect the final quality of the tablets. Different film former have different chemical nature and different charesteristic. Viscosity may affect the spreading of coating liquid across surface of substrate. Surface tension may affect in wetting of surface. % Solid content generally affect the tablet surface and coating efficiency.

Read More :