FILM COATING TECHNOLOGY: AN OVER VIEW

About Authors:
G. Sowjanya*, P. Ramaa Bharathi, Dr.A.M.S.Sudhakar Babu
A.M.Reddy memorial college of pharmacy,
Narasarao Pet.
Sowjanya.gedagamma@gmail.com

Abstract
Film coating technology is now a days very important in the field of pharmacy particularly in formulation development. In the last 25 years tablet coating has undergone several fundamental changes. Many modifications were advocated to improve the basic process and film coating chosen in place of sugar coating. Film coating is the process whereby a tablet, capsule, or pellet is surrounded by a thin layer of polymeric material. Tablet film coating is performed by two types, one is aqueous film coating (generally water is used as a solvent) and non aqueous film coating (generally organic solvent are used). Film coating formulations usually contain Polymer, Plasticizer, Colourants / Opacifiers, Solvent / Vehicle. Many film coating materials have functional properties which enable the creation of sustained or delayed (enteric) release dosage forms. Coating solution composition may affect the quality of final coated tablets. Optimization of composition of film coating solution is also required. This article discusses tablet coating process, film coating, process parameters, film coating advantages and applications, components of film coating, evaluation of film coated tablets, film defects etc.

REFERENCE ID: PHARMATUTOR-ART-2004

Introduction
All drugs have their own characteristic, like some drugs are bitter in taste or has an unpleasant odor, some are sensitive to light or oxides, some are hygroscopic in nature. Because of this reason tablet coating is the choice of option to solve such problems in conventional dosage form.

In the past sugar coating was mostly borrowed from the confectionary industry. But now a days it is replaced with film coating, because the sugar coating process was a skilled manipulative process and could last for even five days. The operator must be highly skilled for such coating. Hence film coating is preferred over sugar coating.

Coating:
A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. In many cases coatings are applied to improve surface properties of the substrate, such as appearance, adhesion, wetability, corrosion resistance, wear resistance, and scratch resistance.

“ Why Tablet Coating is Required ? ”
A number of reasons can be suggested:
* The core contains a material which has a bitter taste in the mouth or has an unpleasant odour.
* Coating will protect the drug from the surroundings with a view to improve its stability.
* Coating will increase the ease by which a tablet can be ingested by the patient.
* Coating will develop the mechanical integrity, means coated products are more resistant to mishandling (abrasion, attrition etc.)
* The core contains a substance which is incompatible in the presence of light and subject to atmospheric oxidation, i.e. a coating is added to improve stability.
* The core alone is inelegant.
* The active substance is coloured and migrates easily to stain hands and clothes.
* The coated tablets is packed on high-speed packaging machine. Coating reduces friction and increases packaging rate.
* Coating can modify the drug release profile, e.g., enteric coating, osmotic pump, pulsatile delivery.

Classification of coating process:
Coating processes are classified as follows:

Chemical vapor deposition
Here, a fluid precursor undergoes a chemical change at a solid surface, leaving a solid layer.

Chemical deposition is further categorized by the phase of the precursor:
Plating
Chemical solution deposition
Spin coating
Chemical vapor deposition(CVD)
Atomic layer deposition(ALD)

Physical deposition
Physical depositionuses mechanical, electromechanical or thermodynamic means to produce a thin film of solid.

preparation and use of coating solution/dispersions:
Ensure complete and uniform dissolution/dispersion of all coating  ingredients throughout the coating process
Maintain viscosity of coating solution/dispersion throughout the coating process
Keep fluid lines free of any aggregates of solid material throughout the coating process.
Limit the amount of air entrapment/foam creation during coating solution/dispersion preparation and throughout the coating process

Product characteristics of the coating
- Low abrasion, smooth surface
- Good flow behaviour
- Masking of taste and smell
- Good protection against light, air and moisture
- Impervious separating layers in the case of multi-layer composition
- Systematic release of active ingredients
- Retardation, delayed dissolving
- Low hygroscopicity
- Visual attractiveness (pharmaceutical drug safety)

Film coating:
Film coating is the process whereby a tablet, capsule, or pellet is surrounded by a thin layer of polymeric material

Film coating is Application of thin barrier films, protective layers and coloured of functional coatings and it involves

Specific manipulation of product  characteristics.
- Systematic release of active ingredients.
- Gastric juice resistance.
- Taste masking.
- Visual attractiveness

Functional coating tablets.
- Active ingredient can be incorporated in the tablet coating

Uniform and Dense coating
- Low coating mass in comparison with particle centre

Coating Thickness
- Between approx 5 micro meter and 50 micro meter (and more)

Film coating-types:
Tablet film coating is performed by two types, one is aqueous film coating (generally water is used as a solvent) and non aqueous film coating (generally organic solvent are used.) Some problems are associated with the non aqueous film coating like employee safety (it’s dangerous, it smells, and it’s not good to breathe.) atmosphere pollution etc.  But key problem is with the approval of the regulatory authority.  Highquality  aqueous  film  coating  must  be  smooth , uniform  and  adhere satisfactorily to the tablet surface and ensure chemical stability of a drug

Aqueous vs Solvent Film Coating

Solvent based coating solutions / suspensions (e.g. alcohols, methylene chloride)

-  Rapid drying time due to inherent volatility

-  Can be applied to moisture sensitive products

-  Operator safety issues

-  Requires modification to equipment and facility (flame-proofing / intrinsically safe)

-  Environmentally responsible disposal is expensive (solvent recovery)

-  Can impart taste / smell to the product

  Aqueous based processes are now the most common

-  No safety issues (e.g. can allow mobile vessels)

-  Can release to atmosphere

-  Takes longer and may lead to mechanical damage as tablets are tumbled for longer

-  Requires more efficient drying air plant

Advances in drying efficiency has allowed aqueous processes to be developed
even for moisture sensitive products

Table 1: Reasons for film coating

 Reasons for film coating include:

Appearance

To change the color, for branding purposes or other aesthetic reasons

Stability

To protect the active ingredient from moisture, light, and/or the acidic environment of the stomach

Taste/odor  Masking

To provide an easy to swallow tablet without the bitter taste of many actives

Release characteristics

Many film coating materials have functional properties which enable the creation of sustained or delayed (enteric) release dosage forms

Film Coating advantages

  • Minimal weight gain (2-3% as opposed to 60-80 % for sugar coating)
  • Coat is less likely to affect disintegration
  • Single stage process an so generally quicker
  • Easy to automate (less reliance on skilled operator / easier to meet GMP requirements of SOPs, validation etc) Maintains original shape of the core & allows for embossing
  • Expensive equipment & plant requires large space
  • High installation & energy costs

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