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Jun 22, 2018

 COLOURANTS/OPACIFIERS

• Identification of the product by the manufacturer and therefore act as an aid (not a replacement)
for existing GMP procedures. Colourants also aid in the identification of individual products by
patients, particularly those taking multiple medication.
• They reinforce brand imaging by a manufacturer and thereby decrease the risk of counterfeiting.
• Colourants for film-coated tablets have to a greater or lesser extent opacifying properties which
are useful when it is desired to optimize the ability of the coating to protect the active ingredient
against the action of light.

1. Classification

Organic dyes and their lakes
This group would include such materials as Sunset Yellow, Patent Blue V, Quinoline Yellow, etc. As
water solubles their use is extremely restricted regarding the colouring of any form of coated tablet.
However, their water-insoluble complexes with hydrated alumina, known as lakes, are in widespread
use as colours for coated tablets. The reason for this will be considered in the appropriate section below.
In the laking process a substratum of hydrated alumina is produced by reacting aluminium chloride with
sodium carbonate. The appropriate dye in aqueous solution is then adsorbed onto the prepared alumina
hydrate. Finally additional aluminium chloride is added to ensure complete formation of the aluminium
salt of the dye. Filtration and washing of the product complete the process.
Inorganic colours
Stability towards light is an important characteristic displayed by these materials, some of which have a
useful opacifying capacity, e.g. titanium dioxide. Another great advantage of inorganic colours is their
wide regulatory acceptance, making them most useful for multinational companies wishing to
standardize international formulae. One drawback to their use is that the range of colours that can be
achieved is rather limited.
Natural colours
This is a chemically and physically diverse group of materials. The description ‘natural’ is of necessity
loose, as some of these colours are the products of chemical synthesis rather than extraction from a
natural source, e.g. (β-carotene of commerce is regularly synthetic in origin. The term frequently applies
to such materials is ‘nature identical’, which in many ways is more descriptive. Some would even make
the case that any product which is not a constituent of the normal diet should not be called ‘natural’.
This viewpoint would remove colours such as cochineal and annatto from consideration. As a
generalization, natural colours are not as stable to light as the other groups of colours; their tinctorial
powers are not high and they tend to be more expensive than other forms of colour. They do, however,
possess a regulatory advantage in that they have a wide acceptability. Even with these advantages their
penetration into the pharmaceutical area has not been great.

This group of materials are commonly used as ingredients in film-coating formulae. They obviously
contribute to the aesthetic appeal of the product, but they also enhance the product in other ways:
Examples of colours:
Organic dyes and their lakes
Inorganic colours
Natural colours








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