Coloring Agents

Synonyms: Beta-carotene; indigo carmine; iron oxides; sunset yellow FCF; tartrazine; titanium dioxide.

Description: The physical appearances of coloring agents vary widely.

Chemical Name: 

Colorant; opacifier.

• Coloring agents are used mainly to impart a distinctive appearance to a pharmaceutical dosage form.

• The main categories of dosage form that are colored are: .

  • Tablets: either the core itself or the coating. .
  • Hard or soft gelatin capsules: the capsule shell or coated beads. .
  • Oral liquids. .
  • Topical creams and ointments.

• Color is a useful tool to help identify a product in its manufacturing and distribution stages.

• Patients, especially those using multiple products, often rely on color to be able to recognize the prescribed medication.

• The use of different colors for different strengths of the same drug can also help eliminate errors.

• Many drug products look similar; hence color in combination with shape and/or an embossed or printed logo can help with identification. Also, this combination can assist in the prevention of counterfeiting.

• Unattractive medication can be made more acceptable to the patient by the use of color, and color can also be used to make a preparation more uniform when an ingredient in the formulation has itself a variable appearance from batch to batch.

• Some of the insoluble colors or pigments have the additional benefit when used in tablet coatings or gelatin shells of providing useful opacity, which can contribute to the stability of light-sensitive active materials in the tablet or capsule formulation.

• Pigments such as the iron oxides, titanium dioxide, and some of the aluminum lakes are especially useful for this purpose. Of the many classifications possible for pharmaceutical coloring agents, one of the most useful is to simply divide the colors into those that are soluble in water (dyes) and those that are insoluble in water (pigments).

• Colors for clear liquid preparations are limited to the dyes.

• For surface coloration, which includes coated tablets, the choice of color is usually restricted to insoluble pigments.

• The reasons for this include their lack of color migration, greater opacity, and enhanced color stability over water-soluble colors.

• Lakes are largely water-insoluble forms of the common synthetic water-soluble dyes.

• They are prepared by adsorbing a sodium or potassium salt of a dye onto a very fine substrate of hydrated alumina, followed by treatment with a further soluble aluminum salt. The lake is then purified and dried.

• Lakes are frequently used in coloring tablet coatings since, for this purpose, they have the general advantages of pigments over water-soluble colors.

for incompatibilities of specific selected coloring agents; see also Woznicki and Schoneker, and Walford.

Coloring agents are used in a variety of oral and topical pharmaceutical formulations, in addition to their extensive use in foodstuffs and cosmetic products. Toxicology studies are routinely conducted on an ongoing basis by organizations such as the World Health Organization (WHO), the US Food and Drug Administration (FDA), and the European Commission (EC). The outcome of this continuous review is that the various regulatory bodies around the world have developed lists of permitted colors that are generally regarded as being free from serious adverse toxicological effects.

Pharmaceutical coloring agents form a diverse group of materials and manufacturers’ data sheets should be consulted for safety and handling data for specific colors. In general, inorganic pigments and lakes are of low hazard and standard chemical handling precautions should be observed depending upon the circumstances and quantity of material handled. Special care should be taken to prevent excessive dust generation and inhalation of dust.

Beta-carotene; indigo carmine; iron oxides; sunset yellow FCF; tartrazine; titanium dioxide