The active pharmaceutical ingredients (API) are not used as such but are suitably formulated into dosage forms or drug delivery systems in an attempt to ensure safe, efficient, reproducible and convenient manner of drug delivery. The dosage forms are not API alone but contain many other additives. These additives are known as excipients.

The pharmaceutical excipients are defined as substances (other than API) which have been appropriately evaluated for safety and included in a dosage form to: add in processing of dosage form during its manufacture; protect, support, or enhance stability, bioavailability or patients acceptability; assist in product identification; or enhance any other attribute of overall safety and effectiveness of the API during storage or use. While the API is the primary constituent of the pharmaceutical product, the pharmaceutical excipients contribute to the physical form, texture, stability, taste and overall appearance.

The patients’ medication adherence is most vital in therapy to get the optimum outcome. The medication adherence often closely related to the odour, taste and colour of the product. The proper combination of the flavour, fragrance and colour in a dosage form contribute to the acceptance of the pharmaceutical products. The flavouring, sweetening and colouring agents are grouped together as organoleptic excipients.

The flavouring agents are included to improve the taste of the product either by providing a more pleasant taste or by masking the unpleasant taste. In general flavouring of liquid products requires better expertise than solid pharmaceutical dosage forms. Medications in liquid forms directly come in contact with taste receptor cells in the mouth and produce positive or negative taste sensation.

The selection of the flavouring agents depends on many factors primarily on the taste of API and the age of the intended patient. There are four basic types of taste: salt, sour, bitter and sweet. Certain flavouring agents are more effective than others in masking or disguising the particular taste. Though the individuals’ choices vary, there are certain general concepts: cocoa flavours are preferred for masking taste of bitter medicinal agents; fruits or citrous flavour to combat sour or acid tasting API; and cinnamon, orange, and raspberry flavour for salty medicinal ingredients. The age of the patient is too crucial in selection of the flavour.  Children like sweet candy like preparations with fruit flavour but adults may prefer less sweet preparation with a tart.  The elderly persons may have liking for wine flavour.

The oral solid dosage forms like capsules and coated tablets do not need flavouring agents in their formulation. On the other hand, the chewable or effervescent tablets do need flavours and also sweetening agents to improve acceptance.  As the flavouring agents are often thermolabile, the time of addition of flavour in tablet formulation is critical. They cannot be added to an operation involving heat (drying of granules). They may be mixed with the granules prior to compression as alcoholic solutions.

The flavouring agent in liquid dosage forms is added to the solvent or vehicle component of the formulation in which it is most soluble or miscible. The water soluble flavouring agents are added to the aqueous component of the formulation and poorly soluble are added to the alcoholic or other non-aqueous solvent component of the formulation. In multi-component systems, the appropriate solvent level of the flavouring agent is essential to keep them in solution.

Sucrose, a low molecular weight carbohydrate, has been traditionally used as sweetening agent because of several advantages associated with it: very soluble in water, stable over a pH range of 4 to 8, increases viscosity which impart a product a pleasant  texture in the mouth. However, it is also associated with two issues: use in diabetic patients and its cariogenic properties. Polyhydric alcohols: sorbitol, mannitol, and to some extent glycerine have sweetening properties and can be used in preparations for diabetic patients. In addition, there are many artificial sweeteners. They are sweeter than the sucrose and are suitable for patients who need to restrict their sugar intake. But there are several safety issued raised on some of them especially on: saccharin, aspartame and cyclamate.

 Saccharin does not undergo metabolism and its potential for causing cancer is determining factor for its use. Aspartame undergoes metabolism producing phenylalanine and the phenylalanine metabolism is a problem in persons with phenylketonuria. The increased serum level of phenylalanine amino acid can cause mental retardation and affect the foetus of a pregnant woman.  Cyclamate is metabolised and its by products are excreted in kidneys. Its safety issues concern with possible carcinogenicity, possible causation of genetic damage and testicular atrophy. However, in addition of safety concern, they have the disadvantages of being imparting a bitter or metallic after taste.

The colouring agents are included in the dosage forms not only to improve the attractiveness of the product, but also to enable easy product identification, particularly in poisonous materials. The presence of strongly coloured inert degradation product can be masked by the use of suitable colours. The natural colouring agents like carotenoids, chlorophyll, anthocyanins, riboflavines, caramel and extracts of beetroot have better acceptability. But they have the usual problems like variations in availability and chemical composition leading to formulation difficulties. On the other hand, synthetic or coal tar dyes provide bright colours with greater stability. Many of these synthetic dyes are found to be hazardous to health because of their own chemical nature or the impurities present. Because of their toxicity or carcinogenicity tendency, they are regulated and only approved colouring agents can be used in pharmaceutical products.

The Drugs and Cosmetics Act and the Rules of India specified what colouring agents can be included in dosage forms. The FDA of USA has classified the colouring agents according to their use: Colours for use in Foods, Drugs and Cosmetics; Colours - some of which for use in drugs, some of which in cosmetics and some are for medical devices; colours for use in externally used products (not in lips or other mucous surface of the body).  The colour acceptable in one country may not be acceptable in another country. It is necessary that the current regulation relating to use of colouring agents in medicines be referred for formulating products meant for export. The nomenclature of the colours too causes confusion. The selection of colours and maintaining a reproducible colour of the product from batch to batch is a highly skilled job. The slight change in intensity of the colour raises doubt about the product in consumer’s mind.

While formulating, it is necessary to consider colour, odour, texture and taste together and not in isolation. The colour of pharmaceutical products must have a psychogenic balance with the taste and the colour must enhance the taste.

Dosage form manufacturers must perform at least one test to verify the excipients’ identity and to check conformity with specification for purity, strength and quality in order to ensure manufacturing of consistent and reproducible products. Though suppliers’ test may be acceptable, at least one test is essential for validation.  If the excipient manufacturer does not provide the result for specification test, it should be indicated on the certificate of analysis. The dosage form manufacturer needs to perform these tests.  They need to comply with country’s regulations in identifying these excipients.