Objectionable taste in the formulation may lead to nausea, vomiting and patient non-compliance. An attractive flavor will encourage palatability and easy administration. The four basic taste sensations are salty, bitter, sweet and sour. A combination of flavoring agents is usually selected based on the nature of formulation and age group of the patients to whom it is administered. Table 6.3 provides a list of flavors recommended based on the taste sensation.

Table 6.3 Taste Sensation and the Recommended Flavors

Manufacturing Consideration of Monophasic Liquid Dosage Forms

The following need to be considered in the manufacture of monophasic liquid dosage forms:

1. Raw materials: Raw materials should be tested against specifications such as identity, purity, uniformity and freedom from microbial contamination before the start of manufacturing process. Additional processing such as size reduction, milling or sterilization is required before manufacturing. In preparation of oral liquids, the water used should meet the pharmacopoeial requirements. It should be obtained by distillation or ion exchange treatment.
2. Equipment: The following types of equipment should be used in the manufacture of oral liquid solutions:
   1. Stainless steel mixing tanks and storage tanks equipped with an agitator
   2. Measuring devices for large and small amounts of solids and liquids
   3. A filtration system
   Tanks are usually constructed of stainless steel and are jacketed to allow for heating or cooling of the contents. They are covered and equipped with transparent charging ports and illumination for easy observation of the contents. If the tanks are used for the compounding of bulk liquid, they have a built-in agitation system. The compounded liquid may then be transported to the filling line, either by manually filling into portable transport tanks or by pumping through a liquid delivery unit. All the equipment and pipelines should be easy to disassemble, clean and sanitize. All equipment must be thoroughly cleaned and sanitized before use. The commonly used disinfectants for cleaning of equipments are dilute solutions of hydrogen peroxide, phenol derivatives and paracetic acid. The equipment is sterilized by use of alcohol, boiling water, autoclaving, steam or dry heat.
3. Method of manufacture: Purified water is heated to approximately 50°C–60°C to facilitate the dissolution of the solid solutes, which are added to warm water and stirred to dissolve the drug. Additives should be dissolved separately and then mixed with the bulk mixture. Large volume liquids such as glycerol and sorbitol solution are added and mixed until homogeneous. Coloring agents should be dissolved in a small amount of water and then transferred to the bulk mixture. Flavoring agents should be added at low temperature especially at the end since most of the flavors are volatile. The flavor should be dissolved in a small amount of alcohol, propylene glycol or glycerin and mixed with the bulk mixture. The final volume is made up to the mark with purified water. The mixture is agitated thoroughly until homogeneity is obtained. Finally, the product should be filtered to get a clear solution.