Parenteral preparations active substance solubility

Water for injection is the preferred vehicle for the preparation of parenteral solutions (injections and infusions). When the active substance is poorly or not soluble in water, co-solvents or non-aqueous vehicles can be employed, or dosage forms such as hposomes or microspheres can be used. 

Emulsions can often been found as dermatological preparations, and sometimes as injections and oral preparations. They make combinations of immiscible liquids possible, typically of fatty/UpophUic components and water. The fat/lipophilic ingredients can act as an active substance, for example, in creams to keep the skin hydrated. They can also serve as a solvent for other substances such as diazepam in Diazemuls injection or for fat soluble vitamins in parenteral nutrition (see Sect. 13.9.2). 

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