Water is the most important liquid to all living organisms. It comprises about 57
percent of your body weight. It is the solvent for or is contained in most of the nutrients
your body requires for growth or maintenance. It is also the primary vehicle for almost
all liquid pharmaceutical preparations. Because of the inherent importance of water in
the practice of medicine, it is essential to acquire some knowledge of the properties of
water and aqueous (water-based) solutions.
a. Properties of Water. All of us are familiar with some properties of water.
We know that generally water is a bland-tasting, colorless liquid. Other specific
properties of water are of importance in medicine.
Its boiling point is 100C (212F).
Its freezing point is 0C (320F).
It is a polar solvent (dissolves ionic compounds).
Generally, it is chemically inert (unreactive) in biological or drug
b. Importance of Properties. The properties above are the specific reasons
that water is so valuable to living systems and to pharmaceutical preparations. The
wide difference between the freezing point (water as ice) and the boiling point (water as
steam or vapor) indicates that water will be a liquid at most of the temperatures
encountered under normal conditions. An example should help emphasize the
importance of these properties. If we wanted to prepare a liquid drug solution for a
patient who could not swallow capsules, we used a liquid vehicle with a freezing point of
25o C (77o F) and a boiling point of 30o C (86o F), we would be giving the patient a
worthless product. As the patient left home, the drug solution would boil if it were a
normal summer day (temperature = 86o F), and when the patient entered his air-
conditioned home, the remaining solution might become a solid which could not be
poured from the bottle. We also want our vehicle to be as unreactive as possible so
that only the drug is exerting a pharmacological effect.