Up to 20 percent of water or 5 percent of alcohol can be added to
(2) Summary of water-soluble bases. We can sum up the important aspects
of the water-soluble ointment bases as follows:
(a) Properties. Anhydrous, but will absorb water and dissolve in water;
(b) Examples. Carbowax compounds such as the polyethylene glycol
ointment already mentioned, water-soluble ointment base (a federally stock-listed item
of supply procurement), and bases containing pectin, cellulose, bentonite, and gelatin.
(c) Advantages. Wide range of compatibility; do not become rancid or
support microbial growth; nonirritating (to the same degree as lanolin, petrolatum, etc);
adhere well to skin; easily washed off; low incidence of sensitization.
(d) Disadvantages. Sometimes undergo gradual discoloration with
certain drugs. Unless cetyl alcohol is added, an aqueous solution can be added only to
the extent of 5 percent.
PREPARATION OF OINTMENTS
Ointments are prepared in the pharmacy by either incorporating the active
ingredient(s) into the chosen base or by melting the base and active ingredient(s)
together. The two methods are presented below:
a. Incorporation Method.
(1) Equipment. Most ointments made in the pharmacy are prepared simple
incorporation, in a mortar either with a pestle or on an ointment slab with a spatula. An
ointment slab is a heavy piece of glass with a rough surface on one side to help reduce
the size of solid particles.
(2) Procedure. Triturate solid ingredients in a mortar until they are very fine.
Then, in a mortar or on an ointment slab, make a paste of the powder with an equal
amount of base. This is called levigation. Thoroughly mix the paste with another
volume of base equal to that of the paste. Then continue this routine of mixing equal
amounts of paste and base until the entire base has been added and you have a
uniform preparation with a very small particle size. A mortar and pestle should be used
for incorporating liquids into a base or for preparing larger quantities of an ointment.