Pharmaceutical Manufacturing Handbook: Production and

276 SEMISOLID DOSAGES: OINTMENTS, CREAMS, AND GELS
12% carbohydrates, and 1% free wax alcohols and stearic esters of fatty acids. It is
available as granules or sheets which are white in color and possesses a characteristic
odor. White wax is insoluble in water and melts between 61 and 65 ° C. It has stiffening
and viscosity - enhancing properties and therefore is used in hydrophobic ointments
and oil - in - water creams. Although it is thermally stable, heating to above
150 ° C results in reduction of its acid value. White wax is incompatible with oxidizing
agents. The presence of small quantities of impurities results in hypersensitivity
reactions in rare occasions. Preparations are stored in well - closed, light - resistant
containers in a cool, dry place [13] .
Yellow Wax Yellow wax, also known as yellow beeswax, is obtained from honey
combs. It contains about 70% esters of straight - chain monohydric alcohols, 15%
free acids, 12% carbohydrates, and 1% free wax alcohols and stearic esters of fatty
acids. It is available as noncrystalline pieces which are yellow in color and possesses
a characteristic odor. It is practically insoluble in water and melts at 61 – 65 ° C. It is
used in the preparation of hydrophobic ointments and water - in - oil creams because
of its viscosity - enhancing properties. Concentrations up to 20% are used for producing
ointments and creams. It is incompatible with oxidizing agents. Esterifi cation
occurs while heating to 150 ° C and hence should be avoided during preparation.
Hypersensitivity reactions sometimes occur on topical application of yellow wax –
containing ointments and creams due to the presence of some minor impurities.
These products are preserved in well - closed, light - resistant containers [13] .
Combinations of bases are sometimes used to acquire better stability. Gelling
agents such as carbomers and PEG are also included in some ointment and cream
preparations. Table 3 shows examples of cream bases used in some commercial
cream preparations.
4.2.2.3
Preparation and Packaging
In addition to the base and drug, ointments and creams may also contain other
components such as stabilizers, preservatives, and levigating agents. Usually levigation
and fusion methods are employed for incorporating these components into the
base. Levigation involves simple mixing of base and other components over an ointment
slab using a stainless steel ointment spatula. A fusion process is employed only
when the components are stable at fusion temperatures. Ointments and creams
containing white wax, yellow wax, paraffi n, stearyl alcohol, and high - molecular -
weight PEGs are generally prepared by the fusion process. Selection of levigation
or the fusion method depends on the type base, the quantity of other components,
and their solubility and stability characteristics.
Oleaginous ointments are prepared by both levigation and fusion processes.
Small quantities of powders are incorporated into hydrocarbon bases with the aid
of a levigating agent such as liquid petrolatum, which helps in wetting of powders.
The powder component is mixed with the levigating agent by trituration and is then
incorporated into the base by spatulation. All solid components are milled to fi ner
size and screened before incorporating into the base to avoid gritty sensation of the
fi nal product. Roller mills are used for producing large quantities of ointments in
pharmaceutical industries. Uniform mixing can be obtained by the geometric dilution
procedure, which usually involves stepwise dilution of solids into the ointment