An almost white or pale yellow colored, waxy solid or flakes which
when warmed become plastic before melting. Anionic emulsifying
wax has a faint characteristic odor and a bland taste.
Anionic emulsifying wax is prepared by melting cetostearyl alcohol
and heating to about 95℃. Sodium lauryl sulfate, or some other
suitable anionic surfactant, and purified water are then added. The
mixture is heated to 115℃ and, while this temperature is
maintained, the mixture is stirred vigorously until any frothing
ceases. The wax is then rapidly cooled.
Pharmaceutical Applications
Anionic emulsifying wax is used in cosmetics and topical
pharmaceutical formulations primarily as an emulsifying agent.
The wax is added to fatty or paraffin bases to facilitate the
production of oil-in-water emulsions that are nongreasy. In
concentrations of about 2%, emulsions are pourable; stiffer
emulsions, e.g. aqueous cream BP, may contain up to 10% of
anionic emulsifying wax.
Creams should be adequately preserved and can usually be
sterilized by autoclaving. A better-quality emulsion is produced by
incorporating some alkali into the aqueous phase, although care
should be taken not to use an excess.
Anionic emulsifying wax (3–30%) may also be mixed with soft
and liquid paraffins to prepare anhydrous ointment bases such as
emulsifying ointment BP. A preparation of 80% anionic emulsifying
wax in white soft paraffin has been used as a soap substitute in the
treatment of eczema.
In addition, anionic emulsifying wax (10%) has been added to
theobroma oil (cocoa butter) to produce a suppository base with a
melting point of 34℃.
Anionic emulsifying wax is used primarily in topical pharmaceutical
formulations and is generally regarded as a nontoxic and
nonirritant material. However, sodium lauryl sulfate, a constituent
of anionic emulsifying wax, is known to be irritant to the skin at
high concentrations; sodium cetyl sulfate is claimed to be less
irritating.
Emulsifying ointment BP, which contains anionic emulsifying
wax, has been found to have major sunscreen activity in clinically
normal skin and should therefore not be used before phototherapy
procedures.
Solid anionic emulsifying wax is chemically stable and should be
stored in a well-closed container in a cool, dry place.
Incompatibilities of anionic emulsifying wax are essentially those of
sodium alkyl sulfates and include cationic compounds ( quaternary
ammonium compounds, acriflavine, ephedrine hydrochloride,
antihistamines, and other nitrogenous compounds), salts of
polyvalent metals (aluminum, zinc, tin, and lead), and thioglycolates.
Anionic emulsifying wax is compatible with most acids above
pH 2.5. It is also compatible with alkalis and hard water.
Iron vessels should not be used when heating anionic emulsifying
wax; stainless steel containers are satisfactory.
Included in the FDA Inactive Ingredients Database (rectal emulsions
and aerosol foams; topical aerosols, emulsions, creams, lotions, and
ointments). Included in nonparenteral medicines licensed in the UK.
Included in the Canadian List of Acceptable Non-medicinal
Ingredients.
