Wax, nonionic emulsifying

• BPCetomacrogol Emulsifying Wax
• USP–NFEmulsifying Wax

cetomacrogol emulsifying wax; emulsifying wax (USP-NF); nonionic emulsifying wax; Polawax

Mixture of cetostearyl alcohol with a polyoxyethylene-based non-ionic surfactant (cetomacrogol 1000 in the BP material; a polyoxyethylene derivative of a sorbitan fatty acid ester in the USP-NF material) · [—]

Polymer, mixture or material of variable composition — no single molecular formula applies.

Surfactant, emulsifier, Semi-solid base, emollient

Typical concentrations: — · Dosage forms: Semi-solid

Used as an emulsifying and stiffening agent to make oil-in-water creams and lotions and water-miscible ointments, particularly when the formulation contains ionic ingredients or a pH that would destabilise soap-based or anionic emulsifiers. For example, Cetomacrogol Emulsifying Ointment BP contains 30% w/w of the wax, and Cetomacrogol Cream BP is made from that ointment. The level used depends on the consistency required.

A white or off-white waxy solid or flakes with a faint odour of cetostearyl alcohol. It melts to a clear liquid and disperses in hot water with stirring to form an emulsion.

Melting range

about 48–56 °C

pH

about 5.5–7 (aqueous dispersion)

Ionic character

non-ionic; tolerant of electrolytes and of a wide pH range

Solubility

soluble in chloroform and ether; partly soluble in ethanol; practically insoluble in water, but dispersible in hot water

Stable. Store in a well-closed container in a cool, dry place. Creams made with it can support microbial growth and need a suitable preservative.

Compatible with most ionic ingredients and many electrolytes. The polyoxyethylene component can bind phenolic and paraben preservatives, reducing their antimicrobial activity, and may be incompatible with phenols such as resorcinol and with tannins. Avoid strong oxidising agents.

Prepared by melting cetostearyl alcohol and mixing it with the non-ionic surfactant (for the BP material, cetomacrogol 1000 in a ratio of about 4 to 1), then cooling and flaking the blend.

Used in topical products and generally regarded as non-toxic and non-irritant. The cetostearyl alcohol component occasionally causes contact sensitisation.

Observe normal precautions for the quantity handled. Eye protection and gloves are recommended. It is combustible.

Included in the FDA Inactive Ingredient Database (topical preparations) and in non-parenteral medicines licensed in Europe.

Anionic emulsifying wax; cetostearyl alcohol; polyoxyl 20 cetostearyl ether (cetomacrogol 1000); polysorbates.

The BP and USP-NF materials are not identical, because they use different non-ionic surfactants, so they should not be assumed to be interchangeable. Nonionic emulsifying wax is the base of choice for creams containing cationic drugs or preservatives, which would be incompatible with anionic emulsifying wax.